Rozprawy doktorskie na temat „Global runoff”

This thesis assesses long-term runoff projections from global multi-model ensembles used in hydrological impact studies. Firstly, the study investigates global-scale changes in frequency of high and low flow days towards the end of the current century, quantifying the relative contribution to uncertainty from global climate (GCMs) and global impact models (GIMs). Results show increases in high flows for northern latitudes and in low flows for several hotspots worldwide. Overall, GCMs provide the largest uncertainty; but GIMs are the greatest source of uncertainty in snow-dominated regions. Secondly, the ability of a set of GIMs to reproduce observed runoff is evaluated at the regional scale, indicating that GIMs capture well trends in low, medium, and high flows, but differ from observations with respect to medium and high flows timing. Thirdly, the contribution to uncertainty from GCMs, GIMs, Representative Concentration Pathways (RCPs), and internal variability is quantified for transient runoff until 2099. Over the USA, GCMs and GIMs are responsible for the largest uncertainty. Efforts to improve runoff projections should thus focus on GCMs and GIMs. In particular, GIMs should be evaluated in the region of study, so that models reproducing unrealistic runoff can be excluded, potentially yielding greater confidence in ensemble projections.

Includes bibliographical references (leaves 106-111).
The Breede River catchment in the South Western Cape is already under pressure for its water resources due to its supporting a variety of different land uses. The predominant land use in this catchment is agriculture, which demands the majority of river water for irrigation. The Department of Water Affairs and Forestry are currently investigating the future demand for water from the river, in this respect it is important to know what effect climate change will have on the change in river flow. Self Organising Maps (SOMs) are used to identify changes in the circulation systems contributing to the rainfall of the region and from this the potential change is assessed for the Breede River flow under future climate change. It is assessed that the runoff in the Breede River is expected to change under all the models of ECHAM4, CSIRO and HadAM. The magnitude of this alteration is calculated by using the change in the SOM node frequencies between the present and the future data. This is then subtracted from the present runoff data supplied by DWAF. A source of runoff decrease in the future is agricultural irrigation. The increase in irrigation under climate change is determined by inserting future climate data into an agricultural model. Once the increased amount of water used in irrigation is determined, it is subtracted from the projected future runoff. From this it is determined whether the river will be ecologically sustainable under climate change.

The purpose of this study was to use the Global Water Stormwater Sampler SS201 to characterize the urban runoff in Pecan Creek. Location of the samplers was influenced by land use and ease of installation. Determination of the constituents for analysis was modeled after those used in the NPDES permit for seven cities within the Dallas/Ft.Worth metroplex. Some metals, notably cadmium and arsenic, exceeded the U.S. EPA's MCL's. Statistical analysis revealed first flush samples to be significantly more concentrated than composite samples. Minimum discharge loadings were found to be significantly lower than maximum discharge loadings. Additionally there were significant differences of specific constituents between station locations and storm events.

L'innalzamento del livello del mare è una delle principali conseguenze del riscaldamento globale dovuto all'emissione di gas serra in atmosfera ed è quindi di cruciale interesse nello studio dei cambiamenti climatici. L'obiettivo di questa tesi di Dottorato consiste nell'analisi dell'importanza relativa dei vari processi che contribuiscono al cambiamento del livello del mare durante l'ultima decade del 20° secolo e il primo decennio del 21° secolo, mediante l'utilizzo di un modello numerico globale di circolazione oceanica ad alta risoluzione (1/4°). Lo studio è stato in seguito esteso nel futuro, fornendo proiezioni del cambiamento del livello del mare nei prossimo 20 anni e concentrando la nostra analisi sulla regione delle Piccole Isole del Pacifico, che rappresenta una delle aree più vulnerabili agli impatti legati all'innalzamento del livello del mare. Inoltre, la risposta dell'oceano a stime realistiche di scioglimento dei ghiacciai continentali di Antartide e Groenlandia, ricostruite a partire da dati gravimetrici e di modelli atmosferici, è stato investigato, essendo questa una delle principali cause del cambiamento del livello del mare.
As a major effect of anthropogenic greenhouse gases induced global warming, sea level rise is a key climate issue of crucial interest in the frame of climate change investigation. The aim of this Ph.D. thesis is to study the relative importance of the different processes that contribute to sea level change during the last decade of the 20th century and the first decade of the 21st century, by using an eddy-permitting Ocean General Circulation Model at a spatial resolution of 1/4°. We have further extended our analysis in the future, by providing projections of sea level change for the next 20 years at an unprecedented resolution of 0.25°, with particular focus on the Pacific Small Island region, which represents a highly vulnerable region to the impacts of sea level rise. The exchange of water between the ocean and Greenland and Antarctica ice-sheets is one of the major causes of sea level change. For this reason, the response of the ocean to a realistic ice-sheets runoff, reconstructed through a combination of gravimetric and atmospheric model data, has been investigated.

Water is essential for all life on earth. Global population increase and climate change are projected to increase the water stress, which already today is very high in many areas of the world. The differences between the largest and smallest global runoff estimates exceed the highest continental runoff estimates. These differences, which are caused by different modelling and measurement techniques together with large natural variabilities need to be further addressed. This thesis focuses on global water balance models that calculate global runoff, evaporation and water storage from precipitation and other climate data.

A new global water balance model, WASMOD-M was developed. Already when tuned against the volume error it reasonable produced within-year runoff patterns, but the volume error was not enough to confine the model parameter space. The parameter space and the simulated hydrograph could be better confined with, e.g., the Nash criterion. Calibration against snow-cover data confined the snow parameters better, although some equifinality still persisted. Thus, even the simple WASMOD-M showed signs of being overparameterised.

A simple regionalisation procedure that only utilised proximity contributed to calculate a global runoff estimate in line with earlier estimations. The need for better specifications of global runoff estimates was highlighted.

Global modellers depend on global data-sets that can have low quality in many areas. Major sources of uncertainty are precipitation and river regulation. A new routing method that utilises high-resolution flow network information in low-resolution calculations was developed and shown to perform well over all spatial scales, while the standard linear reservoir routing decreased in performance with decreasing resolution. This algorithm, called aggregated time-delay-histogram routing, is intended for inclusion in WASMOD-M.

Climate change poses significant threats to mountain ecosystems in North America (Barnett et al., 2005) and will subsequently impact water supply for human and ecosystem use. To assess these threats, we must have an understanding of the local variability in hydrometeorological conditions over the mountains. This thesis describes the continued development and application of a fine scale spatial hydrometeorological model, GENESYS (GENerate Earth SYstems Science input). The GENESYS model successfully simulated daily snowpack values for a 10 year trial period and annual runoff volumes for a thirty year period. Based on the results of these simulations the model was applied to estimate potential changes in snowpack over the St. Mary River watershed, Montana. GCM derived future climate scenarios were applied, representing a range of emissions controls and applied to perturb the 1961-90 climate record using the “delta” downscaling technique. The effects of these changes in climate were assessed for thirty year time slices centered on 2020s, 2050s, and 2080s. The GENESYS simulations of future climate showed that mountain snowpack was highly vulnerable to changes in temperature and to a lesser degree precipitation. A seasonal shift to an earlier onset of spring melt and an increase in the ratio of rain to snow occurred under all climate change scenarios. Results of mean and maximum snowpack were more variable and appeared to be highly dependent on scenario selection. The results demonstrated that although annual volume of available water from snowpack may increase, the seasonal distribution of available water may be significantly altered.
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A modelling approach focused on snow hydrology was developed and applied to project future changes in spring streamflow volumes in the St. Mary River headwaters basin, Montana. A spatially distributed, physically-based, hydrometeorological and snow mass balance model was refined and used to produce snow water equivalent (SWE) and rainfall surfaces for the study watershed. Snowmelt runoff (SR) and effective rainfall runoff (RR) volumes were compiled for the 1961-2004 historical period. A statistical regression model was developed linking spring streamflow volume (QS) at Babb, Montana to the SR and RR modelled data. The modelling results indicated that SR explained 70% of the variability in QS while RR explained another 9%. The model was applied to climate change scenarios representing the expected range of future change to produce annual QS for the period 2010-2099. Compared to the base period (1961-1990), average QS change ranged from -3% to -12% for the 2020s period. Percent changes increased to between -25% and -32% for the 2050s, and -38% and -55% for the 2080s. Decreases in QS also accompanied substantial advances in the onset of spring snowmelt. Whereas the spring pulse onset on average occurred on April 8 for the base period, it occurred 36 to 50 days earlier during the 2080s. The findings suggest that increasing precipitation will not compensate for the effects of increasing temperature in watershed SWE and associated spring runoff generation. There are implications for stakeholder interests related to ecosystems, the irrigation industry, and recreation.
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Nel mio lavoro di tesi è stata valutata l'influenza climatica sulle prestazioni dei tetti verdi relativamente alla riduzione del runoff, il risparmio energetico e il miglioramento della qualità dell'aria.

L'objectif de ce travail est une conlribution à l'analyse des processus de formation des crues sur un bassin méditerranéen à l'occasion des épisodes pluvieux. Nous avons essayé de comprendre les caractéristiques hydrologiques d'un bassin par une démarche mécaniste. Pour cela, nous avons étudié la part, dans le débit de la rivière pendant les crues, du débit provenant d'un écou!ement soit par ruissellement généralisé, soit souterrain ou de subsurface, soit sur zones saturées contributives. Le bassin versant a été schématisé comme la succession de deux unités hydrologiques: le versant et le réseau hydrographique. Ainsi, la première partie de ce mémoire est consacrée à l'analyse mécaniste des apports à la riuvière à l'échelle du versant. Pour chaque processus, une étude expérimentale a été menée afin d'étudier les lois qui régissent ces écoulement. Nous avons montré. que les écoulements en surface ne suivent pas une loi d'écoulement plan turbulent Les écoulements en litière, immédiatement sous la surface du sol, suivent une loi de Manning. Enfin, les écoulements de subsurface suivent une lol de Darcy. A l'échelle du versant, la modélisation des écoulements avec les lois mesurées ne les entretient jamais assez longtemps pour expliquer les hydrogrammes de bassin. La seconde partie de ce mémoire consiste en une modélisation à l'échelle du bassin des écoulements dans le cas des trois processus de formation des crues. Cette modélisation a cherché à reproduire les hydrogrammes du bassin. On montre que lorsque le bassin est sec, les écoulements proviennent principalement du ruissellement généralisé. Lorsque le bassin est plus humide, les pluies mettent d'abord en activité des écoulements souterrains et de subsurface, puis si les pluies sont importantes, le mécanisme d'écoulement sur surfaces saturées contributives devient prépondérant

Thesis (M.S.)--University of Wisconsin--Madison, 2004.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 40-45).

Uncertainty surrounds the understanding of natural variability in hydrologic extremes such as droughts and floods and how these events are projected to change in the future. This thesis leverages Global Climate Model (GCM) data to analyse 738 year streamflow scenarios in the Nelson-Churchill River Basin. Streamflow scenarios include a 500 year stationary period and future projections forced by two forcing scenarios. Fifty three GCM simulations are evaluated for performance in reproducing observed runoff characteristics. Runoff from a subset of nine simulations is routed to generate naturalized streamflow scenarios. Quantile mapping is then applied to reduce volume bias while maintaining the GCM’s sequencing of events. Results show evidence of future increases in mean annual streamflow and evidence that mean monthly streamflow variability has decreased from stationary conditions and is projected to decrease further into the future. There is less evidence of systematic change in droughts and floods.
May 2016

In order to study the impact of global runoff, sensitivity experiment (NoRiv) was carried out by shutting down the entire runoff into the ocean for a period of 200 years. The changes in NoRiv, compared to the reference simulation (CR), shows the impact of global runoff (NoRiv minus CR). The evolution of mean ocean SSS in the major ocean basins show that the upper– ocean reached a quasi-stabilized stage in the first 100 years in the NoRiv. Globally, when there is no runoff, the surface ocean turns saltier with the largest increase occurring off the mouths of major river systems. High salinity patches of more than 2 psu are found near the mouths of Amazon, Congo, Ganga–Brahmaputra, Yangtze, etc. The upper–ocean currents distribute the positive salinity anomalies generated near the river mouth of NoRiv to far away regions and open ocean. In accordance with our results using CCSM3.0 model, CESM1.0 also shows that the impact of runoff into the ocean on SSS is significantly higher in the extratropical ocean than in the tropics, though the tropical runoff is considerably higher (Vinayachandran, Jahfer, and Nanjundiah, 2015). Arctic Ocean recorded the highest rise in salinity as the ratio of runoff to the surface area of the basin is highest. The open ocean regions of Pacific exhibited the least change in salinity due to the vastness of the basin. We further analyzed the significance of this rise in SSS on the upper–ocean temperature, air–sea interaction, and rainfall. A saltier ocean in the NoRiv deepens the mixed layer of the upper–ocean owing to the increase in surface density. Though the mean MLD in the NoRiv is found to be deeper than the CR, the SST response to this change in ML is complex. In the simulation without runoff, the northern hemisphere oceans recorded a comparatively higher rise in surface temperature, mostly in the Atlantic Ocean. The change in SST in the NoRiv is primarily due to the weakening of upper–ocean stratification or due to changes in air–sea interaction in the coupled system. The equatorial Ocean of the Pacific Ocean recorded a mean cooling (of 0.2oC). But, the magnitude of the impact is relatively weaker in CESM1.0 as compared to CCSM3.0. The evolution of SST anomaly in the equatorial Pacific is a consequence of complex air–sea interaction. The appearance of cooler SST anomalies in the eastern equatorial Pacific of NoRiv generates a zonal pressure gradient resulting in an enhancement in easterlies. This, in turn, enhances wind– driven upwelling in the eastern equatorial Pacific leading to the formation of a La Niña–like SST anomaly in the equatorial Pacific. This La Niña–like SST anomaly in the equatorial Pacific has the potential to alter the Indian summer monsoon, one of the most dominant and regular features in the present–day tropical climate. It is well established that the cooler phase of equatorial Pacific, the La Niña, favors a higher rainfall over the Indian subcontinent. Existing theories on the teleconnection between the Indian monsoon and ENSO states that the summer– time changes in the equatorial Pacific SST results in convective anomalies in the Pacific Ocean that can impact the rainfall over the Indian subcontinent (Shaman and Tziperman, 2007). Chapter 6. Summary and Conclusions 151 A cooler Pacific, La Niña phase, favors negative convection anomalies in the tropical Pacific which leads to atmospheric convergence over Indian landmass and thereby affects the westward propagating jet termed as the North African–Asian jet (NAA; Shaman and Tziperman, 2007). The resultant negative vorticity anomalies over the Asian landmass during a La Niña phase lead to overall warming over the region that reinforces the meridional temperature gradient between equatorial Indian Ocean and landmass over Asia (Shaman and Tziperman, 2007). However, we find that the response of SSS, SST, and rainfall to the global runoff in the recent version (CESM1.0) is weaker than the earlier one (CCSM3.0). A higher ocean–land temperature gradient in the NoRiv is found to be favorable for increased intraseasonal activity over the Indian region leading to a stronger summer monsoon (Jiang, Li, andWang, 2004). Thus the improved monsoon in the absence of global runoff is thus a result of cooling in the equatorial Pacific and an upper–level vorticity guided strengthening of the meridional temperature gradient. The 0AMZ experiment is similar to the global runoff experiment (NoRiv) except that the runoff into the ocean from the Amazon river is shut down. The last 100 years of the model simulation shows that the Amazon runoff is a vital component of the large–scale, low–frequency oscillations in the Atlantic Ocean. When there is no input from the Amazon river, saltier water from the river mouth disseminates over the North Atlantic Ocean as far as the deepwater formation sites in the extratropics. Consequently, the upper–ocean mixed layer over the deep–convection zones in the Labrador and GIN Sea region deepen. AdeeperMLimplies strengthening of deepwater formation rate and a reinforced Atlantic meridional overturning circulation (AMOC). On a longer timescale, the atmospheric response to Amazon runoff is found to be consistent with the well established global impacts during a positive phase of AMOC. Chapter 6. Summary and Conclusions 152 A stronger AMOC brings cooler subsurface water to the surface in the southern tropical Atlantic Ocean by enhancing the upwelling rate. This cooler upper–ocean water is carried to the north of the equator by the cross–equatorial currents. Consequently, the upwelling branch of Hadley Cell in the equatorial Atlantic Ocean becomes weaker. This weakening of Hadley Cell has a negative feedback on the atmospheric meridional cells in the subtropics and extratropics. The North Atlantic Oscillation, the strength of which depends on the strength of winter–time (DJF) meridional circulation in the extratropical Atlantic Ocean, thus shifts to its negative phase. Though the impact of Amazon runoff on rainfall during winter is relatively weaker in the tropics, the landmass adjacent to the extratropical Atlantic Ocean shows significant responses. We found that the runoff–induced changes in surface temperature, winds, and rainfall over the United States and Europe are similar to the anomalies during a negative phase of NAO. The winter storms over northern Europe turn weaker along with a reduction in local rainfall. However, southern Europe and eastern Canada received higher rainfall in the absence of Amazon runoff, whereas the rainfall over the eastern US decreased. In the tropical Atlantic Ocean sector, the summer–time rainfall (JJA) response exhibits a see–saw pattern with a higher rainfall over the northern half and lower rainfall to the south. This spatial pattern of rainfall anomaly is a typical feature of feedback during a positive phase of AMOC. During a stronger AMOC, the warm surface waters of the southern tropical Atlantic is pushed to the northern tropics, and the cooler waters dominate over the south and along the equator. The SST anomalies thus formed is strikingly similar to the surface ocean signature during a positive Atlantic Multidecadal Variability (AMV), which is believed to be a subset of AMOC. The changes in rainfall in the 0AMZ is closely tied to the spatial pattern of SST anomaly such that a warmer northern equatorial Atlantic Ocean favors a higher rainfall over the region and vice versa. Thus when there is no input from the Amazon river, the AMOC and AMV shifts to a positive phase and thereby affect the surface temperature and rainfall over the tropical Atlantic Ocean during boreal summer.

Ocean acidification and thermal stress due to anthropogenic greenhouse gas emissions present significant, potentially interacting, threats to the future of coral reefs. Coastal reef environments, as in the case of the Great Barrier Reef (GBR), can also be exposed to terrestrial stressors. This thesis evaluates the combined effects of ocean acidification, rising temperatures and river inputs on the calcification of Porites corals along a transect across-shelf the central GBR, north of Townsville. Calcification rates were obtained for 41 long-lived Porites corals from 7 reefs, in an inshore to offshore transect across the central GBR. The boron isotope composition (d11B) of selected cores was used to reconstruct annual and sub-annual changes in seawater pH in inner-shelf and mid-shelf environments. These unique seawater pH records are integrated with sea-surface temperature, river discharge and rainfall records to assess the nature and cause of seasonal, interannual, decadal and long-term (̃50 years) trends in coral calcification. Significant across-shelf differences in the temporal variability and long-term evolution of coral calcification are documented and can be related to local and global-scale changes in environmental conditions and water quality. Corals in the mid-shelf and outer-reef regions of the GBR exhibit an increase in calcification of 10.9% (1.1% S.E.) and 11.1% (3.9% S.E.) respectively since ̃1950 which are associated to the rise in sea-surface temperatures. However, calcification rates of mid-shelf corals show a decline of 3.3% (0.9% S.E.) over the recent period (1990-2008). This may indicate that a thermal optimum for calcification has been reached. Calcification rates in inner-shelf reefs over 1930-2008 display a long term trend of decreasing calcification of 4.6% (1.3% S.E.). The interannual-decadal component of variation is modulated by wet and dry periods, particularly during the last ̃40 years. The negative effects of bleaching on coral growth are evident in inshore reefs, and are particularly strong during 1998, with a significant recovery occurring after 3 years. This translate to constant calcification rates of 1.1% (2.0% S.E.) for the inner-shelf reefs over 1990-2008. These results highlight the need to consider regional differences in environmental factors when assessing and predicting changes in the GBR. Sub-annual and annual variation in the d11B of inner-shelf corals record seasonal and interannual seawater pH changes of up to 0.5 pH units. This variability is overlain on a long-term decrease of 0.02 pH units per decade, consistent with estimates of surface seawater acidification due to rising atmosphere CO2 levels. Sub-annual low pH values occur in summer and partly reflect the effects of higher temperatures and increased calcification (a source of CO2). Higher d11B (pH) values are observed in wet years when nutrients supplied by river run-off promote extensive phytoplankton blooms that take up CO2 and increase seawater pH. Decreased calcification of inner-shelf corals during large flood events, despite higher pH conditions, may reflect increased shading, turbidity, sedimentation and/or competition for carbon. The complex interactions between processes that can affect coral calcification, particularly in coastal zones, need to be considered when predicting the future of coral reefs in warmer and more acidic oceans.

River discharge can affect ocean surface temperature by altering stratification within the oceanic mixed layer. A hitherto unexplored aspect of present climate is the feedback of river runoff onto climate. This thesis presents an investigation of the impact of global river runoff on oceans and climate using a fully coupled global climate model, Community Climate System Model (CCSM). Two model simulations for a period of 100 years have been carried out: 1) a reference run (CTRL) that incorporates all the features of a global coupled model with river runoff into the ocean embedded in it, and 2) a sensitivity run (NoRiv) in which the global river runoff into the ocean is blocked. Comparison of model climate devoid of fluvial discharge with the reference run reveals the significance of fluvial discharge in the present climate. By the end of 50 years of NoRiv experiment, salinity growth slows down and reaches a quasi-stable state. Regions close to river mouths exhibited maximum salinity rise that can potentially alter local density and stratification. On an average, denser and saltier waters in the NoRiv run annihilate barrier layer and form a deeper mixed layer, compared to CTRL run. Density gradient created by the modulation in salinity set forth anomalous currents and circulation across coastlines that carries coastal anomalies to open ocean, preventing local salinity buildup. Arctic Ocean, Bay of Bengal, northern high latitude Pacific and the Atlantic are the most affected regions in terms of changes in salinity and temperature. Model simulations demonstrate that major transformation in Arctic freshwater budget can have potential impact on northern Pacific and Atlantic climate. In the absence of runoff, global average sea surface temperature (SST) rise by about ~ 0.5oC, with major contribution from northern higher latitude oceans. In the Pacific, high latitude warming is related to deepening of mixed layer as well as the northward transport of low latitude warmer waters. Substantial cooling in the central equatorial Pacific (~1oC during winter) can alter large-scale ocean-atmosphere circulation, including El Niño-Southern Oscillation (ENSO). The reinforcement of Pacific and Atlantic western boundary currents aids the transport of warm saline water from low latitudes to higher latitudes. The results suggest that the river runoff can have potential impact on oceanic climate. Response of Indian summer monsoon rainfall to global continental runoff is also examined. In the NoRiv run, average summer monsoon rainfall over India increased by ~ 0.55 mm day−1. Consistent with the increase in annual average Indian monsoon rainfall, all other northern hemispheric monsoon systems showed an increase, while southern hemispheric monsoons weakened. Associated with enhanced monsoon, the periodicity of ENSO in the NoRiv run changes as a result of cooling tendency in the equatorial Pacific, a sign of consistent La Niña. Equatorial Pacific cooling, in spite of a global ocean warming trend, is found to be primarily because of the enhanced local easterly winds and resultant strong equatorial upwelling. Cold anomaly due to upwelling spread entire equatorial Pacific basin within a span of 50 years. The La Niña situation in the Pacific favored increased monsoon rainfall over Indian subcontinent. Another surprising result of this study is the strengthening of ENSO-monsoon relationship in the NoRiv run. This suggests that the river discharge can be considered as a dampening force in the ENSO-monsoon relationship. Northern hemisphere showed a clear warming in the NoRiv simulation compared to CTRL, the result of which is an enhanced trans-hemispheric gradient. Cross-equatorial winds triggered by this gradient blow from southern hemisphere and shift the Inter Tropical Convergence Zone (ITCZ) northward, increasing the precipitation in the northern hemisphere. The cooling in the eastern equatorial Indian Ocean and the warming in the west, reflected in the increase in number of positive Indian Ocean Dipole (IOD) events (9 positive and 5 negative IOD events in the last 50 years), also favored summer-time rainfall over India.

River discharge can affect ocean surface temperature by altering stratification within the oceanic mixed layer. A hitherto unexplored aspect of present climate is the feedback of river runoff onto climate. This thesis presents an investigation of the impact of global river runoff on oceans and climate using a fully coupled global climate model, Community Climate System Model (CCSM). Two model simulations for a period of 100 years have been carried out: 1) a reference run (CTRL) that incorporates all the features of a global coupled model with river runoff into the ocean embedded in it, and 2) a sensitivity run (NoRiv) in which the global river runoff into the ocean is blocked. Comparison of model climate devoid of fluvial discharge with the reference run reveals the significance of fluvial discharge in the present climate. By the end of 50 years of NoRiv experiment, salinity growth slows down and reaches a quasi-stable state. Regions close to river mouths exhibited maximum salinity rise that can potentially alter local density and stratification. On an average, denser and saltier waters in the NoRiv run annihilate barrier layer and form a deeper mixed layer, compared to CTRL run. Density gradient created by the modulation in salinity set forth anomalous currents and circulation across coastlines that carries coastal anomalies to open ocean, preventing local salinity buildup. Arctic Ocean, Bay of Bengal, northern high latitude Pacific and the Atlantic are the most affected regions in terms of changes in salinity and temperature. Model simulations demonstrate that major transformation in Arctic freshwater budget can have potential impact on northern Pacific and Atlantic climate. In the absence of runoff, global average sea surface temperature (SST) rise by about ~ 0.5oC, with major contribution from northern higher latitude oceans. In the Pacific, high latitude warming is related to deepening of mixed layer as well as the northward transport of low latitude warmer waters. Substantial cooling in the central equatorial Pacific (~1oC during winter) can alter large-scale ocean-atmosphere circulation, including El Niño-Southern Oscillation (ENSO). The reinforcement of Pacific and Atlantic western boundary currents aids the transport of warm saline water from low latitudes to higher latitudes. The results suggest that the river runoff can have potential impact on oceanic climate. Response of Indian summer monsoon rainfall to global continental runoff is also examined. In the NoRiv run, average summer monsoon rainfall over India increased by ~ 0.55 mm day−1. Consistent with the increase in annual average Indian monsoon rainfall, all other northern hemispheric monsoon systems showed an increase, while southern hemispheric monsoons weakened. Associated with enhanced monsoon, the periodicity of ENSO in the NoRiv run changes as a result of cooling tendency in the equatorial Pacific, a sign of consistent La Niña. Equatorial Pacific cooling, in spite of a global ocean warming trend, is found to be primarily because of the enhanced local easterly winds and resultant strong equatorial upwelling. Cold anomaly due to upwelling spread entire equatorial Pacific basin within a span of 50 years. The La Niña situation in the Pacific favored increased monsoon rainfall over Indian subcontinent. Another surprising result of this study is the strengthening of ENSO-monsoon relationship in the NoRiv run. This suggests that the river discharge can be considered as a dampening force in the ENSO-monsoon relationship. Northern hemisphere showed a clear warming in the NoRiv simulation compared to CTRL, the result of which is an enhanced trans-hemispheric gradient. Cross-equatorial winds triggered by this gradient blow from southern hemisphere and shift the Inter Tropical Convergence Zone (ITCZ) northward, increasing the precipitation in the northern hemisphere. The cooling in the eastern equatorial Indian Ocean and the warming in the west, reflected in the increase in number of positive Indian Ocean Dipole (IOD) events (9 positive and 5 negative IOD events in the last 50 years), also favored summer-time rainfall over India.

Throughout many of the world’s mountain ranges snowpack accumulates during the winter and into the spring, providing a natural reservoir for water. As this reservoir melts, it fills streams and recharges groundwater for over 1 billion people globally. Despite its importance to water resources, our understanding of the storage capacity of mountain snowpack is incomplete. This partial knowledge limits our abilities to assess the impact that projected climate conditions will have on mountain snowpack and water resources. While understanding the effect of projected climate on mountain snowpack is a global question, it can be best understood at the basin scale. It is at this level that decision makers and water resource managers base their decisions and require a clarified understanding of basin's mountain snowpack. The McKenzie River Basin located in the central-western Cascades of Oregon exhibits characteristics typical of many mountain river systems globally and in the Pacific Northwestern United States. Here snowmelt provides critical water supply for hydropower, agriculture, ecosystems, recreation, and municipalities. While there is a surplus of water in winter, the summer months see flows reach a minimum and the same groups have to compete for a limited supply. Throughout the Pacific Northwestern United States, current analyses and those of projected future climate change impacts show rising temperatures, diminished snowpacks, and declining summertime streamflow. The impacts of climate change on water resources presents new challenges and requires fresh approaches to understanding problems that are only beginning to be recognized. Climate change also presents challenges to decision makers who need new kinds of climate and water information, and will need the scientific research community to help provide improved means of knowledge transfer. This dissertation quantified the basin-wide distribution of snowpack across multiple decades in present and in projected climate conditions, describing a 56% decrease in mountain snowpack with regional projected temperature increases. These results were used to develop a probabilistic understanding of snowpack in projected climates. This section described a significant shift in statistical relations of snowpack. One that would be statistically likely to accumulate every 3 out of 4 years would accumulate in 1 out of 20 years. Finally this research identifies methods to improved knowledge transfer from the research community to water resource professionals. Implementation of these recommendations would enable a more effective means of dissemination to stakeholders and policy makers. While this research focused only on the McKenzie River Basin, it has regional applications. Processes affecting snowpack in the McKenzie River Basin are similar to those in many other maritime, forested Pacific Northwest watersheds. The framework of this research could also be applied to regions outside of the Pacific Northwestern United States to gain a similar level of understanding of climate impacts on mountain snowpack.
Graduation date: 2012