Tesi sul tema "Australian rainfall"

[Abstract]: Australia is one of the driest continents in the world, and over the past decades, severe drought has plagued most of the country. Water security is an important national issue. The ultimate water supply, rainfall, however, is one of the most variable ones in theworld and is complicated by the fact that it is affected by several remote oceanatmospheric teleconnection systems simultaneously, including the El Niño-SouthernOscillation, the Indian Ocean Dipole and Southern Hemisphere oceanic and atmospheric variability. These three systems sometimes conspire to produce a severe impact, whereas sometimes they offset each other to produce a mild influence. The recent severe watershortage has generated a surge of investments with strong regional applications. The present study focuses on areas and issues outside the scope of these regional studies,aiming to provide an Australia-wide assessment of future Australian rainfall under climate change. Firstly, we unravel a process of the Indo-Pacific oceanic teleconnection and examine its role in influencing variability of the Indian Ocean, and hence Australianrainfall variations. An examination of their contribution to the warming structure of the Indian Ocean is carried out. Secondly, we explore dynamics of North West Australianrainfall variability and mechanisms of a rainfall increase over the past decades, and benchmark climate models in terms of their ability to reproduce the observed variability and trends, focusing on the role of increasing northern hemispheric aerosols in the rainfallincrease. Thirdly, we provide a dynamical explanation to the common future of a fast Tasman Sea warming rate under climate change, and identify the impacts of suchwarming on Australian rainfall. Finally, we examine the relative importance of the three systems, in addition to Tasman Sea warming, in driving rainfall changes undergreenhouse conditions. This project contributes to no less than six peer-reviewed journal publications.

On-going climate change through the 21st century projects increasingly warmer and drier conditions for Mediterranean-type ecosystems (MTEs), creating threats to species persistence in these biodiversity hotspots. For the highly biodiverse kwongan of southwest Australia, this means a climate shifting towards semi-arid conditions, yet how this unique vegetation type will respond to a novel hotter and drier climate is largely unknown. Therefore, this study examined the effects of altered rainfall and temperature on demographic processes of woody kwongan in post-fire (0 - 3 years since last fire) and mature (12 - 15 years since last fire) stands across a soil depth gradient in the northern sandplains of southwestern Australia, seeking to identify the consequences for plant species and functional trait composition. To achieve this, a selection of commonly occurring species (Banksia attenuata, Banksia hookeriana, Melaleuca leuropoma and Beaufortia elegans as primary focal species) were used to form a plant functional trait scheme, with fire-response strategy (resprouter, non-resprouter) as a trait of key interest due to the fire prone nature of MTEs, and leaf type (broad, needle, small), growth form (shrub, subshrub) and seed size (large, medium, small) as traits of interest due to their potential roles in drought and temperature responses. Passive rainout shelters were used to reduce rainfall, and drip irrigation to increase rainfall, by ~ 30 %. Open top chambers were used to increase temperature, with daytime temperature increased by an average of 2.9˚C. Seedling germination, survival and growth, and adult survival, health, flowering and fruiting were reduced by drought and warming, with increased rainfall producing little change. Greater magnitude of reduction was observed under experimental warming, however experimental drought resulted in greater level of change in functional trait composition. Despite the general higher resistance of adult resprouters, it was non-resprouters that showed potential to become the dominant fire-response strategy in a drier environment, through higher seedling resilience and similar resistance as adults to resprouters. With a decline in survival for both post-fire resprouts and seedlings, resprouters could be at risk of population decline in the long term. Subshrub and small leaf traits were the most successful in drought conditions due to their drought tolerant nature, while broad leaf and shrub traits will likely suffer population decline. In warmer conditions, significant decline in resprouter seedling survival was matched by equally large decline in non-resprouter adult survival, indicating little change in dominance of non-resprouters at the seedling stage and resprouters at the adult stage, and thus little change in their relative abundances. The needle leaf trait was most competitive in warmed conditions performing well relative to other traits both in seedlings and adults. Shallow soil profiles, reflecting lower water availability, negatively affected demographic rates, suggesting decreases in diversity and density on shallow soils as less drought tolerant species retreat to deeper soil profiles with greater water stores. Results here show potential for large scale change in MTEs in projected warmer and drier climates, through decline in vulnerable functional traits, and thus reduced density of woody species and losses to biodiversity. Further investigation is needed into the combined effect of warming and drought, in addition to impact of altered fire regime, with changes in fire behaviour projected for MTEs as a result of warmer and drier conditions. Investigation that encompasses a broader range of Mediterranean species is also necessary to provide greater accuracy to conclusions drawn here on functional trait responses.

As a global climate phenomenon, the El Ni??o-Southern Oscillation (ENSO) involves the coupling of the ocean and the atmosphere. Most climate prediction studies have, by far, only investigated the teleconnections between global climatic anomalies and the ???surface??? predictors of ENSO. The prediction models resulting from these studies have generally suffered from inadequate, if not the lack of, skill across the so-called boreal ???spring barrier???. This is illustrated in the first part of this thesis where the applicability of the SOI phase for long-lead rainfall projections in Australia is discussed. With the increasing availability of subsurface ocean temperature data, the characteristics of the Pacific Ocean???s heat content and its role in ENSO are now better understood. The second part of this thesis investigated the predictability of ENSO using the thermocline as a predictor. While the persistence and SST-based ENSO hindcasts dropped in skill across the spring barrier, the thermocline-based hindcasts remained skillful even up to a lag of eighteen months. Continuing on the favorable results of ENSO prediction, the third part of this thesis extended the use of the thermocline in the prediction of Australia???s rainfall and streamflow. When compared to models that use ???surface??? predictors, the model that incorporated thermocline information resulted in more skillful projections of rainfall and streamflow especially at long lead-times. More importantly, significant increases in skill of autumn and winter projections demonstrate the ability of the subsurface ocean to retain some climatic memory across the predictability barrier. This resilience can be attributed to the high persistence of the ocean heat content during the first half of the year. Based on weighting, the model averaging exercise also affirmed the superiority of the ???subsurface??? model over the ???surface??? models in terms of streamflow projections. The encouraging findings of this study could have far-reaching implications not only to the science of ENSO prediction but also to the more pragmatic realm of hydrologic forecasting. What this study has demonstrated is an alternative predictor that is suitable for the long range forecasting of ENSO, rainfall and streamflow. With better hydrologic forecasting comes significant improvement in the management of reservoirs which eventually leads to an increase in the reliability and sufficiency of water supply provision.

Wickepin is a low rainfall area in the south west of Australia where wheat and sheep are the dominant forms of farming. These farming systems are typical of much of south-western Western Australia where clearing of the native vegetation for farming over the last century has contributed to the onset of widespread salinity and the subsequent loss of productivity on the affected land. However, with the commencement of national carbon management legislation the Carbon Credits Energy (Carbon Farming Initiative) Act (Cth) 2011 (CFI) on July 1 2012 carbon sequestered in reforestation and soils can be brought to account and sold to emitters elsewhere in the economy. A key question is whether farmers and investors can generate profit by either (a) replanting trees on salt affected land or (b) replacing existing crops and pastures with trees. Although several authors have suggested that wide-spread carbon sequestration is possible in this and similar environments elsewhere in Australia, this is often as a result of modelling, rather than real data. Carbon sequestration was thus examined for a range of tree species in a field trial planted in 2001 at Wickepin. The data have been analysed to determine whether carbon credits could be claimed and the economic return from reforestation over a 10-year period determined. Although additional environmental service markets (e.g. paying for salinity repair, biodiversity enhancement) or other markets for forestry products (as a bioenergy feedstock, timber) are often posited, none of these markets currently exists in any depth and the analysis was undertaken for carbon value alone. The study found that although Eucalyptus occidentalis (2000 stems ha-1) had the highest carbon 10-year sequestration rate of 78.3±8.4 t CO2-e ha-1, E. sargentii (500 stems ha-1) had the most promise (economic return, survival, growth rate) with carbon sequestration at 65.1±9.7 t CO2-e ha-1, as it is less costly to establish trees at a lower planting density. These rates are similar to those predicted by Polglase et al. (2008). Assuming a carbon credit price of $23 t CO2-e-1, the return was $1498 ha-1 which translated to a rate of return of 13.4% and this is considered a good investment prospect for the treatment of saline land by farmers. For an investor considering converting existing crops or pastures to trees the returns on the trees after 10 years would have been 9.8% p.a., however the venture would be overall rendered uneconomic due to the large decrease in land value associated with such a change. In this case it was assumed that wholesale reforestation of farmland reduced other economic options for the land. Investors considering reforesting for carbon credits should thus only invest in farms that are run down or suffer major salinity which would be available at a very low price per hectare compared to profitable farms used for current agricultural production. For both a farmer and investor given that the carbon price will be allowed to fluctuate, or the CFI may be scrapped altogether, there is still risk that although the trees are planted and achieve the predicted carbon sequestration rates there may be no positive financial return. The study concludes that the CFI is an exciting opportunity to address both salinity (and indirectly biodiversity) and will in general provide an economic return on non productive farmland for existing landowners. It recommends that uncertainty with both a minimum carbon price and the continuation of the scheme be resolved before making large-scale investment.

The high rainfall zone (HRZ) of south west Western Australian (WA) has traditionally been dominated by livestock industries. However, a reduction in wool price throughout the 1990’s has stimulated a transition to farm systems that contain an increasing proportion of annual cropping enterprises. The HRZ, compared to traditional wheat belt areas of WA, has higher rainfall and a longer, cooler growing season. Potential grain yields as determined by seasonal rainfall are not often achieved because of inadequate nutrition and other constraints such as water-logging and disease. Substantial research has been conducted in the HRZ focusing on increasing grain yield to limits set by seasonal rainfall. Research on wheat grain quality characteristics, however, has been limited. The aim of this research was to examine the influence of cultivar, environment and nutrition management on wheat quality characteristics in the HRZ of south west WA and to examine the stability of cultivar performance in relation to site and season.A series of experiments was grown at Moora and Williams in 2005, 2006 and 2007. Sites were chosen to represent contrasting environments within the HRZ. Moora, the more northern site typically has higher temperatures and lower rainfall compared to Williams. Eight cultivars were selected, two that are accepted into each of the commercial quality grades (Australian Prime Hard APH, Australian Hard AH, Australian Premium White APW and Durum). Three levels of nutrition management were applied ‘control’, ‘grower’ and ‘researcher’ and were chosen to simulate low, medium and high fertiliser rates likely to be used by growers in the HRZ. Treatments effects were measured for grain yield, physical grain quality characteristics and grain protein quality charactertics as determined by a mixograph.Environment was responsible for almost 90% of the variation for grain yield, screenings, Hagberg falling number and milling yield. Management of crop nutrition was the principal source of variation for grain protein quantity (48%), dough strength as measured by mixograph area below the curve (52%) and water absorption (46%-52%). It was often the second greatest source of variation for other characteristics measured in this study. Cultivar was the predominant source of variation for dough strength as measured by mixograph initial build-up (46%) and dough stability (47%), but it had only a small affect on grain yield and grain protein quantity (2%).The increase in nutrition resulted in a significant increase in water absorption and dough strength and a trend towards increasing dough stability. An increase in gliadin and glutenin proteins is thought to be responsible for this result. The low nutritional status of soils in the HRZ not only restricts grain yield but grain protein quantity and quality. The impact of nutrition management on grain yield and quality characteristics as shown in these experiments should be considered by breeders, agronomists and marketers when interpreting experimental results. Furthermore, the results indicate that the nutritional management of breeding experiments should be based on a sound methodical approach, incorporating a combination of soil test results, grain yield potential and seasonal monitoring for the environment in question and not be simply based on levels that are either ‘district practice’ or ‘non-limiting’.This study has also identified statistically significant differences between cultivars for stability of grain yield and grain protein quality. Four cultivars (three bread wheat and one durum wheat) were characterised as having dynamic stability, which is described as the ability to respond to an environment in a predictable way. In addition, three cultivars were assessed as having static stability, unchanged performance regardless of any variation in environment for water absorption. This information indicates that assessment of stability of cultivars during the early stages of testing can assist commercial buyers in sourcing suitable grain quality and even that there may be potential to breed cultivars with improved static or dynamic stability.If it is assumed that the Australian wheat industry cannot compete in a global wheat market based on the relatively small level of production. Then the future of the industry lies in producing the qualities required by specific markets. Realizing the impact of nutrition management on quality characteristics in the HRZ of WA will be a positive step towards a sustainable industry.

Copy of author's previously published work inserted. Bibliography: leaves 261-306. The objectives of the project were: i. to determine whether there are competitive interactions between Aporrectodea trapezoides and A. caliginosa and A. rosea.--ii. to investigate compeditive interactions between A. calignosa, Microscolex dubius and A. trapezoides.--iii . to determine the likely impact of A. longa on soil fauna, especially the native earthworm, Gemascolex lateralis, in native ecosystems.

A remote sensing study of global and Australian cloud cover was undertaken using a combination of High-resolution Infrared Radiation Sounder (HIRS) and MODerate-resolution Imaging Spectroradiometer (MODIS) data for a 31-year period (1985 to 2015). Regional characterisations of potential rain clouds were investigated in the Southwest and Kimberley regions of Western Australia using satellite-derived cloud physical and micro-physical properties (cloud top pressure, cloud effective emissivity, cloud top temperature, cloud optical thickness and cloud effective radius).

This thesis presents the development and application of a downscaling framework for multi site simulation of daily rainfall. The rainfall simulation is achieved in two stages. First, rainfall occurrences at multiple sites are downscaled, which is followed by the generation of daily rainfall amounts at each site identified as wet. A continuous weather state based nonparametric downscaling model conditional on atmospheric predictors and a previous day average rainfall state is developed for simulation of multi site rainfall occurrences. A nonparametric kernel density approach is used for simulation of rainfall amounts at individual sites conditional on atmospheric variables and the previous day rainfall amount. The proposed model maintains spatial correlation of rainfall occurrences by simulating concurrently at all stations and of amounts by using random innovations that are spatially correlated yet serially independent. Temporal dependence is reproduced in the occurrence series by conditioning on previous day average wetness fraction and assuming the weather states to be Markovian, and in the amount series by conditioning on the previous day rainfall amount. The seasonal transition is maintained by simulating rainfall on a day-to-day basis using a moving window formulation. The developed downscaling framework is calibrated using the relevant atmospheric variables and rainfall records of 30 stations around Sydney, Australia. Results indicate a better representation of the spatio-temporal structure of the observed rainfall as compared to existing alternatives. Subsequently, the framework is applied to predict plausible changes in rainfall in warmer conditions using the same set of atmospheric variables for future climate obtained as a General Circulation Model simulation. While the case studies presented are restricted to a specific region, the downscaling model is designed to be useful in any generic catchment modelling and management activity and/or for investigating possible changes that might be experienced by hydrological, agricultural and ecological systems in future climates.

[Truncated abstract] Generally hydrologic and ecologic models operate on arbitrary time and space scales, selected by the model developer or user based on the availability of field data. In reality rainfall is highly variable not only annually, seasonally and monthly but also the intensities within a rainfall event and infiltration properties on semi-arid hillslopes can also be highly variable as a result of discontinuous vegetation cover that form mosaics of areas with vegetation and areas of bare soil. This thesis is directed at improving our understanding of the impacts of the temporal representation of rainfall and spatial heterogeneity on model predictions of hydrologic thresholds and surface runoff coefficients on semi-arid landscapes at the point and hillslope scales. We firstly quantified within storm rainfall variability across a climate gradient in Western Australia by parameterizing the bounded random cascade rainfall model with one minute rainfall from 15 locations across Western Australia. This study revealed that rainfall activity generated in the tropics had more within storm variability and a larger proportion of the storm events received the majority of rain in the first half of the event. Rainfall generated from fontal activity in the south was less variable and more evenly distributed throughout the event. Parameters from the rainfall analysis were then used as inputs into a conceptual point scale surface runoff model to investigate the sensitivity of point scale surface runoff thresholds to the resolution of rainfall inputs. This study related maximum infiltration capacities to average storm intensities (k*) and showed where model predictions of infiltration excess were most sensitive to rainfall resolution (ln k* = 0.4) and where using time averaged rainfall data can lead to an under prediction of infiltration excess and an over prediction of the amount of water entering the soil (ln k* > 2). For soils susceptible to both infiltration excess and saturation excess, total runoff sensitivity was scaled by relating drainage coefficients to average storm intensities (g*) and parameter ranges where predicted runoff was dominated by infiltration excess or saturation excess depending on the resolution of rainfall data were determined (ln g* <2). The sensitivity of surface runoff predictions and the influence of specific within storm properties were then analysed on the hillslope scale. '...' It was found that using the flow model we still get threshold behaviour in surface runoff. Where conditions produce slow surface runoff velocities, spatial heterogeneity and temporal heterogeneity influences hillslope surface runoff amounts. Where conditions create higher surface runoff velocities, the temporal structure of within storm intensities has a larger influence on runoff amounts than spatial heterogeneity. Our results show that a general understanding of the prevailing rainfall conditions and the soil's infiltration capacity can help in deciding whether high rainfall resolutions (below 1 h) are required for accurate surface runoff predictions. The results of this study can be considered a contribution to understanding the way within storm properties effect the processes on the hillslope under a range of overall storm, slope and infiltration conditions as well as an improved understanding of how different vegetation patterns function to trap runoff at different total vegetation covers and rainfall intensities.

The honey possum Tarsipes rostratus is a tiny (7 - 12 g) highly specialised flower-feeding marsupial endemic to the south-western corner of Australia. The impact of fire on this small mammal was studied, over a 19-year period, in the Fitzgerald River National Park, a large (330,000 ha) area of relatively undisturbed heathland/shrubland, rich in the proteaceous and myrtaceous plants upon which the honey possum appears to rely for food. The honey possum is the most abundant and widespread mammal in this Park. Capture rates of honey possums were significantly related to the years since the vegetation was last burnt, annual rainfall in the preceding (but not the current) year, the season when trapping occurred, and the trapping grid operated. Capture rates declined markedly after fire and remained low (less than one third of those in long unburnt vegetation) for about 4 - 5 years following a fire. Rates of capture then increased steadily over the next 20 - 25 years, with maximal abundance recorded about 30 years after fire. Thereafter, there appeared to be a slight decline in capture rates, but even in the vegetation unburnt for longest (> 50 years since fire), honey possum abundance was substantial and relatively stable. In contrast to these changes in abundance, the structure of the honey possum population, with 79 % adults and 57 % males, appeared little influenced by fire history, annual rainfall, season or grid. The increase in the rates of capture of honey possums following fire paralleled the pattern of availability of cover in the vertical and, to a lesser extent, horizontal plane. Indeed, projective foliage cover took around 20 years after fire to reach levels similar to those available in areas unburnt for even longer. The trend in capture rates was also congruent with the maturation of the most frequently visited foodplants of honey possums, particularly Banksia nutans (summer flowering) and B. baueri (winter flowering). Areas long unburnt still contained shelter and foodplants adequate for honey possums even 50 years or more after fire, with only slight evidence of senescence. Pollen loads indicated that honey possums caught in burnt areas, where their preferred foodplants were absent, continued to feed on these favoured foodplants (Banksia and Dryandra spp.) at nearby unburnt areas. In addition, they also fed, in both burnt and long unburnt areas, upon a suite of other plant species that regenerated more rapidly from lignotubers and epicormic buds, as well as from seeds (e.g. Eucalyptus and Calothamnus spp.). Thus, honey possums appeared to persist with their preferences for feeding from a limited number of flowering plants despite some of these species not being available in recently burnt areas for many years. Nearby patches of unburnt vegetation can clearly be important refuges, feeding grounds and shelter for the few honey possums that visit recently burnt areas, and appear to be the source of honey possum colonists in the years following a fire. Capture rates were also greater following years when rainfall was higher than average. Indeed, rainfall had as great an influence upon capture rates as time since fire. Capture rates were also consistently higher over winter, and to a lesser extent over summer, than in either autumn or spring. Individual grids, even those close together in apparently similar vegetation with a similar fire history, still differed significantly overall in their capture rates of honey possums. This last finding has implications for the use of chronosequences in the study of post-fire changes in biota. Although not the primary focus of the study, data on the limited suite of other, far less abundant, small mammals present indicated that house mouse Mus musculus domesticus numbers peak soon after fire (about two years after fire), grey-bellied dunnart Sminthopsis griseoventer numbers somewhat later (about eight years after fire) and that southern bush rats Rattus fuscipes fiuscipes, like honey possums, are later successional species. Most species were present in vegetation over a range of post-fire ages, with data consistent with models based on sequential changes in relative abundance. Like many Australian mammals, the range of the honey possum has contracted substantially over the last 200 years and the coastal heathlands of the south-west are its last stronghold. In terms of its conservation, this study indicates that, if possible, management burns in these heathlands should be separated by intervals of at least 20 years between successive burns, and preferably even longer. If burns are required more frequently to meet other management priorities, it is highly preferable that they are small and patchy, rather than large scale. Such practices may help ensure the long-term survival of this unique, highly specialised and endemic marsupial.

The aim of this study was to gain a better understanding of the conditions that lead to the mite Balaustium medicagoense to cause crop damage and to develop sustainable management strategies. The main factor that influences B. medicagoense abundance is the presence of plant hosts between cropping seasons. Management strategies need to rely on cultural controls such as decreasing available plant hosts, using cropping rotations to suppress mite populations as chemical control options are limited

The ground-dwelling invertebrate fauna of medium rainfall jarrah forest was surveyed in three forest blocks (Kingston, Warrup and Winnejup) approximately 25 km north-east of Manjimup in the south-west of Western Australia. Invertebrates were collected by means of pitfall traps on 18 sampling occasions over a period of 22 months (May 1994-March 1996). Approximately 500 000 invertebrates were collected from thirty-five Classes, sub Classes or Orders. The Blattodea, Orthoptera and Araneae were further identified to morphospecies and males and females were distinguished. The forest litter invertebrate community was dominated by Collembola (springtails) (60.8% of total abundance), the Formicidae (ants) (16.8%), Diptera (flies) (6.1%) Coleoptera (beetles) (4.7%) Apocrita (wasps), (2.8%), Araneae (spiders) (2.6%) Acarina (mites) (2.0%) Hemiptera (true bugs) (1.4%) Blattodea (cockroaches) (0.4%) and Orthoptera (crickets and grasshoppers) (0.4%). These accounted for 98% of the total abundance. Of the three taxa identified to morphospecies, spiders were the most diverse, with 31 families and 108 morphospecies present, followed by the grasshoppers and crickets with 3 subfamilies and 67 morphospecies and the cockroaches with 4 families and 32 morphospecies. Six arachnid families (the Actinopidae, Idiopidae, Micropholcommatidae, Nemesiidae, Orsolobidae and Toxopidae) with Gondwanan affinities were present. Marked seasonal trends were present, with overall invertebrate activity (excluding Collembola) highest during spring and lowest during winter. The main factors affecting activity were temperature and rainfall. Changes in the numerical dominance of the taxa occurred between seasons and between years. Marked spatial variability was also evident and appeared to be associated with changes in microclimatic conditions and small-scale spatial variations in habitat. The responses of these invertebrate communities to timber harvesting practices (clearing without post-harvest burn) were examined as part of a larger integrated study (the Kingston Project) conducted by the Western Australian Department of Conservation and Land Management (CALM). A modified BACI (Before/After Control/Impact) design was used. Twenty sites, 8 Internal Controls, 4 External Controls and 8 Impact sites were sampled simultaneously before and after logging. Sampling was undertaken on 8 occasions prior to logging and 10 following logging. Logging occurred between March and April 1995. No significant impacts on total invertebrate abundance and richness were observed after logging. Moreover, only five taxa, Blattodea, Coleoptera, Diptera, Hemiptera and Orthoptera, showed significant changes in abundance, with Blattodea being the most severely affected. Impacts detected by ordination were also of short duration, with post-logging communities resembling those of undisturbed sites after 10 months. Retrospective power analysis revealed that the experimental design used had sufficient power (0.8+) to detect a 30-40% change in total invertebrate abundance. Moreover, the design had power to detect changes of 10-50% for most taxa. Identification of three taxa to morphospecies revealed significant effects of logging, not only on the taxa found to be sensitive to this disturbance (Blattodea and Orthoptera), but also in Araneae, which had shown no impacts at the level of Order. However, for spiders at least, identification to the level of family was preferable to morphospecies as the impacts of logging were masked by environmental noise at those resolutions. The impact of logging on these assemblages was also only of a short duration. Logged sites followed the same seasonal patterns as control sites in the ordination plots, indicating that seasonal and inter-annual climatic changes appear to be more important determinants of community structure and function than a logging event.

Issues arising from climate change and long-term natural climate variability have become the focus of much recent research. In this study, we specifically explore the impacts of long-term climate variability and climate changes upon flood frequencies. The analyses of the flood frequencies are carried out in a comparative manner in catchments located in semiarid-temperate and tropical landscapes in Australia, namely Perth, Newcastle and Darwin, using a process-based derived flood frequency approach. The derived flood frequency analyses are carried out using deterministic rainfall-runoff models that capture the intrinsic water balance variability in the study catchments, and driven by temporal rainfall event sequences that are generated by a stochastic rainfall model that incorporates temporal variabilities over a multiplicity of time scales, ranging from within-event, between-event to seasonal, multi-annual and multi-decadal time scales. Six climate scenarios are considered for Newcastle, that combine the ENSO (El Niño Southern Oscillation) and IPO (Inter-decadal Pacific Oscillation) modes of variability, and six different climate scenarios are considered for Perth and Darwin that combine these different ENSO modes and step changes in climate (upwards or downwards) that occurred in 1970 in both regions, which were identified through statistical analysis. The results of the analyses showed that La Niña years cause higher annual maximum floods compared to El Niño and Neutral years in all three catchments. The impact of ENSO on annual maximum floods in the Newcastle catchment is enhanced when the IPO is negative and for Perth, the impact of ENSO weakens in the post-1970 period, while it strengthens in Darwin in the same period. In addition, the results of sensitivity and scenario analyses with the derived flood frequency model explored the change of dominant runoff generation processes contributing to floods in each of the study catchments. These analyses highlighted a switch from subsurface stormflow to saturation excess runoff with a change of return period, which was much more pronounced in Perth and Darwin, and not so in Newcastle. In Perth and Darwin this switch was caused by the interactions between the out-of-phase seasonal variabilities of rainfall and potential evaporation, whereas the seasonality was much weaker in Newcastle. On the other hand, the combination of higher rainfall intensities and shallower soil depths led to saturation excess runoff being the dominant mechanism in Newcastle across the full range of return periods. Consequently, within-storm rainfall intensity patterns were important in Newcastle in all major flood producing events (all return periods), where they were only important in Perth and Darwin for floods of high return periods, which occur during wet months in wet years, when saturation excess runoff was the dominant mechanism. Additionally, due to the possibility of a change of process from subsurface stormflow to saturation excess when conditions suited this switch, the estimates of flood frequency are highly uncertain especially at high return periods (in Darwin and Perth) and much less in Newcastle (when no process change was involved).

The southwest of Western Australia (SWWA) is an area of significant agricultural production and an internationally recognised biodiversity hotspot. The region has experienced marked rainfall reductions over the last four decades and there is uncertainty as to the extent of future changes to the hydrological regime. Hence, there is a need for regional climate information in SWWA to better inform climate adaptation strategies for several key sectors, including agriculture and forestry. The overarching aim of this project is to provide such information, with a focus on changes in rainfall and temperature extremes. The Weather Research and Forecasting (WRF) model was used as a regional climate model for SWWA. Given the known sensitivity of WRF to physics options and driving data, the most appropriate physical parameterisations were tested on a yearly time-scale. Based on these findings, a 30-year climatology was produced for SWWA (1981-2010) at a 5 km resolution by downscaling ERA-Interim reanalysis. Comparisons against observations showed that the model was able to simulate the daily, seasonal and annual variation of temperature and precipitation well, including extreme events. The model was then used to downscale an ensemble of 4 general circulation models (GCMs) for the historical period (1970- 1999) and compared against both observations and the GCMs. WRF was shown to add value to the GCM data for 3 out of the 4 GCMs evaluated, particularly in the spatio-temporal distribution of winter rainfall. Finally, the ensemble was run from 2030-2059 to examine projected climate change in SWWA. Results project that maximum temperature extremes will increase, consistent with mean changes however the variance of maximum temperatures is not projected to change significantly. While mean minimum temperatures are not projected to increase as much as maximum temperatures, there is strong evidence that the variability of minimum temperatures will increase. This has the potential to raise the likelihood of night time temperature extremes. Simulations project a reduction in rainfall, particularly during winter. This decline is related to fewer frontal systems traversing the SWWA and hence fewer rain days. The study found no evidence to suggest that the intensity of rain bearing winter storms is likely to change.

1 v.
Title page, contents and abstract only. The complete thesis in print form is available from the University Library.
Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, Waite Agricultural Research Institute, 1992

Legumes play an integral role in increasing agricultural productivity, particularly in low input agricultural systems in Australia, due to their ability to form symbiotic interactions with a group of soil bacteria called rhizobia. However, in medium-to-low rainfall areas of southern Australia, there is a lack of suitable annual pasture legumes, which is limiting agricultural productivity and profitability in these farming systems. Scorpiurus muricatus is an annual legume from the Mediterranean which possesses high nutritive value and palatability for livestock, is high yielding, capable of self-seeding and is well-adapted to hot and dry summers. As such, S. muricatus is currently being evaluated as a new pasture legume for southern Australia. Crucial to the success of introducing this legume will be the availability of a highly effective rhizobial inoculant strain. This thesis therefore sought to characterise the phylogeny, free-living and symbiotic phenotype of a range of bacteria isolated from Scorpiurus spp. A total of 19 strains were investigated, with 16s rRNA sequencing demonstrating that 18 of these strains belonged to the genus Mesorhizobium, with the remaining strain (WSM1184) most closely related to Agrobacterium tumefaciens. Analysis of nifH and nodC symbiosis genes further showed that the characterised Mesorhizobium strains generally shared highly similar sequences for these loci, indicating a comparatively high degree of genetic similarity. In particular, WSM1343 (isolated from Scorpiurus sulcatus growing in Morocco) and WSM1386 (isolated from S. sulcatus in Manjimup, Western Australia) were shown to share highly similar symbiosis genes, but divergent 16S rRNA genes, suggesting the possibility that these strains may contain symbiosis genes on mobile Integrative and Conjugative Elements (ICEs). While the temperature tolerance and apparent optimum growth temperature of the test strains of 28°C was consistent with that commonly reported for Mesorhizobium spp., their growth rate was atypical for this genus, with 15 of the 18 strains having a growth rate on YMA at 28°C slower than that generally described for Mesorhizobium. This slower growth rate may be a common feature of rhizobia from S. muricatus nodules and therefore should be considered when isolating organisms from this legume. Symbiotic effectiveness experiments showed all Mesorhizobium strains nodulated S. muricatus and fixed N2 on this host, with the most effective strain producing 67.5% of the mean shoot dry weight of the N-fed control plants. Host range experiments demonstrated a subset of the Mesorhizobium strains nodulate existing Australian commercial pasture legumes Biserrula pelecinus and Lotus corniculatus, with the effectiveness data suggesting these strains fix N2 poorly on both hosts. In contrast, none of the strains tested were able to nodulate the grain legume Cicer arietinum. While this thesis has characterised the phylogeny, free-living and symbiotic phenotype of a range of S. muricatus microsymbionts, further work is required before a suitable commercial inoculant strain can be recommended for this pasture legume. First, all the strains tested in this thesis were isolated from S. sulcatus plants or soils with Scorpiurus spp. present, rather than S. muricatus and it is not known whether strains from either species are cross-compatible for effective N2 fixation. Future studies may therefore locate more effective N2-fixing rhizobia for S. muricatus by isolating microsymbionts from this host in the field. Second, experiments testing the ability of commercial inoculants for already-established pasture legumes B. pelecinus (WSM1497), Lotus sp. (SU343, CC829) and the grain legume C. arietinum (CC1192) to nodulate and fix N2 on S. muricatus need to be conducted to determine whether these inoculants will interact with this legume. Finally, the data strongly suggest that S. muricatus-nodulating Mesorhizobium spp. may contain symbiosis genes on mobile symbiosis ICEs. Given that the phenomenon of ICE transfer has led to the evolution of poorly effective microsymbionts for B. pelecinus, it is imperative that these S. muricatus strains be interrogated for the presence and transfer of symbiosis ICEs, in order to manage this mobility in any future commercial inoculant strain that is released for this pasture legume species.

Water resources management in the Pilbara region of Western Australia is vital to industry, economy and the environment. This dissertation has aimed to develop a comprehensive hydrological and hydrogeological assessment of water resources in the Yandi mine area located in the Weeli Wolli Creek catchment in the Pilbara. Water resources in this area have become increasingly vulnerable due to growing demand. Climate conditions, geology and hydrogeology, streamflow and the groundwater system of the study area were assessed. Lumped, data-driven and numerical models were employed to develop an understanding of the available surface water and groundwater resources. Three equations were derived showing the rainfall-runoff relationship within Weeli Wolli Creek catchment and subsequent modelling was undertaken for more hydrology system evaluation. Artificial Neural Networks (ANNs) and IHACRES models were used to simulate the Marillana Creek streamflow discharge, upstream of Yandi. The results suggested that ANN models perform better for a complex catchment hydrological system, compared to IHACRES model. A VISUAL MODFLOW model was used to investigate the groundwater system and its trend in the Yandi area. The model helped to understand the groundwater responses to future development with various pumping strategies and climate conditions. The scenario analysis assisted identification of zones vulnerable to a significant decline in groundwater level in response to dewatering. The analysis indicated that the maximum water level drawdown of 25m occurred in the aquifer from maximum annual pumping of 23GL. With respect to groundwater yield in particular, abstraction has a more direct impact on the groundwater system compared to climate change. The recharge into the groundwater was estimated from the fluctuations of groundwater level, groundwater modelling and water balance method. The estimated recharge from these methods was comparable and consistent within 3 to 5% of rainfall. This suggests that direct rainfall infiltration is less, compared to localised infiltration. Two new equations, applicable to Australian conditions, were developed to estimate potential evapotranspiration (ET0). These equations form a part of the water balance equation for groundwater recharge estimation. An artificial intelligent model, based on the Honey-Bee Mating Optimization algorithm (HBMO), was introduced to calibrate the new ET0 equations. The newly developed equations had better performances than available popular equations. The results of this study showed that the water resources in Yandi are considerably affected by progressing activities and their associated water requirements. A combination of multiple water assessments and modellings suggested that it is feasible to predict future access to surface water as a function of its influencing factors such as climate condition and mining activities. Scenario analysis in groundwater assessment suggested possible alternative future dewatering strategies in the Yandi mine area. The possible groundwater level recovery time is estimated to be one hundred years, which indicates this resource may not be a reliable option in future. Hydrological water balance analysis also indicated that the available surface water volume would decrease to half upon cease of discharge due to closure of mines in the study area, which is controversial condition for future water management. This research can lead to the implementation of a sustainable water resources plan, and development of appropriate strategies.

As the world’s population is growing, so is the demand for agricultural products. However, natural nitrogen (N) fixation and phosphorus (P) availability cannot sustain the rising agricultural production, thus, the application of N and P fertilisers as additional nutrient sources is common. It is those anthropogenic activities that can contribute high amounts of organic and inorganic nutrients to both surface and groundwaters resulting in degradation of water quality and a possible reduction of aquatic life. In addition, runoff and sewage from urban and residential areas can contain high amounts of inorganic and organic nutrients which may also affect water quality. For example, blooms of the cyanobacterium Lyngbya majuscula along the coastline of southeast Queensland are an indicator of at least short term decreases of water quality. Although Australian catchments, including those with intensive forms of land use, show in general a low export of nutrients compared to North American and European catchments, certain land use practices may still have a detrimental effect on the coastal environment. Numerous studies are reported on nutrient cycling and associated processes on a catchment scale in the Northern Hemisphere. Comparable studies in Australia, in particular in subtropical regions are, however, limited and there is a paucity in the data, in particular for inorganic and organic forms of nitrogen and phosphorus; these nutrients are important limiting factors in surface waters to promote algal blooms. Therefore, the monitoring of N and P and understanding the sources and pathways of these nutrients within a catchment is important in coastal zone management. Although Australia is the driest continent, in subtropical regions such as southeast Queensland, rainfall patterns have a significant effect on runoff and thus the nutrient cycle at a catchment scale. Increasingly, these rainfall patterns are becoming variable. The monitoring of these climatic conditions and the hydrological response of agricultural catchments is therefore also important to reduce the anthropogenic effects on surface and groundwater quality. This study consists of an integrated hydrological–hydrochemical approach that assesses N and P in an environment with multiple land uses. The main aim is to determine the nutrient cycle within a representative coastal catchment in southeast Queensland, the Elimbah Creek catchment. In particular, the investigation confirms the influence associated with forestry and agriculture on N and P forms, sources, distribution and fate in the surface and groundwaters of this subtropical setting. In addition, the study determines whether N and P are subject to transport into the adjacent estuary and thus into the marine environment; also considered is the effect of local topography, soils and geology on N and P sources and distribution. The thesis is structured on four components individually reported. The first paper determines the controls of catchment settings and processes on stream water, riverbank sediment, and shallow groundwater N and P concentrations, in particular during the extended dry conditions that were encountered during the study. Temporal and spatial factors such as seasonal changes, soil character, land use and catchment morphology are considered as well as their effect on controls over distributions of N and P in surface waters and associated groundwater. A total number of 30 surface and 13 shallow groundwater sampling sites were established throughout the catchment to represent dominant soil types and the land use upstream of each sampling location. Sampling comprises five rounds and was conducted over one year between October 2008 and November 2009. Surface water and groundwater samples were analysed for all major dissolved inorganic forms of N and for total N. Phosphorus was determined in the form of dissolved reactive P (predominantly orthophosphate) and total P. In addition, extracts of stream bank sediments and soil grab samples were analysed for these N and P species. Findings show that major storm events, in particular after long periods of drought conditions, are the driving force of N cycling. This is expressed by higher inorganic N concentrations in the agricultural subcatchment compared to the forested subcatchment. Nitrate N is the dominant inorganic form of N in both the surface and groundwaters and values are significantly higher in the groundwaters. Concentrations in the surface water range from 0.03 to 0.34 mg N L..1; organic N concentrations are considerably higher (average range: 0.33 to 0.85 mg N L..1), in particular in the forested subcatchment. Average NO3-N in the groundwater has a range of 0.39 to 2.08 mg N L..1, and organic N averages between 0.07 and 0.3 mg N L..1. The stream bank sediments are dominated by organic N (range: 0.53 to 0.65 mg N L..1), and the dominant inorganic form of N is NH4-N with values ranging between 0.38 and 0.41 mg N L..1. Topography and soils, however, were not to have a significant effect on N and P concentrations in waters. Detectable phosphorus in the surface and groundwaters of the catchment is limited to several locations typically in the proximity of areas with intensive animal use; in soil and sediments, P is negligible. In the second paper, the stable isotopes of N (14N/15N) and H2O (16O/18O and 2H/H) in surface and groundwaters are used to identify sources of dissolved inorganic and organic N in these waters, and to determine their pathways within the catchment; specific emphasis is placed on the relation of forestry and agriculture. Forestry is predominantly concentrated in the northern subcatchment (Beerburrum Creek) while agriculture is mainly found in the southern subcatchment (Six Mile Creek). Results show that agriculture (horticulture, crops, grazing) is the main source of inorganic N in the surface waters of the agricultural subcatchment, and their isotopic signature shows a close link to evaporation processes that may occur during water storage in farm dams that are used for irrigation. Groundwaters are subject to denitrification processes that may result in reduced dissolved inorganic N concentrations. Soil organic matter delivers most of the inorganic N to the surface water in the forested subcatchment. Here, precipitation and subsequently runoff is the main source of the surface waters. Groundwater in this area is affected by agricultural processes. The findings also show that the catchment can attenuate the effects of anthropogenic land use on surface water quality. Riparian strips of natural remnant vegetation, commonly 50 to 100 m in width, act as buffer zones along the drainage lines in the catchment and remove inorganic N from the soil water before it enters the creek. These riparian buffer zones are common in most agricultural catchments of southeast Queensland and are indicated to reduce the impact of agriculture on stream water quality and subsequently on the estuary and marine environments. This reduction is expressed by a significant decrease in DIN concentrations from 1.6 mg N L..1 to 0.09 mg N L..1, and a decrease in the �15N signatures from upstream surface water locations downstream to the outlet of the agricultural subcatchment. Further testing is, however, necessary to confirm these processes. Most importantly, the amount of N that is transported to the adjacent estuary is shown to be negligible. The third and fourth components of the thesis use a hydrological catchment model approach to determine the water balance of the Elimbah Creek catchment. The model is then used to simulate the effects of land use on the water balance and nutrient loads of the study area. The tool that is used is the internationally widely applied Soil and Water Assessment Tool (SWAT). Knowledge about the water cycle of a catchment is imperative in nutrient studies as processes such as rainfall, surface runoff, soil infiltration and routing of water through the drainage system are the driving forces of the catchment nutrient cycle. Long-term information about discharge volumes of the creeks and rivers do, however, not exist for a number of agricultural catchments in southeast Queensland, and such information is necessary to calibrate and validate numerical models. Therefore, a two-step modelling approach was used to calibrate and validate parameters values from a near-by gauged reference catchment as starting values for the ungauged Elimbah Creek catchment. Transposing monthly calibrated and validated parameter values from the reference catchment to the ungauged catchment significantly improved model performance showing that the hydrological model of the catchment of interest is a strong predictor of the water water balance. The model efficiency coefficient EF shows that 94% of the simulated discharge matches the observed flow whereas only 54% of the observed streamflow was simulated by the SWAT model prior to using the validated values from the reference catchment. In addition, the hydrological model confirmed that total surface runoff contributes the majority of flow to the surface water in the catchment (65%). Only a small proportion of the water in the creek is contributed by total base-flow (35%). This finding supports the results of the stable isotopes 16O/18O and 2H/H, which show the main source of water in the creeks is either from local precipitation or irrigation waters delivered by surface runoff; a contribution from the groundwater (baseflow) to the creeks could not be identified using 16O/18O and 2H/H. In addition, the SWAT model calculated that around 68% of the rainfall occurring in the catchment is lost through evapotranspiration reflecting the prevailing long-term drought conditions that were observed prior and during the study. Stream discharge from the forested subcatchment was an order of magnitude lower than discharge from the agricultural Six Mile Creek subcatchment. A change in land use from forestry to agriculture did not significantly change the catchment water balance, however, nutrient loads increased considerably. Conversely, a simulated change from agriculture to forestry resulted in a significant decrease of nitrogen loads. The findings of the thesis and the approach used are shown to be of value to catchment water quality monitoring on a wider scale, in particular the implications of mixed land use on nutrient forms, distributions and concentrations. The study confirms that in the tropics and subtropics the water balance is affected by extended dry periods and seasonal rainfall with intensive storm events. In particular, the comprehensive data set of inorganic and organic N and P forms in the surface and groundwaters of this subtropical setting acquired during the one year sampling program may be used in similar catchment hydrological studies where these detailed information is missing. Also, the study concludes that riparian buffer zones along the catchment drainage system attenuate the transport of nitrogen from agricultural sources in the surface water. Concentrations of N decreased from upstream to downstream locations and were negligible at the outlet of the catchment.

This thesis presents three essays on the analysis of historical meteorological data in Australia. The Australian Bureau of Meteorology has established a network of more than one thousand stations across Australia that have recordings dating from early last century, resulting in a large dataset of meteorological records. These data provide important information on the dynamics of the Australian climate system and systematic investigation using these data can help us to better understand our climate and prepare for possible changes. The purpose of this thesis is to develop models and methods to analyse such meteorological data from a statistical perspective. In Chapter 2, a spatia-temporal model is developed based on monthly average temperature data at 177 locations in south-eastern Australia over 40 years. Guided by a preliminary analysis, a model with components dealing with spatial varying mean and seasonality, short-term and long-term temporal trends is built, and the space-time interaction is modelled by the kernel-convolution method. It is shown that the temperature has become warmer in most of the south-eastern Australia during the period under investigation. In Chapter 3, a new duration-dependent Hidden Markov Model is proposed as an extension to the Hidden Markov Model (HMM) and Non-homogeneous Hidden Markov Model (NHMM) which assumes that the transition probabilities are either constant or only depend on some independent variables. The possibility of duration-dependent effects is formally considered in this chapter where the transition probabilities are allowed to be explicitly correlated to duration - how long the hidden system has been in the current state. This approach is used to model the amount of daily rainfall amount at 5 locations in Darwin, Northern Territory. For data arising from climate phenomenon, such as the temperature and rainfall data considered here, it is common for outliers to be present. The presence of outliers could unduly influence the results of any analysis that are conducted and make conclusion non-robust. But it is often difficult to detect them simultaneously because of the masking effect. Motivated by this problem, a general method is proposed in Chapter 4 for identifying multiple influential observations in regression models. The ability of this method is tested and illustrated by both a thorough simulation and several examples.

Research Doctorate - Doctor of Philosophy (PhD)
Water resources management relies on hydrological (or rainfall runoff (R-R)) models. These models are typically used with an implicit assumption that hydrological processes and catchment characteristics are stationary. However, state-of-the-art R-R and eco-hydrological models (including the Australian Water Resources Assessment (AWRA) and the Source modelling platform) have been found to overestimate runoff during multi-year droughts in Southeast Australia (SEA), especially when calibrated during non-dry epochs. Therefore, it is necessary to identify the reasons why R-R models fail to realistically simulate runoff in catchments associated with non-stationarity in climate and/or catchment conditions. In this thesis, mechanisms governing both the annual and seasonal scale non-stationarity in R-R relationships were evaluated for two heterogeneous catchments in the SEA. The mechanisms evaluated were selected from the literature and were categorised into endogenous and exogenous (climate associated) catchment mechanisms. The results show that groundwater (GW) table (and associated surface water (SW)-GW interactions), baseflow (sub-surface water flow) and Leaf Area Index (LAI) (a proxy for vegetation cover) are the main endogenous catchment mechanisms which govern R-R non stationarity at both annual and seasonal scales. For exogenous catchment mechanisms, maximum temperature (T_max), rainfall and potential evapotranspiration (ET₀) are found to be the most influential on R-R non-stationarity at annual and seasonal scales. These insights into important endogenous and exogenous catchment mechanisms were then supplemented by an investigation into which R-R model performs best under hydroclimatic variability and non-stationarity for the two study catchments in SEA. Multiple criteria analysis was used to decide on three R-R models (a conceptually lumped model (IHACRES), a process-based semi-distributed model (HEC-HMS) and a fully-distributed model (SWATgrid)) to compare under contrasting hydroclimatic conditions (Average1, Average2, Dry1, Dry2, Wet1 and Wet2 conditions). The models were calibrated for the Average1, Dry1 and Wet1 epochs and validated for Average2, Dry2 and Wet2 epochs for each calibration epochs. It was found that while SWATgrid model realistically simulates runoff at the smaller catchment for calibration/validation during the Average1 and Wet1 epochs. None of the models realistically simulate runoff under any climatic epoch in the larger catchment. This highlights the knowledge gap already mentioned, that existing R-R models do not realistically simulate runoff in catchments associated with non-stationarity in hydroclimatic conditions. In theory, a semi- or fully-distributed R-R model should account for mechanisms governing non-stationarity in R-R relationships. However, this is obviously not happening and it is hypothesised that a reason for this is the lack of realistic representation of SW-GW interactions in current R-R models. Therefore, in order to address this, a linked SW-GW modelling approach was developed and tested in the two study catchments. The linked SW-GW modelling approach couples a SW (or R-R) model (which is SWATgrid as it was identified to be the best performing model under hydroclimatic variability) and a GW model (MODFLOW, chosen based on multiple criteria analysis). First, SWATgrid was calibrated using its integrated GW approach of lumped baseflow components (stand-alone SWATgrid) and MODFLOW was calibrated under steady state condition with its integrated recharge calculation scheme. This was followed by the linked SW-GW approach simulation, where, the lumped baseflow estimation was replaced by the detailed GW flow estimation by MODFLOW and the recharge calculation of MODFLOW was replaced by the comprehensive recharge estimation by the SWATgrid model. The findings show that for both study catchments the linked SW-GW modelling approach results in more realistic runoff simulation under hydroclimatic variability compared to the stand-alone SWATgrid model. The findings of this thesis emphasise the importance of the identification of mechanisms governing R-R non-stationarity at both annual and seasonal scales. Also, it is recommended that, for arid/semi-arid catchments that have experienced, or are projected to experience, non-stationarity in R-R relationships (e.g. during multi-year droughts), a linked SW-GW modelling approach, such as that presented here, be employed. Otherwise, runoff estimates will continue to be unrealistic, especially during droughts and especially given projections of a hotter and drier future for much of SEA. These findings have direct implications for current and future water resources management in Australia, and anywhere else which experiences, or is projected to experience, non-stationarity in R-R relationships. Furthermore, the insights gained also contribute to the aims of the International Association of Hydrological Sciences decade (2013-2022) Panta Rhei, which focusses on improving our capability to make predictions of water resources dynamics to support sustainable societal development in a changing environment.

This study aimed to determine whether rainfall regime has driven differentiation in the Australian perennial grass, Austrodanthonia caespitosa, resulting in local ecotypes possessing characters, such as deep rootedness or summer activity, that may be particularly useful in reducing deep drainage for salinity mitigation, or whether the species shows a plastic response in root growth to soil water distribution. Rainfall regime varies within a given annual rainfall because size and ditribution of rainfall event vary. This can have an important effect on soil water distribution, both spatially and temporally. This study investigates the relationship between rainfall regime and the structure of root systems in local populations of Austrodanthonia caespitosa (Gaudich.), Firstly, it examined a number of indices useful in quantifying variation in small-scale rainfall regime, including seasonal bias, event size, event frequency, and the clustering of events, as well as how rainfall event size may be changing over time across Australia. The variation in soil water distribution that results from different rainfall regimes is expected to interact with root distribution in plants, either acting as a selective force and driving genotypic differentiation in response to soil water availability, or through plasticity in root placement. The relationship between rainfall regime and root depth distribution was examined in Austrodanthonia caespitosa (Gaudich.), or white-top wallaby grass, a perennial grass common across southern Australia. Growth and reproductive traits of plants grown from seeds collected from across the range of this species under a single rainfall regime were compared and correlated with the rainfall indices and soil type in order to establish possible abiotic explanations for trait variability. Phenological characters were found to be particularly variable between ecotypes, but high local variation between ecotypes suggested factors operating on a spatial scale smaller than the rainfall gradients are responsible for population differentiation. In order to investigate the interaction between rainfall event size and root depth, an experiment was conducted to investigate plant response to watering pulse size and frequency, with plants grown under a range of controlled watering regimes, and root depth distribution compared. The primary response in root growth was plastic, with shallow roots being developed under small, frequent events, and deep roots developed under large, infrequent waterings. Differences between ecotypes were less important, and there was no interaction between ecotype and watering treatment, indicating the same degree of plasticity in all ecotypes. Plants from a range of populations were grown under a controlled climate, first under winter conditions, then under summer conditions, with summer water withheld from half the plants, in order to determine the response to summer watering and summer drought. Plants that were watered over summer showed a strong growth response, increasing shoot biomass significantly. This effect was particularly strong in South Australian populations, which was unexpected as they originate from a region with low, unpredictable summer rainfall. Root depth was not strongly influenced by summer watering treatment. Finally, an evolutionary algorithm model was constructed in order to examine optimal plant traits under a variety of rainfall regimes. The model highlighted the importance of the interaction between rainfall regime and soil type in determining optimal root placement. Variable root cost with depth was also found to be an important trade-off to be considered, with high root loss in the surface soil layers, due to high temperatures, making a shallow rooted strategy less efficient than if root costs were equal throughout the root system. Overall, no ecotypes of A.caespitosa could be identified that had characters particularly suited to deep drainage reduction, as the drought tolerant nature of the species, and the dormancy during times of drought, may lead to low overall water use. However, it may be a useful native component in pasture systems, due to its strong growth response to summer rainfall, a characteristic found to be particularly strong in a number of South Australian ecotypes.
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2008

This study aimed to determine whether rainfall regime has driven differentiation in the Australian perennial grass, Austrodanthonia caespitosa, resulting in local ecotypes possessing characters, such as deep rootedness or summer activity, that may be particularly useful in reducing deep drainage for salinity mitigation, or whether the species shows a plastic response in root growth to soil water distribution. Rainfall regime varies within a given annual rainfall because size and ditribution of rainfall event vary. This can have an important effect on soil water distribution, both spatially and temporally. This study investigates the relationship between rainfall regime and the structure of root systems in local populations of Austrodanthonia caespitosa (Gaudich.), Firstly, it examined a number of indices useful in quantifying variation in small-scale rainfall regime, including seasonal bias, event size, event frequency, and the clustering of events, as well as how rainfall event size may be changing over time across Australia. The variation in soil water distribution that results from different rainfall regimes is expected to interact with root distribution in plants, either acting as a selective force and driving genotypic differentiation in response to soil water availability, or through plasticity in root placement. The relationship between rainfall regime and root depth distribution was examined in Austrodanthonia caespitosa (Gaudich.), or white-top wallaby grass, a perennial grass common across southern Australia. Growth and reproductive traits of plants grown from seeds collected from across the range of this species under a single rainfall regime were compared and correlated with the rainfall indices and soil type in order to establish possible abiotic explanations for trait variability. Phenological characters were found to be particularly variable between ecotypes, but high local variation between ecotypes suggested factors operating on a spatial scale smaller than the rainfall gradients are responsible for population differentiation. In order to investigate the interaction between rainfall event size and root depth, an experiment was conducted to investigate plant response to watering pulse size and frequency, with plants grown under a range of controlled watering regimes, and root depth distribution compared. The primary response in root growth was plastic, with shallow roots being developed under small, frequent events, and deep roots developed under large, infrequent waterings. Differences between ecotypes were less important, and there was no interaction between ecotype and watering treatment, indicating the same degree of plasticity in all ecotypes. Plants from a range of populations were grown under a controlled climate, first under winter conditions, then under summer conditions, with summer water withheld from half the plants, in order to determine the response to summer watering and summer drought. Plants that were watered over summer showed a strong growth response, increasing shoot biomass significantly. This effect was particularly strong in South Australian populations, which was unexpected as they originate from a region with low, unpredictable summer rainfall. Root depth was not strongly influenced by summer watering treatment. Finally, an evolutionary algorithm model was constructed in order to examine optimal plant traits under a variety of rainfall regimes. The model highlighted the importance of the interaction between rainfall regime and soil type in determining optimal root placement. Variable root cost with depth was also found to be an important trade-off to be considered, with high root loss in the surface soil layers, due to high temperatures, making a shallow rooted strategy less efficient than if root costs were equal throughout the root system. Overall, no ecotypes of A.caespitosa could be identified that had characters particularly suited to deep drainage reduction, as the drought tolerant nature of the species, and the dormancy during times of drought, may lead to low overall water use. However, it may be a useful native component in pasture systems, due to its strong growth response to summer rainfall, a characteristic found to be particularly strong in a number of South Australian ecotypes.
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2008

Effective management of water resources, including surface and ground water, is vital and relies on a thorough understanding of climatic and hydrological (or 'hydroclimatic') variability. In Australia hydroclimatic variability is associated with several large-scale climate modes, including remote phenomena such as El Nino - Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD), and more regional climate indices such as the sub-tropical ridge (STR). Individually, the large-scale climate regimes typically associated with rainfall events are well understood. However, less is known about the interactions between, or combinations of, different large-scale conditions that influence Australian hydroclimatic regimes. These interactions are non-linear so traditional statistical frameworks may be unable to adequately characterise these relationships. Classification and Regression Trees (CART) are well suited to analysing relationships between predictor and response variables, including those based on categorical events, that may be modulated by several predictor variables acting together. By employing a more appropriate and novel statistical method this thesis aims to better understand relationships between large-scale modes of climate variability and Australian hydroclimatic regimes. In this work, tree-based models were used to classify regional Australian rainfall regimes from indices of ENSO, the IOD and the STR, yielding the following conclusions. (1) Interactions between tropical (ENSO, IOD) predictor variables and the STR control the strength of the tropical teleconnection and the influence on regional rainfall regimes in southern Australia. When tropical modes and the STR are in the same phase, rainfall regimes are continent-wide and spatially coherent. However, when indices of climate modes are in the opposite phases, i.e. El Nino combined with low STR intensity, the modulation of the tropical teleconnection by the STR is evident, as rainfall anomalies are confined to the northeast of the continent. (2) The influence of both STR intensity and position on rainfall regimes in southeastern Australia was defined. STR position was crucial for defining two distinct types of "wet" autumns, a "summer-like" ("winter-like") regime when the STR was in a southerly (northerly) position. The summer-like regime occurs at frequencies that have not changed detectably over the instrumental record. However, the frequency of the winter-like regime has declined significantly. In addition, the dry regime defined by high STR intensity has been the most frequent regime in recent years, consistent with the attribution of STR intensity as the main driver of the Millennium Drought. (3) The predictive persistence of relationships between a suite of predictor variables (indices of ENSO, IOD and the STR) and rainfall, upper-layer and lower-layer soil moisture was explored. The predictability of spring rainfall was similar using both random forests (a bootstrapping implementation of CART) and linear regression, suggesting results are not dependent on method. The key result, of possible use in seasonal forecasting, is that, deep soil moisture in spring and summer exhibits significantly more predictability than rainfall and shallow soil moisture, due to the persistence of tropical climate drivers and the removal of high-frequency variability in deep layers by natural temporal smoothing as soil moisture is transferred to deep soil layers.

The hidden state Markov (HSM) model is introduced as a new conceptual framework for modelling long-term persistence in hydrological time series. Unlike the stochastic models currently used, the conceptual basis of the HSM model can be related to the physical processes that influence long-term hydrological time series in the Australian climatic regime. A Bayesian approach was used for model calibration. This enabled rigourous evaluation of parameter uncertainty, which proved crucial for the interpretation of the results. Applying the single site HSM model to rainfall data from selected Australian capital cities provided some revealing insights. In eastern Australia, where there is a significant influence from the tropical Pacific weather systems, the results showed a weak wet and medium dry state persistence was likely to exist. In southern Australia the results were inconclusive. However, they suggested a weak wet and strong dry persistence structure may exist, possibly due to the infrequent incursion of tropical weather systems in southern Australia. This led to the postulate that the tropical weather systems are the primary cause of two-state long-term persistence. The single and multi-site HSM model results for the Warragamba catchment rainfall data supported this hypothesis. A strong two-state persistence structure was likely to exist in the rainfall regime of this important water supply catchment. In contrast, the single and multi-site results for the Williams River catchment rainfall data were inconsistent. This illustrates further work is required to understand the application of the HSM model. Comparisons with the lag-one autoregressive [AR(1)] model showed that it was not able to reproduce the same long-term persistence as the HSM model. However, with record lengths typical of real data the difference between the two approaches was not statistically significant. Nevertheless, it was concluded that the HSM model provides a conceptually richer framework than the AR(1) model.
PhD Doctorate

The hidden state Markov (HSM) model is introduced as a new conceptual framework for modelling long-term persistence in hydrological time series. Unlike the stochastic models currently used, the conceptual basis of the HSM model can be related to the physical processes that influence long-term hydrological time series in the Australian climatic regime. A Bayesian approach was used for model calibration. This enabled rigourous evaluation of parameter uncertainty, which proved crucial for the interpretation of the results. Applying the single site HSM model to rainfall data from selected Australian capital cities provided some revealing insights. In eastern Australia, where there is a significant influence from the tropical Pacific weather systems, the results showed a weak wet and medium dry state persistence was likely to exist. In southern Australia the results were inconclusive. However, they suggested a weak wet and strong dry persistence structure may exist, possibly due to the infrequent incursion of tropical weather systems in southern Australia. This led to the postulate that the tropical weather systems are the primary cause of two-state long-term persistence. The single and multi-site HSM model results for the Warragamba catchment rainfall data supported this hypothesis. A strong two-state persistence structure was likely to exist in the rainfall regime of this important water supply catchment. In contrast, the single and multi-site results for the Williams River catchment rainfall data were inconsistent. This illustrates further work is required to understand the application of the HSM model. Comparisons with the lag-one autoregressive [AR(1)] model showed that it was not able to reproduce the same long-term persistence as the HSM model. However, with record lengths typical of real data the difference between the two approaches was not statistically significant. Nevertheless, it was concluded that the HSM model provides a conceptually richer framework than the AR(1) model.
PhD Doctorate

Research Doctorate - Doctor of Philosophy (PhD)
The national seasonal forecasting system utilised by Australia’s Bureau of Meteorology is specifically focused on capturing El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) induced atmospheric and oceanic variability in the Indian and Pacific Ocean regions. Seasonal forecast skill is reasonable in some parts of the country but not in South Australia (SA). It is hypothesised that ENSO and IOD are not the major climate drivers of seasonal rainfall variability in SA which results in poor seasonal forecast skill in SA and that identification of the key climate drivers can help guide seasonal forecasting in this region. An investigation is therefore undertaken with the aim of identifying the key climate drivers of rainfall variability in SA. Initially, to determine the appropriate rainfall data to be used in the investigation, an in depth analysis of rainfall data quality is carried out which provides key insights into issues with gridded rainfall data products and provides recommendations for the use of gridded rainfall data in climate studies. A suite of climate drivers (and their associated indices) from the Indian, Pacific, Southern and North Atlantic Ocean regions are then identified and their relationships between seasonal rainfall recorded at various gauges in SA are assessed using a simple linear correlation analysis and nonlinear stratification approach. Relationships between individual climate drivers and rainfall are initially investigated but the importance of taking the combined impacts of climate drivers into account is also highlighted. The results of this analysis indeed confirm that ENSO and IOD are not the key drivers of seasonal rainfall variability in SA. The work is then extended by using a novel method for climate predictor selection to both identify the key combination of drivers that explain the most seasonal rainfall variability in different regions of SA and to determine the hierarchy of importance of the key drivers. The Subtropical Ridge (STR) is confirmed as the most important driver of rainfall variability in southern SA in autumn, winter and spring with SST variability in the Indian and Pacific Oceans acting as secondary drivers. The importance of the Southern Annular Mode in combination with the STR for spring rainfall in southern SA is also identified. In northern SA, rainfall variability is found to be dominated by a combination of Indian and Pacific Ocean SST variability but not specifically ENSO and IOD. It is found from this analysis that a maximum of 55% of rainfall variability can be explained by any of the selected climate driver combinations for any season and gauge in SA, which is an improvement on existing seasonal forecast skill in SA. Finally, the practical implications of the climate driver-rainfall relationships identified are investigated through the assessment of the variability of the SA’s cropping boundary, known as Goyder’s Line. It is found that the cropping boundary shifts according to different phases of large-scale climate drivers, in particular the STR intensity, such that when (for example) the STR is more intense than average, areas that are normally deemed as suitable for cropping have an increased chance of not receiving adequate growing season rainfall. This risk is found to be further enhanced when the STR is considered in combination with other drivers. Ultimately, the insights from this thesis and the future work proposed provide a key focus and direction for improving seasonal rainfall forecasting in SA.

Mawson Lakes is a new suburban housing development, situated 12 kms from the city of Adelaide in South Australia. The developers, the Mawson Lakes Joint Venture (MLJV), and the local council, the City of Salisbury, intend to capture all stormwater entering the site and recondition all wastewater. The water will then be supplied to residents and businesses for non-potable usage. Modelling the behaviour of the Mawson Lakes catchment under extreme conditions such as drought and prolonged periods of high rainfall will allow the project team to determine optimal water management strategies for the catchment. One of the problems facing the team is the prediction of future rainfall patterns and the typical form of extreme events. In this thesis I have used historical records to construct synthetic rainfall data that will allow the project team to investigate a wide range of typical behaviour. The Gamma distribution has been widely used to approximate the probability density function (PDF) of monthly rainfall totals. However, there is no natural way to extend this method directly to obtain a joint PDF for rainfall densities associated with two or more months, unless the monthly totals are independent. I propose a modified method to construct a suitable PDF using parameters from the maximum likelihood estimate for a marginal Gamma distribution and a series of associated Laguerre polynomials. This series of special functions allows us to match the correlation between monthly totals and to match the observed moments with any level of precision needed. The joint PDF for two months is constructed using a sum of products of associated Laguerre polynomials. In order to get an analytic expression for the marginal distributions and the associated cumulative probabilities, it is convenient to use a weighted total and a weighted proportion contributed from the first month. The method makes extensive use of well-known formulae from the theory of special functions. The cumulative marginal probability density for the weighted total and the cumulative conditional probability density for the weighted proportion are used to generate simulated rainfall totals for each month in a two month period. In theory the simulated data is statistically identical to the observed data. In practice we apply standard statistical methods to check that the simulated data is consistent with the observed data. This method can be extended to the general case of any number of months, but computationally is restricted to only three. For this reason an alternative method is proposed to generate synthetic data for more than three months, which uses groups and subgroups of months, but still retains the characteristics of the original PDF. Although the series method could also be used to model a sequence of days, I propose an alternative method using Markov processes. This method will match a sequence of daily totals, generated from a probability transition matrix, to the monthly total generated by the series method. This methodology allows the research team to simulate certain special cases such as droughts and prolonged periods of high rainfall. These unusual events are of great interest in catchment planning and management.
thesis (PhDMathematics)--University of South Australia, 2004.

Understanding anthropogenic changes in rainfall in Australia is difficult as Australia experiences one of the highest variable rainfall climates in the world. Firstly, this research aims to understand the observed historical changes in various characteristics of mean and extreme rainfall in Australia. Secondly, the research aims to understand the role of anthropogenic forcing and large-scale variability in driving changes in mean and extreme rainfall in Australia. Lastly, this research aims to identify the shortcomings of existing methods to study historical and future changes in rainfall and develop robust new approaches. 1. A comprehensive review of the persistent increase in rainfall in northwest Australia (NWA) since 1950, and a strong decrease in the southwest of Western Australia (SWWA) and southeast Australia (SEA), finds there are still significant knowledge gaps in our understanding of underlying mechanisms behind some of these changes. Extreme rainfall follows a similar trend to mean rainfall; however, very few regions show significant long-term historical changes in extreme rainfall. 2. Anthropogenic forcings play a significant role in modulating rainfall in NWA. Investigation using a set of CMIP5 models shows that the persistent increase in mean and extreme rainfall in NWA is better captured when aerosol forcings are incorporated. While aerosols lead to increased rainfall, greenhouse gases lead to a decrease in rainfall, resulting in an offsetting impact between aerosols and greenhouse gases. This study indicates the importance of correct representation of the interaction between natural drivers and all anthropogenic forcings (i.e. not just greenhouse gases) in climate models. 3. This research presented in this thesis indicates that the timing of extreme rainfall varies largely depending on the phases of ENSO and IPO and their interaction, particularly in SEA. Australia has a clear north and south distinction in the timing of extreme rainfall. Extreme rainfall in the north usually occurs in the summer, while in the south it typically occurs in late autumn/winter. The area of summer extreme rainfall extends southward (northward) during a negative phase of IPO (positive IPO). Variability in the timing of extreme rainfall is largest in SEA, indicating that extremes can occur at any time of the year in this region. During El Nino years, SEA receives extreme rainfall in late autumn/winter, and during La Nina years extremes usually occur in spring/summer months. Understanding these relationships have major implications on improving seasonal prediction of extremes. 4. The relationship between extreme rainfall and temperature, the scaling rate, has been used in previous studies to provide robust projections for extreme rainfall. However, there are large regional variations in scaling rates, with a rate higher than expected from the Clausius-Clapeyron (C-C) relationship found in the tropical north and south of Australia. Further decomposition into dynamic and thermodynamic drivers of extreme rainfall shows that dynamics play a key role in the high scaling rate in the north, while thermodynamic drivers of extreme rainfall play a crucial role in the south of Australia. Scaling rates in future simulations are higher than in historical simulations. This non-stationary nature of scaling rates makes it challenging to project extreme rainfall. 5. Lastly, a novel approach to detect long-term changes in rainfall characteristics is developed. By studying rainfall events (defined as consecutive n number of rain days), a continent-wide increase in the frequency and intensity of short duration (1-2 day) events is found and is evident across all seasons. In tropical north Australia (north of 20S), there is an increase in the frequency of long persistent (> 6 days) rainfall events, whereas the drought-prone regions in the south (below 20S) show a decrease in the frequency of rainfall events of duration > 2 days.

Copy of author's previously published work inserted.
Bibliography: leaves 261-306.
xxix, 308 leaves : ill. (some col.), maps ; 30 cm.
The objectives of the project were: i. to determine whether there are competitive interactions between Aporrectodea trapezoides and A. caliginosa and A. rosea.--ii. to investigate compeditive interactions between A. calignosa, Microscolex dubius and A. trapezoides.--iii . to determine the likely impact of A. longa on soil fauna, especially the native earthworm, Gemascolex lateralis, in native ecosystems.
Thesis (Ph.D.)--University of Adelaide, Dept. of Soil Science, 1996

Wheat (Triticum aestivum) production is important to global food security and the livelihoods of those who cultivate it. Increases in water-limited potential yield (PYw) and farm yield (FY) are necessary to keep pace with global demand, and in order for Australian growers to remain competitive in a changing climate and with declining terms of trade. In drought prone environments such as south-eastern Australia, alignment of the key developmental stage of flowering to the period that is optimal for the local climate is a critical determinant of yield. The optimal flowering period (OFP) begins when the risk of frost decreases, and ends to avoid increasing temperature, heat and water stress during grain fill. Flowering time is a function of the interaction between the speed of plant development (genetic, G), establishment date (management, M) and prevailing seasonal conditions (environment, E). Autumn rainfall decline, extreme spring weather and increasing farm size challenge traditional G x M combinations which are currently used to achieve the OFP in south-eastern Australia i.e. predominately fast developing spring wheats sown in late-April to early May. The objective of this study was to identify novel G x M combinations that stabilise flowering and maximise yield under changing rainfall patterns and recent changes to farming systems. This study used crop simulation and conducted field experiments in Temora, New South Wales (NSW); Berriwillock, Victoria; Minnipa, South Australia and Cunderdin, Western Australia. Firstly, OFPs were quantified in south-eastern Australia, the area most affected by autumn rainfall decline to align novel G x M strategies accordingly. Simulation demonstrated that the predicted timing and duration of OFPs varied with site and season. The relative importance of seasonal water supply and demand and extremes of temperature in defining the window also varied. To identify the physiological changes associated with breeding, the PYw and other parameters were quantified and compared at common sowing or flowering dates with a historic set of NSW cultivars released between 1901 and 2014. Genetic improvement through this period, increased grain yield at a rate of 26 kg ha-1 pa-1 regardless of sowing or flowering dates. The slow development and stable flowering observed in historic cultivars and superior partitioning to grain of modern cultivars were independent, and could potentially be combined in new cultivars to achieve future yield gains. Yield results for a novel fast-winter genotype (FW, with photoperiod insensitivity and requiring vernalisation) grown in a diverse set of environments, supported this hypothesis. The FW development pattern extended sowing windows while achieving 10-20% higher yields than current spring cultivars. The flowering stability index (1 minus the ratio of range in thermal time for flowering for each cultivar, to the range in thermal time of sowing dates) of the FW genotype was improved for the sowing dates currently used by farmers. Finally, novel agronomic packages to capture the higher yield potential of FW cultivars was investigated using simulation. Reliance on irregular rainfall to establish FW wheat could be reduced, and early establishment opportunities increased by sowing genotypes with long coleoptiles into stored sub-soil moisture accumulated during fallow. Combining the G x M flowering date stabilising factors; winter wheat, long coleoptile, early sowing and fallow reduced the reliance on autumn rainfall for timely crop establishment to provide a further buffer against seasonal climate variability. Consequently, simulated whole farm yield was increased as a greater area of wheat flowered during the optimal period. To achieve the productivity increases demonstrated here requires continued collaboration between agronomists and breeders. This includes the development of winter wheat cultivars with long coleoptiles that are adapted to different growing season lengths and OFPs, such that crops can be established earlier and emerge from a greater depth than current cultivars.

Drought is a global and recurrent natural phenomenon, the inevitable consequence of meteorological variability. This natural hazard brings about devastating effects because water is one of the most fundamental commodities for human survival, and a lack of water can result in varying consequences, from mere inconvenience to life threatening instances. Drought cannot be prevented but its effects can be mitigated through the design of appropriate water resource infrastructure and management strategies. The goal of this thesis is to model the spatial and temporal characteristics of drought occurrence in Australia, the driest continent. In doing so predictions can be made, levels of risk can be evaluated and conditional estimates of drought can be based on climatic state variables. For insight into the nature of drought in Australia, multivariate models of drought characteristics are developed. Preliminary analysis demonstrates high correlations between several drought characteristics, these are the drought severity, intensity and duration. This thesis applies the copula concept, which is a versatile means of modelling their dependence structure. Copulas are multivariate uniform distributions, which allow the joint behaviour of variables to be modelled independently from their marginal distributions. This research extends the application of copulas by investigating the effect of climate variability on copula models and subsequent drought characteristics. Two different copula families are fitted to the drought characteristics to demonstrate the importance of tail dependence when modelling extreme climatic events. An important application of these models is the calculation of return periods of extreme drought events exceeding certain thresholds, taking account of variability in climatic indices. A second objective is to forecast drought at various spatial resolutions. The most straightforward method are regression and ARMA models that incorporate global climatic indicators. The effect of climatic variation on Australia's precipitation is examined by investigating the association between climatic indices and the multivariate distribution of drought at numerous sites across Australia. Two classification strategies for forecasting rainfall are compared using significance testing based on multiple comparison techniques. Further to this, rainfall forecasting relationships are explored using global sea-surface temperature anomalies. The versatility of copula models is demonstrated through short-term rainfall predictions for neighbouring rainfall districts, using separate copulas conditioned on antecedent climate conditions. This technique is shown to improve rainfall predictions in neighbouring districts and improve estimates of drought probability.
Thesis (Ph.D.) -- University of Adelaide, School of Mathematical Sciences, 2010

The use of annual-based pasture and/or annual crops is now common practice in the higher rainfall regions of southern Australia where livestock grazing is the traditional practice. The lower water use of these annual-based systems, compared with systems based on perennial pastures, exacerbates issues of waterlogging, rising watertables and salinity in these regions. For environmental reasons farming systems used in the higher rainfall regions should target the use of more perennials in the landscape, but this should not be done at the expense of farm productivity or profitability. Intercropping, where the pasture component of the system is a perennial species, may provide the opportunity to maintain or improve farm productivity whilst delivering favourable environmental outcomes. A study of crop/perennial pasture intercrops is the core investigation undertaken in this thesis. Perennial pasture species lucerne (Medicago sativa) and chicory (Cichorium intybus) were established and maintained for three seasons with annually sown (2006-08 seasons) crop species (wheat (Triticum aestivum), lupin (Lupinus angustifolius) and canola (Brassica napus)), in a double skip row arrangement. These intercrops were compared for production, resource use and farm productivity with the individual crops and pastures grown as monocultures. Yields of grain crops were reduced when grown in intercrop with lucerne and chicory. Grain yield reductions ranged from 0-46% for wheat, 45-74% for lupins and 8-83% for canola. Pasture dry matter was also reduced when intercropped, ranging from 0-78% for lucerne and 19-78% for chicory. Despite the reduction in crop and pasture production, the Land Equivalent Ratio (LER) (used as a measure of the productivity of the intercropping system) ranged from 0.71-1.66, with all intercrop combinations over-yielding (LER 1.01 -1.66) in favourable growing seasons. With soil moisture becoming limited during September/October (measured using Time Domain Reflectometry), the grain yield components of wheat heads/m² , number of lupin branches/plant, pod number/plant and pasture dry matter were reduced by competition. Lucerne intercrops gave higher yield penalties to the companion species, attributed to greater competition for soil moisture between the component species. Higher soil moisture (9-25mm) for monoculture chicory, compared to monoculture lucerne, indicates chicory growing in intercrop was not likely to compete as strongly for water as lucerne. Plant height and Leaf Area Index (LAI) measurements were taken to assess light capture and showed minimal incidence of light competition in the intercrops. As a result, it was concluded that competition for water was the main resource competition responsible for yield reductions in intercrops. The Agricultural Production System Simulator (APSIM) model was used to try to assess longer-term intercrop productivity. The model was satisfactory in simulating monoculture crop production; however there was poor agreement for monoculture lucerne production and this subsequently affected the modelled agreement with intercrop production. Notwithstanding these discrepancies, some of the modelled data and extrapolated data were used to produce a medium-term productivity dataset for economic analysis. Economically, the intercrops were found to have higher gross margin returns than monoculture pastures, and lower gross margins of $39-55/ha when compared to monoculture crops. Despite yield reductions in the intercrop components, intercropping increased productivity compared to growing the components as monoculture stands. It also provided an environmental benefit of retaining perennial pastures in the system, and produced comparable economic returns to the growing of monocultures stands/swards.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2011

Masters Research - Master of Philosophy (MPhil)
Significant declines in the catch rates of smooth hammerhead sharks (Sphyrna zygaena) have recently been reported off the coast of New South Wales, Australia. Quantitative investigations on the life history and correlates of distribution of exploited marine species is fundamental in providing sound species management, as resulting quantifiable results can help determine how population structures are affected by fishing, and their capacity to recover from reduced stocks. This information is particularly important for commercially targeted animals, such as sharks. This thesis assesses the age, growth and distribution of juvenile smooth hammerhead sharks (Sphyrna zygaena) on the east coast of Australia. Vertebra, along with information on sample sex, size and stage of maturity were collected from 144 sharks. Lengths-at-age and growth rates were estimated from vertebral growth band counts for 82 females (109 – 284 cm total length (LT) and 62 males (120 – 255 cm LT). A multimodal approach (various growth functions) was used on pooled data and then separated by sex. These were compared using Akaike Information Criterion, sorted by Akaike score (Δ) with supporting evidence weighed using Akaike weights (ω). These indicate that a multimodal approach is necessary for growth analysis and that sex specific models are required. Females attained a maximum theoretical total length (L∞) of 302.2 cm and k of 0.06, whereas male L∞ was larger at 340.7 cm with a k of 0.06. Sex ratios were similar, however 96% of samples were not sexually mature, indicating that the coastal population of S. zygaena are mostly immature. These results have important implications in assessing the resilience of S. zygaena to stock depletion in south eastern Australian waters. This is fundamental for management decisions about status listings and allowable fishery interactions. Environmental variables influencing the catch of juvenile S. zygaena within the New South Wales Shark Meshing (Bather Protection) Program (SMP) were investigated to identify potential variables that explain spatial and temporal variability in catches. Using remotely sensed products and spatial conditions, 23 years of daily catch data from the SMP were applied to generalised linear mixed models with random effects to predict capture. The environmental variables assessed included sea surface temperature (SST), rainfall and chlorophyll a, as well as spatial and temporal variables such as distance to estuary mouth, substrate type, moon phase and southern oscillation index. Additionally, the introduction of acoustic deterrent devices were included in the model using year of introduction (1999). Corellative information indicates that juvenile S. zygaena catch were greatest at warmer SSTs, during dry weather, dark moon phases, in primarily sandy surroundings, and in nets closest to estuary mouths. Chlorophyll a concentration and southern oscillation did not help explain variation in catch. However, after adjusting for temporal changes in significant environmental factors, a temporal decline in catch was still present, indicating that the temporal decline in catch was not attributed to the environmental conditions assessed. The best predictor of temporal decline in the model was the introduction of acoustic deterent devices on nets. While a catch decrease after device introduction may be coincidental to an actual decline in the population, the close agreement between the fit of the model and the change point suggests that the temporal decline was associated with the introduction of the acoustic devices. This study suggests that further investigation at a finer level of detail (i.e. satellite tracking) is required into how each of the significant environmental conditions drives movement patterns of S. zygaena. This will also allow for a confirmation of the current studies method in detecting environmental patterns of occurrence and may allow an opportunity to test how acoustic alarms may affect their sensory biology. This thesis can assist decision makers in potential status listings both locally and worldwide. The identification of environmental and demographic catch patterns allow for informed coastal management decisions to take place, complementing future species specific adaptive management strategies.

Research Doctorate - Doctor of Philosophy (PhD)
The hydroclimate of eastern Australia is highly variable, with a multitude of large-scale climate processes bearing considerable influence on spatial and temporal rainfall characteristics. One phenomenon known for its contribution to rainfall and which operates on daily timescales, are East Coast Lows (ECLs). These intense low-pressure systems which take place over the subtropical east coasts of southern and northern hemisphere continents are typically associated with gale force winds, large seas, storm surges, heavy rainfall and flooding. While ECL impacts are usually seen as negative (e.g. flooding, storm damage etc.), the rainfall associated with ECLs is also very important for urban water security within the heavily populated eastern seaboard of Australia (ESA). This region of Australia contains a high number of city centres which are forecast to undergo disproportionate rates of growth compared to other areas in Australia. As a result, considerable pressure will be placed on water infrastructure and its resilience to climate variability. This thesis investigates the historical variability of ECLs, and their impact on eastern Australia’s hydroclimate, with particular emphasis placed on the ESA. Within the last decade, several comprehensive ECL databases have been developed. Despite this, inconsistencies remain as to what constitutes an ECL. This has hindered our ability to understand these systems and their impacts. In this thesis, we demonstrate that the definition of an ECL should include classification of the various ECL sub-types based on the synoptic-scale environments from which they form. ECL sub-types have different spatial distributions, seasonal cycles, and rainfall characteristics. Consequently, regions of eastern Australia and in particular the ESA, are influenced differently by different ECL sub-types. An investigation of rainfall across Australia and within the ESA suggests that the ESA is different to the rest of Australia and also not homogenous itself. For winter three separate divisions are identified: (i) the most northerly division from Moreton in Queensland (QLD) to the Manning region of New South Wales (NSW); (ii) the Hunter region south to the metropolitan Sydney area; and (iii) from Illawarra (NSW) to Eastern-central Victoria. For summer, autumn, and spring rainfall, two clear divisions are present: (i) the two most northerly divisions identified in winter combined and (ii) and the equivalent of the third and most southerly outlined for winter. The results suggest that the observed spatial inhomogeneity in rainfall across the ESA is at least in part due to ECLs and their sub-types. Though ECLs may only last a few days, they do have the capacity to provide considerable contributions to water storage reservoirs. Approximately one-third of ECL related rainfall occurs in the 48-hours prior to the system entering the Tasman Sea. Furthermore, given the trajectory of sub-types such as Inland Troughs (IT), Continental Lows (CL) and Southern Secondary Lows(SSL), much of this rainfall provides relief to western flowing headwaters, inland of the Great Dividing Range (GDR). An examination of seasonal rainfall contributions reveals that rainfall associated with Easterly Trough Low (ETL) is statistically significant along the central and northern latitudes of the ESA within winter. SSLs are also found to be significant for the southern extent of the ESA and extends its influence into spring, while CLs establish significance across Victoria. On daily time-scales ITs and ex-tropical cyclones are found to have significantly higher rainfall totals than non-ECL sources (and a number of other ECL sub-types) for their regions of preference. However, due to their infrequent nature, this did not translate into significant seasonal contributions, signifying an important difference in what sub-types present a risk to flooding and those, or rather their absence, that present a risk to water security. ECL sub-types and how their variability impact eastern Australia’s hydroclimate is also shown to be affected by large-scale climate processes. Changes in the spatial distribution of ECLs is found to reflect changes in the proportion of ECL sub-types. When in the La Niña phase, the El Niño Southern Oscillation (ENSO) (and its variant ENSO Modoki) tend to shift the spatial distribution of ECLs north. In winter, this also corresponds to an increase in overall ECL activity. This results in more than a 50% increase in ECL related winter rainfall, while similar magnitude of decrease was observed during the El Niño phase. Other mechanisms such as the Indian Ocean Dipole (IOD) were also found to have a considerable influence on the spatial distribution of ECLs and their associated rainfall. During negative IOD conditions, increases in rainfall west of the GDR corresponded to an increase in the proportion of westerly ECLs. Conversely, during positive IOD, ECL rainfall increases within the ESA owing to a change in the proportion of ECL sub-types. This thesis also provides insights into the importance of ECLs and their sub-types to a key streamflow monitoring station within the Hunter region of NSW. As an indicator for inflowpotential to the Grahamstown Dam, ECLs are responsible for 74% of all streamflow ≥ 99th percentile within the Williams River catchment. Likewise, the absence of ECLs is also shown to be associated with times where the Williams River is experiencing its lowest flow rates. The findings of this thesis are significant and demonstrate the influence ECL sub-types have on hydroclimatic variability in eastern Australia. It also reveals that existing climate related risks are different across the ESA and suggests that how those risks change into the future is also likely to be inconsistent across the ESA – and will likely depend heavily on what eventuates in terms of changes to ECL, and the various ECL sub-types and behaviour (e.g. frequency, timing, location, duration, magnitude and sequencing). This reinforces the need for locally relevant and practically useful climate science information and adaptation strategies - as opposed to State- or Countrywide information and adaptation approaches that are commonly used.