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1
HELLIES, MATTEO. "Extreme rainfall regime characterization in Sardinia using daily rainfall data". Doctoral thesis, Università degli Studi di Cagliari, 2016. http://hdl.handle.net/11584/266863.
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For the design of hydraulic structures for flood conveyance and discharge, or
protection of territory against flood is fundamental the knowledge of the ``extreme
rainfall regime'' in the area where the hydraulic structures must be set up.
Indeed the design flood is commonly evaluated as output of rainfall-runoff models that
receive as input the quantitative description of a rainfall extreme event with a given
exceedance probability.
This dissertation assesses the performance of different statistical approaches in
characterizing extreme rainfall in the island of Sardinia (Italy).
After a detailed review of the theoretical bases of existing methodologies, we compare
the results obtained from the use of:
a) a Generalized Extreme value (GEV) distribution model, and a Two component
Extreme Value (TCEV) distribution model, both applied to yearly maxima of daily
rainfall, and b) a Generalized Pareto (GP) distribution model applied to rainfall
excesses above a properly specified threshold. For the latter purpose, we use the
Multiple Threshold Method (MTM) developed by Deidda(2010), which demonstrate
good performance also in the case of quantized records.
In order to describe the spatial variation of TCEV, GEV and GP model parameters a
regional approach based on homogeneous regions, and two versions of Kriging (a
commonly used geostatistical approach) i.e. ordinary Kriging (OK), and Kriging for
uncertain Data (KUD), are compared.
The obtained results are very promising, pointing towards the use of: a)a GEV
distribution model for yearly rainfall maxima, and a KUD model to describe the spatial
variation of model parameters, and b)a GP model for rainfall excesses and either an OK
or a KUD model for the spatial variation of model parameters. The reason why the OK
and KUD approaches lead to the same results in the GP case, is attributed to the
robustness of the MTM method.
2
Welles, Edwin. "Comparison of rainfall sampling schemes using a calibrated Stochastic Rainfall Generator". Thesis, The University of Arizona, 1994. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu_etd_hy0062_m_sip1_w.pdf&type=application/pdf.
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Cramer, Sam. "New genetic programming methods for rainfall prediction and rainfall derivatives pricing". Thesis, University of Kent, 2017. https://kar.kent.ac.uk/69471/.
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Rainfall derivatives is a part of an umbrella concept of weather derivatives, whereby the underlying weather variable determines the value of derivative, in our case the rainfall. These financial contracts are currently in their infancy as they have started trading on the Chicago Mercantile Exchange (CME) since 2011. Such contracts are very useful for investors or trading firms who wish to hedge against the direct or indirect adverse effects of the rainfall. The first crucial problem to focus on in this thesis is the prediction of the level of rainfall. In order to predict this, two techniques are routinely used. The first most commonly used approach is Markov chain extended with rainfall prediction. The second approach is Poisson-cluster model. Both techniques have some weakness in their predictive powers for rainfall data. More specifically, a large number of rainfall pathways obtained from these techniques are not representative of future rainfall levels. Additionally, the predictions are heavily influenced by the prior information, leading to future rainfall levels being the average of previously observed values. This motivates us to develop a new algorithm to the problem domain, based on Genetic Programming (GP), to improve the prediction of the underlying variable rainfall. GP is capable of producing white box (interpretable, as opposed to black box) models, which allows us to probe the models produced. Moreover, we can capture nonlinear and unexpected patterns in the data without making any strict assumptions regarding the data. The daily rainfall data represents some difficulties for GP. The difficulties include the data value being non-negative and discontinuous on the real time line. Moreover, the rainfall data consists of high volatilities and low seasonal time series. This makes the rainfall derivatives much more challenging to deal with than other weather contracts such as temperature or wind. However, GP does not perform well when it is applied directly on the daily rainfall data. We thus propose a data transformation method that improves GP's predictive power. The transformation works by accumulating the daily rainfall amounts into accumulated amounts with a sliding window. To evaluate the performance, we compare the prediction accuracy obtained by GP against the most currently used approach in rainfall derivatives, and six other machine learning algorithms. They are compared on 42 different data sets collected from different cities across the USA and Europe. We discover that GP is able to predict rainfall more accurately than the most currently used approaches in the literature and comparably to other machine learning methods. However, we find that the equations generated by GP are not able to take into account the volatilities and extreme periods of wet and dry rainfall. Thus, we propose decomposing the problem of rainfall into 'sub problems' for GP to solve. We decompose the time series of rainfall by creating a partition to represent a selected range of the total rainfall amounts, where each partition is modelled by a separate equation from GP. We use a Genetic Algorithm to assist with the partitioning of data. We find that through the decomposition of the data, we are able to predict the underlying data better than all machine learning benchmark methods. Moreover, GP is able to provide a better representation of the extreme periods in the rainfall time series. The natural progression is to price rainfall futures contracts from rainfall prediction. Unlike other pricing domains in the trading market, there is no generally recognised pricing framework used within the literature. Much of this is due to weather derivatives (including rainfall derivatives) existing in an incomplete market, where the existing and well-studied pricing methods cannot be directly applied. There are two well-known techniques for pricing, the first is through indifference pricing and the second is through arbitrage free pricing. One of the requirements for pricing is knowing the level of risk or uncertainty that exists within the market. This allows for a contract price free of arbitrage. GP can be used to price derivatives, but the risk cannot be directly estimated. To estimate the risk, we must calculate a density of proposed rainfall values from a single GP equation, in order to calculate the most probable outcome. We propose three methods to achieve the required results. The first is through the procedure of sampling many different equations and extrapolating a density from the best of each generation over multiple runs. The second proposal builds on the first considering contract-specific equations, rather than a single equation explaining all contracts before extrapolating a density. The third method is the proposition of GP evolving and creating a collection of stochastic equations for pricing rainfall derivatives. We find that GP is a suitable method for pricing and both proposed methods are able to produce good pricing results. Our first and second methods are capable of pricing closer to the rainfall futures prices given by the CME. Moreover, we find that our third method reproduces the actual rainfall for the specified period of interest more accurately.
4
Langousis, Andreas 1981. "Extreme rainfall intensities and long-term rainfall risk from tropical cyclones". Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/47737.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2009.Includes bibliographical references (leaves 78-85).
We develop a methodology for the frequency of extreme rainfall intensities caused by tropical cyclones (TCs) in coastal areas. The mean rainfall field associated with a TC with maximum tangential wind speed Vmax, radius of maximum winds Rmax, and translation speed Vmax, is obtained using a physically-based model, whereas rainfall variability at both large scales (from storm to storm) and small scales (due to rainbands and local convection) is modeled statistically. The statistical component is estimated using precipitation radar (PR) data from the TRMM mission. Taylor's hypothesis is used to convert spatial rainfall intensity fluctuations to temporal fluctuations at a given location A. The combined physical-statistical model gives the distribution of the maximum rainfall intensity at A during a period of duration D for a TC with characteristics (Vmax, Rmax, Vt) that passes at a given distance from A. To illustrate the use of the model for long-term rainfall risk analysis, we formulate a recurrence model for tropical cyclones in the Gulf of Mexico that make landfall between longitudes 85°-95°W. We then use the rainfall and recurrence models to assess the rainfall risk for New Orleans. For return periods of 100 years or more and long averaging durations (D around 12-24 hours), tropical cyclones dominate over other rainfall event types, whereas the reverse is true for shorter return periods or shorter averaging durations.
by Andreas Langousis.
Ph.D.
5
Rudberg, Olov, i Daniel Bezaatpour. "Regional Rainfall Frequency Analysis". Thesis, Stockholms universitet, Statistiska institutionen, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-186813.
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Frequency analysis is a vital tool when nding a well-suited probability distributionin order to predict extreme rainfall. The regional frequency approach have beenused for determination of homogeneous regions, using 11 sites in Skane, Sweden. Todescribe maximum annual daily rainfall, the Generalized Logistic (GLO), GeneralizedExtreme Value (GEV), Generalized Normal (GNO), Pearson Type III (PE3),and Generalized Pareto (GPA) distributions have been considered. The method ofL-moments have been used in order to nd parameter estimates for the candidatedistributions. Heterogeneity measures, goodness-of-t tests, and accuracy measureshave been executed in order to accurately estimate quantiles for 1-, 5-, 10-, 50- and100-year return periods. It was found that the whole province of Skane could beconsidered as homogeneous. The GEV distribution was the most consistent withthe data followed by the GNO distribution and they were both used in order toestimate quantiles for the return periods. The GEV distribution generated the mostprecise estimates with the lowest relative RMSE, hence, it was concluded to be thebest-t distribution for maximum annual daily rainfall in the province.
6
Puvaneswaran, Manickam. "A study of rainfall fluctuations in the homogeneous rainfall regimes in Sri Lanka". Thesis, University of Sheffield, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296059.
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Zagrodnik, Joseph P. "Comparison and Validation of Tropical Rainfall Measuring Mission (TRMM) Rainfall Algorithms in Tropical Cyclones". FIU Digital Commons, 2012. http://digitalcommons.fiu.edu/etd/903.
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Tropical Rainfall Measuring Mission (TRMM) rainfall retrieval algorithms are evaluated in tropical cyclones (TCs). Differences between the Precipitation Radar (PR) and TRMM Microwave Imager (TMI) retrievals are found to be related to the storm region (inner core vs. rainbands) and the convective nature of the precipitation as measured by radar reflectivity and ice scattering signature. In landfalling TCs, the algorithms perform differently depending on whether the rainfall is located over ocean, land, or coastal surfaces. Various statistical techniques are applied to quantify these differences and identify the discrepancies in rainfall detection and intensity. Ground validation is accomplished by comparing the landfalling storms over the Southeast US to the NEXRAD Multisensor Precipitation Estimates (MPE) Stage-IV product. Numerous recommendations are given to algorithm users and developers for applying and interpreting these algorithms in areas of heavy and widespread tropical rainfall such as tropical cyclones.
8
To, Chun-hung. "Stochastic model of daily rainfall". Click to view the E-thesis via HKUTO, 1989. http://sunzi.lib.hku.hk/hkuto/record/B31976098.
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Stein, Daniel. "Rainfall index insurance in India". Thesis, London School of Economics and Political Science (University of London), 2011. http://etheses.lse.ac.uk/167/.
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This thesis provides three works which each contribute to understanding of the promising yet struggling market for rainfall index insurance in India. The first chapter contains an analysis of the willingness-to-pay (WTP) for rainfall insurance by poor farmers in Gujarat, India. It develops a theoretical model to predict individual WTP and contrasts it with emprical estimates of WTP using the Becker-DeGroot-Marshalk (BDM) mechanism. We find that BDM works well as a predictor of WTP, but that our model significantly overestimates WTP. The second chapter seeks to provide a possible explanation for demand being lower than theoretical predictions by looking at the dynamics of insurance demand. Using a panel dataset of insurance purchasers in India, it shows that people who receive an insurance payout are 9-22% more likely to purchase insurance the following year. The results are consistent with a dynamic model of insurance demand featuring loss aversion, in which receiving an insurance payout shifts the reference point such that people become more risk averse the following season. I provide evidence against other possible explanations, such as increased trust and learning about insurance, and direct effects of bad weather. The final chapter explores the possibility that combining rainfall insurance with savings may result in a more attractive financial product than insurance on its own. We conduct a laboratory experiment with Indian farmers that uses the BDM mechanism to assess the valuation of various insurance/savings combinations, which we title WISAs (Weather Insured Savings Accounts). We find that, contrary to theoretical predictions, most people prefer both pure savings and pure insurance to any combination of the two. This paper hopefully provides valuable contibutions to solving the puzzle of how to shield poor farmers from uncertain rainfall.
10
To, Chun-hung, i 杜振雄. "Stochastic model of daily rainfall". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1989. http://hub.hku.hk/bib/B31976098.
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Diro, Gulilat Tefera. "Seasonal forecasting of Ethiopian rainfall". Thesis, University of Reading, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.501507.
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Reliable prediction of rainfall in advance of the rainy season would have enormous social and economic benefits to countries such as Ethiopia that depend on rain fed agriculture. This thesis is trying to do two things. Firstly it tries to develop a statistical seasonal forecasts of the Ethiopian rains which could be used operationally. Secondly, it also tries to understand the mechanisms by which the predictors (remote SSTs) are linked to rainfall using observational and modelling studies. Because of the spatial variation in both the interannual variability and the annual cycle of rainfall, Ethiopia was divided into homogeneous rainfall zones, and separate forecasts were developed for each zone. Two techniques (multiple linear regression (MLR) and linear discriminant analysis (LOA» were applied to four sets of predictors (selected by either stepwise regression or discriminant analysis either including or excluding the contemporaneous season). All the forecasts had more skill than either a random or climatological forecast. For all forecasts, the extreme years (very rainy and very dry) were more reliably forecast than average years. The mechanisms for the link between SSTs and rainfall were studied using observational analysis and modelling experiments. In the observational analysis, two sets of composites were analysed. The first set of composites was composites of atmospheric fields based on excess and deficit rainfall years which were meant to identify the large scale atmospheric variables responsible for rainfall variability. The second set was also composites of global atmospheric fields but based on warm and cold SST of the oceanic regions used as predictors in the forecasting models. This analysis aimed to identify the link between the remote SST and the rainfall via large scale atmospheric features. In the Modelling experiments, an ensemble of atmosphere only GeM (HadAM3) integrations were done by forcing with observed and idealised SST anomaly patterns. The observed SST forced run is intended to examine whether the model captures some of the observed interannual variability of rainfall related to fluctuation in the SST. The idealised SST pattern forced experiment is done in order to understand the sensitivity of atmospheric circulations to various locations of SST forcing. The result from the idealised experiment shows that warming of equatorial Pacific directly affects Ethiopian rainfall by among other things, weakening the tropical easterly jet and reducing the influx of moisture from the Atlantic and Indian oceans.
12
Driver, Penny Meredith. "Rainfall variability over southern Africa". Doctoral thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/12830.
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Includes bibliographical references.Southern Africa is subject to high inter annual rainfall variability and the factors influencing southern African rainfall are not fully understood. The variability has been linked with various sea surface temperature anomalies (SSTAs) in each of the three major ocean basins as well as variability in the strength and position of regional atmospheric features. One of the atmospheric factors that may play a substantial role in southern African rainfall variability is the Botswana high, a high pressure cell which exists at the 500hPa level and is centred over central Namibia and western Botswana during austral summer. 20th Century reanalysis data is used to further investigate this feature and analysis reveals an association between the strength of the Botswana high and ENSO. Further analysis indicates that a connection between the Botswana high and rainfall over southern Africa not only exists during ENSO years, but is also apparent during neutral years that display ENSO-like characteristics in the Botswana high. This result may assist in producing better rainfall forecasts for non-ENSO years. The frequency of dry days over southern Africa during austral summer is investigated using GPCP observational data. Correlation analysis is generally in agreement with previous studies and showed that dry day frequency(DDF) over the Limpopo and North East Zambia regions is correlated with ENSO, while DDF over coastal northern Angola and central South Africa is correlated with SSTs in the Indian and Atlantic Oceans. The possible role played by DDF during JFM 1998 and JFM 2010 is investigated and results indicate that the distribution of DDF over southern Africa was notably different during these two seasons and may have contributed to the unexpected rainfall experienced over southern Africa.
13
Riverso, Carlo. "Calibration of rainfall-runoff models". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amslaurea.unibo.it/2619/.
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Mongwa, Themba. "Rainfall intensity, kinetic energy and erosivity of individual rainfall events on the island of Mauritius". Thesis, University of Fort Hare, 2011. http://hdl.handle.net/10353/452.
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On most tropical volcanic islands the risk for soil erosion is enhanced due to a complex topography, high intensity rainfall and the exploitation of land for agriculture. Mauritius is a typical maritime tropical volcanic island with a distinct elevated interior. Rainfall is dominated by tropical weather systems and trade winds and the island is under intensive cultivation. Rainfall depth, duration, intensity, kinetic energy and erosivity were analysed for 385 erosive rainfall events at five locations over a five year period (2004 to 2008) on the island of Mauritius. Two stations located on the west coast and three stations sited on the Central Plateau above 550 m a.s.l. are used to provide detailed rainfall data at six minute intervals. Erosive storm events, defined here as a total rainfall exceeding 12.5 mm and a maximum 6-minute intensity exceeding 25 mm/hour, are found to differ markedly between the coastal lowlands and the elevated interior with regards to the frequency, the total rainfall generated, the duration, total kinetic energy and total erosivity of individual events. However, mean kinetic energy, mean and maximum rainfall erosivity (EI30) and maximum intensities (I30) from individual erosive events do not show this distinct differentiation. Erosivity measured during summer exceeds that recorded in winter, but the data indicate that large percentages of winter rainfall on Mauritius are defined as erosive and non-tropical cyclone rainfall can pose a substantial erosion risk. In this maritime tropical environment with its elevated interior, soil erosion risk occurs from storm scale to synoptic scale rainfall events and extreme events generate the bulk of the erosivity. Findings show that using rainfall records at an event scale within soil erosion risk assessments on tropical islands with a complex topography will increase the effectiveness of erosivity estimates
15
Gilmore, William T. "Comparison of rainfall energy and soil erosion parameters from a rainfall simulator and natural rain". Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/5101.
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Thesis (M.S.)--University of Missouri-Columbia, 2007.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on October 25, 2007) Vita. Includes bibliographical references.
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Szyniszewska, Anna Maria. "Determining the daily rainfall characteristics from the monthly rainfall totals in central and northeastern Thailand". [Gainesville, Fla.] : University of Florida, 2009. http://purl.fcla.edu/fcla/etd/UFE0025162.
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Van, Cooten Suzanne. "Statistical Analysis of Seasonal Precipitation for the Lake Pontchartrain Basin and Associated Watersheds". ScholarWorks@UNO, 2005. http://scholarworks.uno.edu/td/154.
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To investigate seasonal patterns of precipitation, statistical analysis was performed on a dataset of daily rainfall observed at 63 south Louisiana stations from 1836 to 2002. Each station record was examined for data quality and continuity with special attention to time periods surrounding station relocation or equipment exchange. Mean Areal Precipitation (MAP) sheets were compiled for every month from 1836 to 2002 to document the daily rainfall across south Louisiana and neighboring portions of southern and coastal Mississippi. Using these MAP sheets, missing data was examined to see if a reasonable value could be substituted to extend the continuity of a station's rainfall record. Once these data quality and continuity checks were completed, a series of statistical tests were conducted to determine an accurate scheme to form station groups. To group stations together, each station was required to have a normal distribution of monthly average rainfall, a statistically equivalent variance, and a statistically equivalent mean when compared with other stations in the group. As a result of the Shapiro-Wilk Test, the F-Test, and the Student T-test, eight station groups were formed. To define seasonal rainfall patterns across south Louisiana, statistical tests were conducted for a 12 month period and six and three month intervals. For the six month intervals, group rainfall averages and pooled variances were calculated for each interval beginning with January-July and ending with December-May. For the three month intervals, group rainfall averages and pooled variances were calculated for January-March and concluded with December-February. To test the hypothesis of a statistically significant difference in mean rainfall between the eight groups for a 12, six, and three month period, the Student T-test was conducted. For an annual basis, there is a statistically significant difference in average rainfall at a five percent level of significance between all of the groups except the Southshore (S.S) group when compared to the SW1 group. For six and three month intervals, statistically significant differences exist between the eight groups especially during winter and segments of the Hurricane season from June to November.
18
Eckersten, Sofia. "Updating Rainfall Intensity-Duration-Frequency Curves in Sweden Accounting for the Observed Increase in Rainfall Extremes". Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-283714.
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Increased extreme precipitation has been documented in many regions around the world, in- cluding central and northern Europe. Global warming increases average temperature, which in turn enhances atmospheric water holding capacity. These changes are believed to increase the frequency and/or intensity of extreme precipitation events. In determining the design storm, or a worst probable storm, for infrastructure design and failure risk assessment, experts commonly assume that statistics of extreme precipitation do not change significantly over time. This so- called notion of stationarity assumes that the statistics of future extreme precipitation events will be similar to those of historical observations. This study investigates the consequences of using a stationary assumption as well as the alternative: a non-stationary framework that con- siders temporal changes in statistics of extremes. Here we evaluate stationary and non-stationary return levels for 10-year to 50-year extreme precipitation events for different durations (1-day, 2-day, ..., 7-day precipitation events), based on the observed daily precipitation from Sweden. Non-stationary frequency analysis is only considered for stations with statistically significant trends over the past 50 years at 95% confidence (i.e., 15 to 39 % out of 139 stations, depend- ing on duration, 1-day, 2-day, ..., 7-day). We estimate non-stationary return levels using the General Extreme Value distribution with time-dependent parameters, inferred using a Bayesian approach. The estimated return levels are then compared in terms of duration, recurrence in- terval and location. The results indicate that a stationary assumption might, when a significant trend exists, underestimate extreme precipitation return levels by up to 40 % in Sweden. This report highlights the importance of considering better methods for estimating the recurrence in- terval of extreme events in a changing climate. This is particularly important for infrastructure design and risk reduction.Ökad extrem nederbörd har dokumenterats globalt, däribland centrala och norra Europa. Den globala uppvärmningen medför en förhöjd medeltemperatur vilket i sin tur ökar avdunstning av vatten från ytor samt atmosfärens förmåga att hålla vatten. Dessa förändringar tros kunna öka och intensifiera nederbörd. Vid bestämning av dimensionerande nederbördsintensiteter för byggnationsprojekt antas idag att frekvensen och storleken av extrem nederbörd inte kommer att förändras i framtiden (stationäritet), vilket i praktiken innebär ingen förändring i klimatet. Den här studien syftar till att undersöka effekten av en icke-stationärt antagande vid skattning av dimensionerande nederbördsintensitet. Icke-stationära och stationära nerderbördsintensiteter föråterkomsttider mellan 10 och 100år bestämdes utifrån daglig och flerdaglig svensk nederbörds- data. Nederbördintensiteterna bestämdes med extremvärdesanalys i mjukvaran NEVA, där den generella extremvärdesfördelningen anpassades till årlig maximum nederbörd på platser i Sverige som påvisade en ökande trend under de senaste 50åren (15% till 39 % utav 139 stationer, beroende på varaktighet). De dimensionerande nederbördsintensiteterna jämfördes sedan med avseende på varaktighet, återkomsttid och plats. Resultaten indikerade på att ett stationärt antagande riskerar att underskatta dimensionerande nederbördsintensiteter för en viss återkomsttid med upp till 40 %. Detta indikerar att antagandet om icke-stationäritet har större betydelse för olika platser i Sverige, vilket skulle kunna ge viktig information vid bestämning av dimensionerande regnintensiteter.
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Hussain, Arshad. "Stochastic modeling of rainfall processes: a Markov chain - mixed exponential model for rainfalls in different climatic conditions". Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18710.
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Watershed models simulating the physical process of runoff usually require daily or sub-daily rainfall time series data as input. However, even when rainfall records are available, they contain only limited and finite information regarding the historical rainfall pattern to adequately assess the response and reliability of a water resource system. This study is therefore concerned with the development of a stochastic rainfall model that can reliably generate many sequences of synthetic rainfall time series' that have similar properties to those of the observed data. The 'MCME' model developed is based on a combination of the rainfall occurrence (described using a Markov Chain process) and the distribution of rainfall amounts on wet days (represented by the Mixed-Exponential probability function). Various optimization methods were tested to best calibrate the model's parameters and the model was then applied to daily rainfall data from 3 different regions across the globe (Dorval, Quebec, Sooke Reservoir in British Columbia and Roxas City in the Philippines) to assess the accuracy and suitability of the model for daily rainfall simulation. The feasibility of the MCME model was also assessed using hourly rainfall data available at Dorval Airport in Quebec (Canada). In general, it was found that the proposed MCME model was able to adequately describe various statistical and physical properties of the daily and hourly rainfall processes considered. In addition, an innovative approach was proposed to combine the estimation of daily annual maximum precipitations (AMPs) by the MCME with those by the downscaled Global Circulation Models (GCMs). The combined model was found to able to provide AMP estimates that were comparable to the observed values at a local site. In particular, the suggested linkage between the MCME and downscaled-GCM outputs would be useful for various climate change impact studies involving rainfall extremes.La précipitation est souvent considérée comme la composante d'entrée principale pour les modèles de simulation de ruissellement. Toutefois, même si les donnés de précipitation sont disponibles, ces données ne contiennent qu'une quantité d'information limitée concernant la variabilité de précipitation dans le passé. La présente étude a alors pour objet d'élaborer un modèle stochastique de précipitation qui est capable de générer plusieurs séries synthétiques de précipitation ayant les mêmes propriétés statistiques et physiques que les données historiques. Le modèle MCME proposé dans cette étude consiste a une combinaison de la composante d'apparition de pluie (représentée par la chaîne de Markov) et la composante de répartition de quantité de précipitation (représentée par la loi exponentielle mixte). L'évaluation de la faisabilité et de la précision de ce modèle a été effectuée en utilisant les données de précipitations journalières disponibles en trois sites situés dans trois régions différentes du monde et en utilisant plusieurs méthodes de calibration par les techniques d'optimisation locale et globale. La faisabilité du modèle MCME a été également évaluée avec les données de précipitation horaire disponibles a l'aéroport de Dorval au Québec (Canada). En général on a trouvé que le modèle MCME est capable de décrire adéquatement diverses propriétés statistiques et physiques des processus de précipitations journalier et horaire considérés. En plus, une approche innovatrice a été suggérée pour combiner l'estimation des précipitations annuelles maximales par le modèles MCME avec celles fournies par la mise en échelle des modèles de circulation globale (GCM). On a trouvé que les modèles combinés sont capable du calculer les précipitations annuelles maximales qui sont comparables aux valeurs observées en un site donné. En particulier la connection entre le modèle MC
20
Wolf, Linden S. "Statistical forecasting of Florida monthly rainfall". Tallahassee, Florida : Florida State University, 2009. http://etd.lib.fsu.edu/theses/available/etd-08242009-163026/.
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Thesis (M.S.)--Florida State University, 2009.Advisor: Jon E. Ahlquist, Florida State University, College of Arts and Sciences, Dept. of Meteorology. Title and description from dissertation home page (viewed on May 11, 2010). Document formatted into pages; contains x, 42 pages. Includes bibliographical references.
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Abushandi, Eyad. "Rainfall-runoff modeling in arid areas". Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2011. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-68530.
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The Wadi Dhuliel catchment/ North east Jordan, as any other arid area has distinctive hydrological features with limited water resources. The hydrological regime is characterized by high variability of temporal and spatial rainfall distributions, flash floods, absence of base flow, and high rates of evapotranspiration. The aim of this Ph.D. thesis was to apply lumped and distributed models to simulate stream flow in the Wadi Dhuliel arid catchment. Intensive research was done to estimate the spatial and temporal rainfall distributions using remote sensing. Because most rainfall-runoff models were undertaken for other climatic zones, an attempt was made to study limitations and challenges and improve rainfall-runoff modeling in arid areas in general and for the Wadi Dhuliel in particular.
The thesis is divided into three hierarchically ordered research topics. In the first part and research paper, the metric conceptual IHACRES model was applied to daily and storm events time scales, including data from 19 runoff events during the period 1986-1992. The IHACRES model was extended for snowfall in order to cope with such extreme events. The performance of the IHACRES model on daily data was rather poor while the performance on the storm events scale shows a good agreement between observed and simulated streamflow. The modeled outputs were expected to be sensitive when the observed flood was relatively small. The optimum parameter values were influenced by the length of a time series used for calibration and event specific changes.
In the second research paper, the Global Satellite Mapping of Precipitation (GSMaP_MVK+) dataset was used to evaluate the precipitation rates over the Wadi Dhuliel arid catchment for the period from January 2003 to March 2008. Due to the scarcity of the ground rain gauge network, the detailed structure of the rainfall distribution was inadequate, so an independent from interpolation techniques was used. Three meteorological stations and six rain gauges were used to adjust and compare with GSMaP_MVK+ estimates. Comparisons between GSMaP_MVK+ measurements and ground rain gauge records show distinct regions of correlation, as well as areas where GSMaP_MVK+ systematically over- and underestimated ground rain gauge records. A multiple linear regression (MLR) model was used to derive the relationship between rainfall and GSMaP_MVK+ in conjunction with temperature, relative humidity, and wind speed. The MLR equations were defined for the three meteorological stations. The ‘best’ fit of the MLR model for each station was chosen and used to interpolate a multiscale temporal and spatial distribution. Results show that the rainfall distribution over the Wadi Dhuliel is characterized by clear west-east and north-south gradients. Estimates from the monthly MLR model were more reliable than estimates obtained using daily data. The adjusted GSMaP_MVK+ dataset performed well in capturing the spatial patterns of the rainfall at monthly and annual time scales, while daily estimation showed some weakness for light and moderate storms.
In the third research paper, the HEC-HMS and IHACRES rainfall runoff models were applied to simulate a single streamflow event in the Wadi Dhuliel catchment that occurred in 30-31.01.2008. Both models are considered suitable for arid conditions. The HEC-HMS model application was done in conjunction with the HEC-GeoHMS extension in ArcView 3.3. Streamflow estimation was performed on hourly data. The aim of this study was to develop a new framework of rainfall-runoff model applications in arid catchment by integrating a re-adjusted satellite derived rainfall dataset (GSMaP_MVK+) to determine the location of the rainfall storm. Each model has its own input data sets. HEC-HMS input data include soil type, land use/land cover map, and slope map. IHACRES input data sets include hourly rainfall and temperature. The model was calibrated and validated using observed stream flow data collected from Al-Za’atari discharge station. IHACRES shows some weaknesses, while the flow comparison between the calibrated streamflow results agrees well with the observed streamflow data of the HEC-HMS model. The Nash-Sutcliffe efficiency (Ef) for both models was 0.51, and 0.88 respectively. The application of HEC-HMS model in this study is considered to be satisfactory.
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Asadian, Yeganeh. "Rainfall interception in an urban environment". Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/23517.
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Vegetation interception loss plays an important role in controlling the water balance of a watershed, especially where urban development has taken place. The aim of this study is to document the importance of urban trees as a form of ‘green infrastructure’ to reduce stormwater runoff and rainwater intensity, and cause a delay in precipitation reaching the ground. A 21 months study was carried out in the North/West Vancouver in British Columbia to determine how effective urban trees are to intercept and detain rainwater. We applied a unique methodology for measuring rain/throughfall under 54 different urban trees using a system of PVC pipes hung beneath the canopy to capture the throughfall where it drained into a rain gauge attached to a data logger. To ensure that the study adequately captured the range of throughfall variability, trees were selected to sample different landscape sites (streets, parks, and natural forested areas), elevations, tree type, health condition and species, including Douglas-fir (Pseudotsuga menziesii), Western red cedar (Thuja plicata), Bigleaf maple (Acer macrophyllum), Oak (Quercus sp.), Copper beech (Fagus sylvatica), Horse chestnut (Aesculus hippocastanum), Cherry (Prunus sp.), and Poplar (Populus sp.). Interception loss and throughfall were monitored from February 2007 until November 2008. Rainfall interception varied seasonally for all species. Interception losses accounted for on average 76.5% and 56.4% of gross precipitation for coniferous and deciduous trees, respectively. The interception loss varied depending on canopy structure, climatic conditions, and rainfall characteristics. The results showed that urban trees intercept and evapotranspire more rain than trees in forested environments. Together with the delay in runoff trees can act as an effective stormwater management tool on individual properties.
23
Nguyen, Tan Danh. "Regional estimation of extreme rainfall events". Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84300.
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The first part of the research deals with the estimation of extreme rainfalls for locations where rainfall records are sufficiently available (gaged sites); the second part is concerned with cases where rainfall data are limited (partially-gaged sites); and finally the third part involves the most complex situation where rainfall data are unavailable (ungaged sites).For gaged sites, two methods were developed for estimating the annual extreme (AE) rainfalls based on the simple scaling behaviour of the first three non-central moments (NCMs) of the AE rainfall processes and using the Generalized Extreme Value (GEV) distribution as the parent distribution. The first estimation method was called one-moment (OM) method since it only relied on the first-order NCM of AE rainfall series in the computation of the rainfall quantiles, while the second method was called three-moment (TM) procedure since it used all first three NCMs of AE rainfalls in the estimation of the quantiles.
For partially-gaged and ungaged sites, a new approach to defining rainfall homogeneous regions has been proposed based on the similarity of rainfall occurrences at different raingage stations. In addition, a Principal Component Analysis technique was used to assess the similarity of raingages and to delineate homogeneous regions.
On the basis of the proposed method for identifying rainfall homogeneous regions, two new methods (PG-1 and PG-2) were developed for estimating annual maximum (AM) rainfalls at partially gauged sites. These methods were also based on the scaling properties of AM rainfall series for different durations.
For ungaged sites, three methods (UG-1, UG-2, and NR) were proposed for estimating AM rainfalls. Method UG-1 was based on the NCMs of AM rainfalls at an ungaged site that were computed by direct interpolation of the corresponding NCM values from the gaged sites within the same homogeneous region. Method UG-2 used the pooled data set from all gaged sites in the homogeneous region for this computation. On the other hand, the NR method estimated the NCMs of AM rainfalls for an ungaged site using the regional regression between the first three NCMs and the number of rainfall occurrence (NR) values that were interpolated from the NR values of the gaged sites.
Finally, to assess the uncertainty of extreme rainfall estimates, two new methods (CI-1 and CI-2) were developed for computing the confidence limits (CLs) based on these estimated values. The proposed methods were based on the bootstrap technique and the scaling properties of the NCMs of extreme rainfall series.
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Seed, Alan William. "Statistical problems in measuring convective rainfall". Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74251.
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Simulations based on a month of radar data from Florida, and a summer of radar data from Nelspruit, South Africa, were used to quantify the errors in the measurement of mean areal rainfall which arise simply as a result of the extreme variability of convective rainfall, even with perfect remote sensing instruments. The raingauge network measurement errors were established for random and regular network configurations using daily and monthly radar-rainfall accumulations over large areas. A relationship to predict the measurement error for mean areal rainfall using sparse networks as a function of raining area, number of gauges, and the variability of the rainfield was developed and tested. The manner in which the rainfield probability distribution is transformed under increasing spatial and temporal averaging was investigated from two perspectives. Firstly, an empirical relationship was developed to transform the probability distribution based on some measurement scale, into a distribution based on a standard measurement length. Secondly, a conceptual model based on multiplicative cascades was used to derive a scale independent probability distribution.
25
Preece, David John. "Decadal rainfall variability over Southern Africa". Thesis, University College London (University of London), 2008. http://discovery.ucl.ac.uk/17232/.
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Southern Africa is a region of vulnerability, with high seasonal and interannual rainfall variability combined with rain-dependent agriculture. This variability is underpinned by influences from ENSO and other oceanic forcing, and known to exhibit quasi-decadal variability at 16-20 years (Tyson, 1975). This study uses a combination of proxy, observed and climate model data to explore the nature, mechanisms and anthropogenic forcing of rainfall variability at decadal scales. The spatial nature of rainfall variability, demonstrated through EOF analysis and composite decadal events, is similar to that at interannual scales. Spectral analysis of observed data confirms the presence of variability at ENSO-related timescales, combined with influences in the 10-12 year and 16-20 year band. Subtle differences appear in model simulated rainfall. The mechanisms of quasi-decadal variability are also shown to be similar to interannual forcing patterns: showing links to ENSO, the tropical and South Atlantic oceans, and the South West Indian Ocean. Rainfall correlation at decadal scales is dominated by the SW Indian Ocean, but the ‘dipole’ like forcing observed at interannual timescales is notable less coherent at quasi-decadal scales. Model-specific differences are explored, and though to be the result of the interaction between a weak (strong) decadal ENSO signal and a strong (weak) Southern Annular Mode influence at multi-decadal timescales. Using state of the art model simulations (Gonzales-Rouco et al., 2003; Tett et al., 2007) that incorporate anthropogenic forcings, the study also explores the impact of climate change on the quasi-decadal signals over the region. Results show that quasi-decadal variability is damped under anthropogenic forcing. The spatial structure appears unaltered, and many of the mechanisms are consistent with those in unforced simulations. A key change occurs in the tropical Indian Ocean, which substantially alters in relationship with the southern African rainfall. Implications for decadal predictability over the region are discussed and evaluated.
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Thompson, Robert John. "Rainfall estimation using polarimetric weather radar". Thesis, University of Reading, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493986.
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Rainfall is a key observable of the weather, of importance to society. Rain gauges only provide point measurements; for areal rainfall information a radar may be used. Radars measuring just reflectivity (Z) may suffer large errors in derived rainrates due to drop size distribution (DSD) variations. The introduction of dual-polarisation radars to operational networks should lead to improvements in rainfall estimation, although these radars suffer high noise levels in polarisation parameters (~ 0.7 dB in differential reflectivity [ZDR]).
27
Smith, Elizabeth. "Bayesian modelling of extreme rainfall data". Thesis, University of Newcastle Upon Tyne, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.424142.
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Kakou, Anastasia. "Point process based models for rainfall". Thesis, University College London (University of London), 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266073.
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29
Chen, Yi-Ting Civ E. Massachusetts Institute of Technology. "Rainfall-induced Landslide Hazard Rating System". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/66858.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 136-138).
This research develops a Landslide Hazard Rating System for the rainfall-induced landslides in the Chenyulan River basin area in central Taiwan. This system is designed to provide a simplified and quick evaluation of the possibility of landslide occurrence, which can be used for planning and risk management. A systematic procedure to investigate the characterization of rainfall distribution in a regional area is developed in the first part of the thesis. Rainfall data for approximately one decade, 2002 to 2008, from 9 rainfall stations in the study area are included, in which a total of 46 typhoons are selected and categorized into 3 typhoon paths: the Northeastern, Northwestern, and Western. The rainfall distribution affected by typhoon paths in a region is thereby determined. The second part of the thesis is the Landslide Hazard Rating System, which integrates different hazard factors: bedrock geology, aspect, and slope gradients. This analysis is based on the specific characterization of the study area, which consists of the relative topographic relief (aspect and slope gradients) and variable bedrock geology. The method of normalized difference is used for examining the relationship of the topographic features to landslide occurrence. Although this study is conducted in a specific area, this landslide hazard rating system can be applied to other locations. Finally, a concept of a rainfall-induced landslide analytical system is proposed to combine the rainfall distribution analysis and the landslide hazard rating system. This analytical system is intended to include and address the relationship of rainfall and landslide occurrence by combining characterizations of rainfall, topography, and landslide potential. Additionally, this study recommends that, in future work, theoretical models of rainfall distribution and laboratory tests of soil and rock samples be included. Together, these will constitute a basis for the prediction of landslide occurrence. The ultimate goal of future work should be the development of a system for assessing and forecasting rainfall-induced landslide risks, which can become the foundation for a comprehensive risk management system for use in planning.
by Yi-Ting Chen.
S.M.
30
Wright, Winfield G. "Modeling karst aquifer response to rainfall". Thesis, Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/76043.
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A finite-element model (HYDMATCH) uses spring hydrograph discharge data to generate a linear regression relation between fracture conductivity and potential gradient in a karst aquifer system. Rainfall excess in the form of potential energy from sinkhole sub-basins is input to element nodes and routed through a one-dimensional finite-element mesh to the karst spring represented by the last node in the finite element mesh. A fracture-flow equation derived from the Navier-Stokes equation uses fracture conductivities from the regression equation and potential gradient in the last element of the mesh to determine discharge at the spring.
Discharge hydrograph data from Nininger spring, located in Roanoke, Virginia, was used to test the performance of the model. Excess from a one-half inch rain was introduced into sinkhole nodes and the regression equation generated by matching discharges from the known hydrograph for the one-half inch rainfall. New rainfall excess data from a one-inch rainfall was input to the sinkhole nodes and routed through the finite-element mesh. The spring hydrograph for the one-inch rainfall was calculated using the regression equation which was determined previously. Comparison of the generated hydrograph for the one-inch rainfall to a known hydrograph for a one-inch rainfall shows similar shapes and discharge values.
Areas in need of improvement in order to accurately model ground-water flow in karst aquifers are a reliable estimate of rainfall excess, a better estimation of baseflow and antecedent aquifer conditions, and the knowledge of the karst aquifer catchment boundaries. Models of this type may then be useful to predict flood discharges and contaminant travel times in karst aquifers.Master of Engineering
31
Tierney, Jessica E., Francesco S. R. Pausata i Peter B. deMenocal. "Rainfall regimes of the Green Sahara". AMER ASSOC ADVANCEMENT SCIENCE, 2017. http://hdl.handle.net/10150/622881.
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During the "Green Sahara" period (11,000 to 5000 years before the present), the Sahara desert received high amounts of rainfall, supporting diverse vegetation, permanent lakes, and human populations. Our knowledge of rainfall rates and the spatiotemporal extent of wet conditions has suffered from a lack of continuous sedimentary records. We present a quantitative reconstruction of western Saharan precipitation derived from leaf wax isotopes in marine sediments. Our data indicate that the Green Sahara extended to 31 degrees N and likely ended abruptly. We find evidence for a prolonged "pause" in Green Sahara conditions 8000 years ago, coincident with a temporary abandonment of occupational sites by Neolithic humans. The rainfall rates inferred from our data are best explained by strong vegetation and dust feedbacks; without these mechanisms, climate models systematically fail to reproduce the Green Sahara. This study suggests that accurate simulations of future climate change in the Sahara and Sahel will require improvements in our ability to simulate vegetation and dust feedbacks.
32
Al-Qurashi, Aisha Mufti Al-Sayyid Hassan. "Rainfall-runoff modelling in arid areas". Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/8860.
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Arid areas have distinctive hydrological features substantially different from those of humid areas. The high temporal and spatial distribution of the ra;infall, flash floods, absence of base flow, sparsity of plant cover, high transmission losses, high amounts of evaporation and evapotranspiration and the general climatologies are examples of such differences. The aim of this Ph.D. research is to use advanced tools of model analysis to test some of the current models that consider arid area hydrological characteristics. As most models were mainly developed for other regions, an attempt is made to study their limitations using Omani hydrological data, providing some guidelines for improved rainfall-runoff modelling in arid areas in general and Oman in particular. Two different types of models were selected for this research; KINEROS, which is an event based, semi-distributed, physically-based model that is considered suitable to be used for arid area conditions, and, which is continuous, lumped, conceptual model. Two Omani catchments were selected to test the performance of the selected models and to identify the main uncertainties arising, to provide some recommendations regarding the suitability of these models or model types and how they might be improved, to highlight any further data that is required, and how uncertainties should be handled in model applications.
33
Farr, C. "Earlier Timing Can Reduce Rainfall Losses". College of Agriculture, University of Arizona (Tucson, AZ), 1989. http://hdl.handle.net/10150/204836.
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The analysis of grades of upland cotton picked before and after a 29 October rainfall at Waddell in 1987 reveals significant financial losses for growers. Early harvesters in the area harvested over two thirds of the crop in October; over 98.0% of grades 21 and 31 were harvested before the rainfall. A Buckeye operation also accounted for a difference of $98.60 per acre between an early and a late harvested pima field the same season. The survey indicates that important losses can be reduced by a harvest begun 10 to 15 days earlier than mid- October.
34
Gill, Tarun Deep. "Transformation of point rainfall to areal rainfall by estimating areal reduction factors, using radar data, for Texas". Texas A&M University, 2005. http://hdl.handle.net/1969.1/2420.
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Information about extreme precipitation is of great interest for a variety of
purposes, which include dam design and its operation, public safety, engineering projects
concerned with river management and drainage as well as rainfall-runoff relations. These
require knowledge about the spatial and temporal variability of average rainfall over an
area. Design rainfall values are generally expressed in the form of point rainfall intensity
values which is the rainfall depth at a location. In order to obtain areal average values for
an area, hydrologists and engineers require techniques whereby point rainfall amounts
can be transformed to average rainfall amounts over a specified area. This problem of
point-to-area rainfall conversion can be addressed using depth??area curves which require
the use of areal reduction factors. The derivation of areal reduction factors is a focal issue
and has been dealt with in diverse manners. Though the methods of derivation of the
areal reduction factors vary, results shown by them are comparable. But all these methods
have certain shortcomings in the procedures adopted by them. In this application the
analysis is based on radar rainfall values obtained from NEXRAD for the study area of
Texas as provided by West Gulf River Forecasting Centre (WGRFC). Using NEXRADradar rainfall data, geographically fixed depth area relationships will be determined. Here
the objectives are to develop areal reduction factors using radar data and to identify the
potential obstacles that might hinder the use of such data. The values of the factors
developed will be finally compared to other studies which have been carried out. This
approach aims to mitigate the difficulties faced in the applications of various procedures
and the shortcomings of the various techniques used to determine the values of areal
reduction factors.
35
Greatrex, Helen. "The application of seasonal rainfall forecasts and satellite rainfall estimates to seasonal crop yield forcasting for Africa". Thesis, University of Reading, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.578012.
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Rain-fed agriculture is extremely important in sub-Saharan Africa, thus the ability to forecast and monitor regional crop yields throughout the growing season would be of enormous benefit to decision makers. Of equal importance to be able to assign a measure of uncertainty to the forecast, especially considering that many predictions are made in the context of a complex climate and sparse meteorological and agricultural observations. This work investigates these issues in the context of an operational updating regional crop yield forecast, concentrating in particular on a case study forecasting Ethiopian maize. Part 1 of the work presented a detailed discussion of Ethiopia' s climate and agricultural systems. As real-time ground based weather observations are sparse in Africa, Part 2 contains an investigation into remotely sensed satellite rainfall estimates. A daily TAMSAT calibration and the geostatistical process of sequential simulation were used to create a spatially correlated ensemble of Meteosat-derived rainfall estimates. The ensemble mean was evaluated as a daily deterministic rainfall product and was found to be as good as or better than other products applied in the same region. A validation of the full ensemble showed that they realistically estimated Ethiopian rainfall fields that agreed both with observed spatial correlations and input pixel level statistics. Part 3 of the work includes a discussion on regional crop simulation modelling and presents a new parameterisation of the GLAM crop simulation model for tropical maize. GLAMMAIZE was then driven using individual members of the satellite ensemble; this was shown to exhibit the correct sensitivities to climate inputs and performed reasonably against yield observations. Finally, Part 4 presented a new method of creating stochastic spatially and temporally correlated rainfall fields. This 'regional weather generator' was tested using a case study on Ethiopian April rainfall and a detailed discussion was included about future development plans.
36
顏遠騰. "Hourly rainfall generator for short-duration rainfall event". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/15462135585509079882.
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Chen, Chia-Jung, i 陳嘉榮. "A Study on Regional Rainfall Analysis and Rainfall-Runoff Forecasting". Thesis, 2000. http://ndltd.ncl.edu.tw/handle/53250698604048877126.
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博士國立成功大學
水利及海洋工程學系
88
This thesis aims to study hydrological design and hydrological forecasting, which are important subjects in water resource engineering. Three parts including regional IDF analysis, rainfall and runoff forecasting are respectively investigated. The results of both hydrological design and forecast in this study are expected to predict the risk of hydraulic structure during typhoon period. The first part of this thesis attempts to develop the regional IDF analysis for ungauged site, which is common problem in hydrological design. Rainfall records from 38 stations in Northern Taiwan provide the data set to develop regional rainfall intensity formula using regional analysis method. This work classifies the Northern Taiwan into three homogeneous regions, which can respond the characteristic of climate and topography on each region. The dimensionless rainfall intensity-duration-frequency (IDF) curves are then established in each homogeneous region. The parameters of dimensionless IDF curve can be regionalizied to generate the regional rainfall intensity-duration-frequency formula, which can reasonably simulate the IDF relationship at ungauged site from the results of calibration and verification. The uncertainty analysis of regional IDF formulae are further investigated based on the method of mean first order second moment (MFOSM). This work reveals that the IDF relationship estimated by using the distribution of extreme value type I can be located into the 95% confidence intervals of uncertainty analysis of regional IDF formula. In the hydrological forecasting, the main purpose of the second part is to study rainfall forecasting during the typhoon period, including a long-term (24 hours ahead) and a short-term (3 hours ahead) rainfall forecast models separately. The long-term forecasting model attempts to forecast 24 hours rainfall hyetograph for a typhoon based on optimal 24 hours rainfall pattern decision and 24 hours rainfall depth prediction. Optimal rainfall pattern for a typhoon is decided based on both typhoon characteristics and historical databases of various rainfall patterns. The databases for four rainfall patterns of Huff are first generated from historical rainfall storm of typhoon events by using fuzzy classification method. The typhoon characteristics including central pressure, central velocity, cyclonic radius and moving path are chosen as variables to decide optimal rainfall pattern for a typhoon approaching to Taiwan by using fuzzy multi-object decision method. 24 hours rainfall depth is further statistically and dynamically predicted by using typhoon characteristic including typhoon path (central position, moving direction) , central pressure, central velocity and cyclonic radius as decision-making variables. The calibration results conclude that the proposed model can reasonably forecast 24 hours rainfall hyetograph for a typhoon event. Regarding to the short-term rainfall forecast model, 3 hours ahead rainfall is forecasted based on both grey system theory and one-time step forecasting technique. The model parameters are calibrated by using fuzzy goal regression. A grey rainfall-runoff model is developed in the third part of this thesis. The model can provide 1~4 hours ahead runoff forecasting in union with rainfall forecasting model developed in the second part. An error prediction model proposed in this study is found to be useful for updating the forecasting results.
38
Chen, Bo-Yu, i 陳柏宇. "Rainfall Frequency Analysis Using Mixture Distribution of Event-Maximum Rainfall Series". Thesis, 2019. http://ndltd.ncl.edu.tw/handle/n5dytw.
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碩士國立臺灣大學
統計碩士學位學程
107
The Annual Maximum Series (AMS) method is a conventional way of conducting rainfall frequency analysis, which plays a crucial role in hydrology engineering in terms of hydrological risk assessment. Given any design duration, the method retrieves only the maximum rainfall within a year and approximate the Annual Maximum Rainfall (AMR) distribution by the Generalized Extreme Value (GEV) distribution according to the Extremal Types Theorem. However, the GEV approximation is inappropriate since AMS is prone to have insufficient sample size and does not take storm events and storm types into account. To overcome the above problems, the Event Maximum Series (EMS) method is proposed. The EMS method classifies storm events in Taiwan into Typhoon, Meiyu, frontal rain and convective storm. The AMR distribution of a given storm type can be derived from the corresponded event occurrence distribution and event rainfall distribution, and the AMR distribution of all events is a mixture distribution of different types of AMR distribution. As a result, the EMS method provides a more suitable and effective design-rainfall than the traditional approach. The EMS method outperforms the AMS approach in many ways. In Monte Carlo simulation, the EMS method is superior to AMS method in terms of the bias and Root Mean Squared Error (RMSE). Three stations in Taiwan are selected for frequency analysis and peak flow analysis, the results show that EMS method can avoid overestimation, capture larger peak flow events and is less affected by outliers. Finally, simulation and real data analyses of confidence interval (CI) through bootstrap method are performed. Although CI of both method does not achieve the theoretical coverage rate, the coverage rate of EMS method is more stable in different return period.
39
"Changes in rainfall characteristics and reflectivity-rainfall rate relationships in Hong Kong". 2011. http://library.cuhk.edu.hk/record=b5894868.
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Lau, Stephen Po Wing."August 2011."
Thesis (M.Phil.)--Chinese University of Hong Kong, 2011.
Includes bibliographical references (leaves 62-66).
Abstracts in English and Chinese.
List of figures --- p.vi
List of tables --- p.ix
Chapter Chapter 1: --- Background --- p.1
Chapter Chapter 2: --- Changes in Rainfall Characteristics in Hong Kong --- p.3
Chapter 2.1 --- Introduction --- p.3
Chapter 2.2 --- Data --- p.5
Chapter 2.3 --- Method --- p.6
Chapter 2.3.1 --- Linear Regression Analysis --- p.8
Chapter 2.3.2 --- Empirical Mode Decomposition --- p.9
Chapter 2.4 --- Result --- p.12
Chapter 2.4.1 --- Rainfall Rate Categories --- p.12
Chapter 2.4.2 --- Rainfall Events Statistics --- p.20
Chapter 2.4.3 --- Diurnal Variation --- p.26
Chapter 2.4.4 --- Rainfall Rate Distribution --- p.30
Chapter Chapter 3: --- Reflectivity-rainfall Rate Relationships in Hong Kong --- p.33
Chapter 3.1 --- Introduction --- p.33
Chapter 3.2 --- Data --- p.35
Chapter 3.3 --- Method --- p.37
Chapter 3.3.1 --- Linear Regression Analysis --- p.37
Chapter 3.4 --- Result --- p.38
Chapter 3.4.1 --- Comparison of Rainfall Rate from Various Sources --- p.39
Chapter 3.4.2 --- Raindrop Size Distributions under Various Classification Schemes --- p.42
Chapter 3.4.3 --- Z-R Relationships Derived from Various Sources --- p.48
Chapter Chapter 4: --- Conclusion --- p.58
Bibliography --- p.62
40
Mkhize, Nhlakanipho. "Quantifying monthly areal rainfall uncertainty using a data-based stochastic rainfall generator". Thesis, 2015. http://hdl.handle.net/10539/17552.
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This study aims to establish whether a data-based model of incorporating uncertainty in daily
areal rainfall estimates can be adapted to a coarser monthly time scale and still provide
reasonable uncertainty estimates for water resource modelling applications. The daily
generator was formulated as a simple, efficient and robust model of stochastically generating
sequences of uncertainty-impacted areal rainfall estimates from point rainfall measurements.
The data - based model is tested on 8 catchments spread across South Africa. It is found
that the selected rain gauge combinations have an impact on one of the parameters of the
model (the scaling factor) and the degree of bias on the standard deviation and skewness
values of the generated stochastic sequences. A correlation-based rain gauge selection
approach is proposed to minimise this bias.
Statistical analysis of the generated stochastic areal rainfalls shows that the data-based
model provides realistic uncertainty estimates. However the actual bias on the low rainfalls
(< 20th percentile) is between 0.9 – 46.8%. The importance of these rainfalls in water
resource modelling applications though is low.
41
Chu, Chun-Kuang, i 屈峻廣. "Temporal and Spatial Variations of Rainfall and Rainfall Erosivity in Southern Taiwan". Thesis, 2014. http://ndltd.ncl.edu.tw/handle/cj5655.
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碩士國立屏東科技大學
水土保持系所
102
In recently years, trend of the rainfall characteristics have gradually changed due to extremely heavy rainfall event in the world. Rainfall is the major cause of soil erosion dynamic factor. Rainfall erosivity is a numerical description of the potential of rainfall to erode soil and is one of the key input parameter for USLE modeling. The purpose of the present study is estimating the rainfall erosivity based on event, monthly, seasonal, dry and wet seasonal and annual precipitation data, respectively. Temporal and spatial variations of rainfall and rainfall erosivity are investigated using a dataset monitored by 76 rainfall stations (from 1993 to 2012) in southern Taiwan. There are 70% of all rainfall erosivity stations that the individual maximum rainfall amount and kinetic energy erosivity occurred during typhoon Morakot, 2009. We found that the rainfall and the rainfall erosivity have a strong positive relationship (R2> 0.7). The maximum annual rainfall erosivity varied from 31,062 to 144,248 MJ-mm/ha-hr-yr. Most of the average monthly rainfall and rainfall erosivity happened from May to October (above 90% of the yearly ones). The average maximum monthly rainfall was 566 mm on the June or August, and the average maximum monthly rainfall erosivity is 9,386 MJ-mm/ha-hr on the August. Most of the seasonal rainfall and rainfall erosivity happened in summer or fall (more than 90% of the yearly ones). More than 90% of the yearly rainfall and rainfall erosivity happened in the wet seasonal. The average yearly rainfall and rainfall erosivity are 2,243 mm and 32,080 MJ-mm/ha-hr-yr, respectively. The rainfall erosivity values in southern Taiwan are higher than other world’s ones. It shows that there is a serious rainfall erosion problem in the study area. Result of temporal variation shows that the average monthly, seasonal and yearly rainfall and rainfall erosivity increase year by year. The spatial analysis shows the average yearly rainfall and rainfall erosivity increase from western region to eastern region and from plain to mountain region. The relationship of average yearly rainfall, rainfall erosivity and elevation show that the average yearly rainfall amount and rainfall erosivity abruptly increase as the elevation (< 1,000 m) increase, but they decrease as the elevation (> 1,000 m) increase.
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SIE, JIA-SHEN, i 謝佳燊. "Development and application of hourly rainfall generator for short-duration rainfall event". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/m7t7a8.
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碩士逢甲大學
水利工程與資源保育學系
105
Rainfall generators are usually developed to generate daily rainfall data that are not well suited for studies of severe rainfall-induced disasters. This study developed an hourly rainfall generator for generating short-duration rainfall events. Hourly rainfall data from three meteorological stations in Taiwan were used as the case study. Statistical analysis was preformed to obtain the parameters of the short-duration rainfall events, and those parameters were used by the generator to reproduce hourly rainfall data. Comparative results indicate that the proposed hourly rainfall generator can reproduce rainfall data with similar values of the average and standard deviation. In addition, this study used the hourly rainfall generator to generate short-duration rainfall events under the scenario of increased urban temperature in Taichung, with the established statistical relationship between the increased urban temperature and the change rate of rainfall parameters in Taichung. Scenario data indicate an increased amount and diversity of short-duration rainfall events in the wet season.
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Wei-Ze, Liou, i 劉維則. "Temporal and Spatial Variations of Rainfall and Rainfall Erosivity in Eastern Taiwan". Thesis, 2014. http://ndltd.ncl.edu.tw/handle/28389074657954001090.
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碩士國立屏東科技大學
水土保持系所
102
In recently years, frequency of high intensity rainfall, long rainfall duration and heavy rainfall are found to increase in Taiwan (Chen, 2008). Rainfall erosivity index R is a key input parameter to the USLE. R describes the soil loss potential caused by precipitation, which can be understood to change in correspondence to changes in extreme rainfall events. R is calculated from the total kinetic energy and the maximum 30-min rainfall intensity of a storm. Therefore, a lack of short duration rainfall intensity data in some countries makes applying the rainfall erosivity index more difficult. For those areas without the data and resources required to calculate rainfall erosivity index, an alternative approach has typically been used to estimate rainfall erosivity index. The purpose of the present study is estimating the rainfall erosivity based on event, monthly, seasonal, dry and wet seasonal and annual precipitation data, respectively. Temporal and spatial of rainfall and rainfall erosivity variations are investigated using 19,106 effective rainfall events by 51 rainfall stations of the Central Weather Bureau (from 1993 to 2012) in eastern Taiwan (Yilan, Hualien, Taitung). The result shows that maximum annual rainfall erosivity varied from 12,217 to 173,529 MJ-mm/ha-hr-yr. Rainfall and rainfall erosivity have a strong positive relationship. Temporal variation of rainfall erosivity shows that the average monthly, seasonal and yearly rainfall and rainfall erosivity increase year by year. The spatial analysis shows average annual rainfall erosivity increases from plain to mountain region, and from southern to northern (from Taitung to Yilan). Average annual rainfall erosivity is highly related with the latitude. In addition, rainfall erosivity index is affected by the typhoon and the northeast monsoon in eastern Taiwan.
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Wang, Chieh-Yu, i 王婕妤. "Regional Changing Patterns of Total Rainfall, Extreme Rainfall and Drought in Taiwan". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/92160467427782734086.
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碩士國立中央大學
土木工程研究所
100
In the recent years, the rainfall intensity rises sharply in Taiwan due to global climate variations, and it may result in the situations such as increased flooding and droughts, the reservoir storage volume is insufficient, and it causes the management and the distribution of water resources more and more difficult in the future. This study discussed the influence of floods and drought under climate change, and analyzed rainfall by the Mann-Kendall method for the trends in year 1961-1990 and that in 1991-2010. First, this study analyzed 50 years long-term rainfall data to discuss the change of trend, and to calculate the total rainfall and the rainfall patterns in spatial. Second, this study analyzed the return period of the single day maximum rainfall and the maximum continuance days without rainfall by frequency analysis in year 1961-1990 and 1991-2010. Last, this study discussed the effect of the extreme rainfall and the drought under climate change in Taiwan. According to the analysis result of Mann-Kendall method, there was an obvious trend appeared in the alternate drying and wetting month. The average annual rainfall showed an increasing trend in both central and southern Taiwan. Analyzing average annual rainfall and average amount of water by the Kriging method, the rainfall patterns had changed in spatial in northern Taiwan. The average annual rainfall decreased between the elevation of 200 meter above sea and that of 1000 meter above sea, and the average annual rainfall increased for the elevation above 1000 meter. In central and southern Taiwan, the average annual rainfall increased for region above the elevation of reservoir sites. In addition, the frequency analysis result showed that the rainfall intensity increased sharply in the central and south area under climate change. Extreme rainfall had changed the return period, i.e., more sever rainfall is expected in 1991-2010 than that in 1961-1990. In Central and Southern Taiwan, the range of small-scale and large-scale drought would spread gradually to inland in 1991-2010. During this period, the probability of large-scale drought occurring is 0.02 in the central and south area along the coast, while the probability is less than 0.01 in Northern Taiwan.
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Chen, Chih-Hao, i 陳志豪. "Temporal and Spatial Variations of Rainfall and Rainfall Erosivity in Central Taiwan". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/d8hj6p.
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碩士國立屏東科技大學
水土保持系所
105
The Universal Soil Loss Equation (abbreviated as USLE) is presently one of the most widely used models to evaluate soil erosion. Along with the impact by climate change, it is not certain that the rainfall erosivity index can reflect the variations at present and in the future. Rainfall erosivity index (R30) shows the potential ability of the soil loss caused by precipitation and runoff for predicting soil loss from agricultural hillslopes. Wischmeier and Smith (1958) defined R30 as the average of the annual summations of storm EI30 values, excluding storms with a total rainfall depth of less than 12.7 mm. The E portion of this value represents the rainfall energy, and the I30 portion represents the maximum 30-min rainfall intensity during the storm. In this study, central Taiwan was used as the research site. By using 10-min rainfall data of 105 precipitation stations of the period between 2002 and 2015, we conducted regression analysis and temporal-spatial variations to discuss the relationship between monthly, seasonal, and annual precipitation and the rainfall erosivity index of the study area. A geographic information system was employed to plot the average annual precipitation and rainfall erosivity index isogram of central Taiwan. The result shows that the regression formulas between precipitation and rainfall erosivity index based on 49,583 effective rainfall events from 2002 to 2015 have highly correlations. The values of average monthly precipitation and rainfall erosivity index approached to 85% of the year from May to October. The maximum of average monthly rainfall and rainfall erosivity index were 455 mm in August and 6,243 MJ-mm/ha-hr in July, respectively. The average seasonal precipitation and rainfall erosivity index concentrated on summer and autumn. The average annual precipitation and rainfall erosivity index ranged between 756 to 4,552 mm and 5,679 to 82,445 MJ-mm/ha-hr-yr, respectively. In comparison with other tropical countries, the study area is a severe soil-loss region of the world. The temporal and spatial variations of precipitation and rainfall erosivity index are also analysis in this study. The results show that the temporal variations of annual precipitation and rainfall erosivity have been trending up from 1993 to 2015. The spatial variations of precipitation and rainfall erosivity index are increasing from plain to mountain area.
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Liao, Yi-Wen, i 廖怡雯. "Estimation of Rainfall Erosivity Index Using Hourly Rainfall Data in Northern Taiwan". Thesis, 2018. http://ndltd.ncl.edu.tw/handle/ev3f3r.
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碩士國立屏東科技大學
水土保持系所
106
In recent years, due to the improper development of slopeland, the soil erosion is increasingly serious. In order to effectively use water and soil resources perpetually, assessment of soil erosion is an important issue. The Universal Soil Loss Equation (USLE) is presently one of the most widely models to evaluate soil erosion. The Rainfall erosivity index (R30) in the USLE is calculated from the total kinetic energy and the maximum 30-min rainfall intensity of a storm. R30 values are calculated from rainfall information obtained from continuous recording. However, detailed chart-recorded rainfall data are not readily available, whereas hourly rainfall is available in many places. This study sets up in a simple method for estimating the rainfall erosivity index (R30) by using the value of R60 calculated from the rainfall kinetic energy (E60) and maximum intensity (I60max) measured at multiple rainfall stations. The data set consists of 29,659 storm events monitored by 61 rainfall stations located in northern Taiwan. It is shown that the average conversion factors (αE, αI, αRj and αRy) of the rainfall kinetic energy (E), the rainfall intensity (I), the rainfall erosivity index (Rj) and annual rainfall erosivity index (Ry) (i.e., the ratios of the 10-min to 60-min interval values of the corresponding factors) are respectively 1.057, 1.504, 1.350 and 1.497. The variations of average conversion factors (αE, αI, αRj and αRy) have a slight decrease with elevation. This study suggests that if the selections of rainfall stations have similar rainfall characteristics and locate around adjacent areas, the variation trend between average conversion factors and elevation may be more noticeably.
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Ling-Chia, Chang, i 張凌嘉. "Study of Rainfall Option". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/78774715662606924469.
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碩士東吳大學
國際經營與貿易學系
101
In recent years, global climate anomalies began to appear in many parts of the world also caused extreme climate. Taiwan is surrounded by sea, which affected by the weather is very wide. In this study, we use the rainfall factor as explored. In real options perspective, through simulated rainfall amounts converted to become the budget so that rainfall is becoming a real asset and the government as the purchaser. In order to build a climate of rainfall as a factor of derivatives - options rainfall, heavy rain caused agricultural risk aversion, available to policy makers a reference. In this study, distribution of rainfall in Taiwan is divided into northern, central, southern and eastern four blocks. According to recent literature approaches used to estimate rainfall distribution - Gamma distribution and Weibull distribution combined with historical rainfall provided by Taiwan's Central Weather Bureau. It will both be fit and to elect suitable rainfall distribution in each region. After estimated parameters and calculate the value of European call for the preparation of the government budget.
48
Rosenberg, Kathrine Joan. "Stochastic modelling of rainfall and generation of synthetic rainfall data at Mawson Lakes". 2004. http://arrow.unisa.edu.au:8081/1959.8/24949.
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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.
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Chang, Chan-Hua, i 張展華. "Characteristics of Annual rainfall and Maximum one day rainfall in Kao-Ping Area". Thesis, 2003. http://ndltd.ncl.edu.tw/handle/58162691719786829098.
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碩士國立屏東科技大學
水土保持系
91
Five frequency analysis methods were used in this study for the Maximum one day rainfall and annual from the data issued by Central Weather Bureau(CWB) of weather observation station in December, 2000(5th edition) and data in annual book about 188 weather observation stations of CWB in Kaohsiung and Pingtung. As the results of analysis shown, it is suggested to use Pearson type Ⅲ method for predicting frequency analysis of annual rainfall in Kaohsiung City, Kaohsiung County, Pingtung County, and the whole region of Kaohsiung and Pingtung; for the Maximum one day rainfall,Log Natural Distribution for predicting frequency analysis is suggested to use in Kaohsiung City, Log Pearson type Ⅲ method in Kaohsiung County, Pingtung County, and the whole region of Kaohsiung and Pingtung. Based on the distributions from applicable theories, the most applicable theory for each station was found. Then, use the hydrological frequency analysis to estimate the hydrological parameters of 5-yr, 20-yr, 25-yr, 50-yr and 100-yr, and draw the rainfall contour map accordingly for the reference for different requirements. The rainfall contour map shows that the rainfall increases as the elevation increases, but it is hard to estimate the increase rate. By taking each village, town, city and district as the regional units, the frequency regression equations, R squares and standard deviations were obtained, which can provide the relevant engineers an easy way to obtain the hydrological parameters for the reference of construction design. As for the relationship of rainfalls and elevations of station, it can be found from the results of this study that the more the year number of record, the closer the relationship between the average annual rainfall and the maximum one day rainfall. Therefore, as the year number of record increases, the reliability of the hydrological frequency analysis increases. However, the average annual rainfall and the maximum one day rainfall increase as the elevation of the stations increases, but there is no fixed increase trend. The average annual rainfall and maximum one day rainfall have no conspicuous relationship with the elevations of the stations. Especially, the relationship of the maximum one day rainfall and the elevation is worse.
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Chuang, Chun-Wan, i 莊純宛. "Temporal and Spatial Variations of Rainfall Amounts and Rainfall Erosivity in Northern Taiwan". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/yu2p9b.
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碩士國立屏東科技大學
水土保持系所
105
The Universal Soil Loss Equation (USLE) is presently one of the most widely used models to evaluate soil erosion. The present study proposes four regression models for estimating the erosivity factor based on event, monthly, seasonal and annual precipitation data, respectively. The data set consisted of 29864 storm events for the period 1993 to 2015, monitored by 61 rainfall stations of the Central Weather Bureau (CWB) in Northern Taiwan, was used to analyze the temporal-spatial variations of rainfall erosivity. The result shows that the maximum annual rainfall erosivity varied from 18,434 to 216,507 MJ-mm ha-1 hr-1 yr-1. The average of monthly rainfall (Pm) and monthly rainfall erosivity (Rm) concentrated in May to November, most of the seasonal rainfall (Ps) and the seasonal rainfall erosivity (Rs) happened in wet season. The average of yearly rainfall (Py) is 2,333 mm and the yearly rainfall erosivity (Ry) is 20,493 MJ mm ha-1hr-1yr-1. There is an obvious rainfall erosion problem in the area due to the rainfall concentration. Most of the temporal variations for rainfall and rainfall erosivity based on average monthly, seasonal and annual precipitation data increased year by year. The spatial variations of precipitation and rainfall erosivity index have increasing trends from plain to mountain area. The variations of rainfall erosivity index between this study and Huang’s (1979) were discussed. It was found that the average annual rainfall erosivity index had an increasing trend over the past few decades.