Mémoire (M.Sc.A.)-- Université du Québec à Chicoutimi, 1991. / Bibliogr.: f. 86-91. Document électronique également accessible en format PDF. CaQCU

Thesis (M.S.)--University of Missouri-Columbia, 2008. / 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 August 13, 2009) Includes bibliographical references.

Thesis (Ph.D. (Institute for Water Research)) - Rhodes University, 2009.

Thesis supervisor: Witold F. Krajewski. Includes bibliographic references (p. 187-202).

Thesis (M. Sc. (Institute for Water Research))--Rhodes University, 2005.

Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2009. / Full text also available online. Scroll down for electronic link.

Thesis (M. S.)--Florida State University, 2006. / Advisor: James J. O'Brien, Florida State University, College of Arts and Sciences, Dept. of Meteorology. Title and description from dissertation home page (viewed Sept. 21, 2006). Document formatted into pages; contains ix, 40 pages. Includes bibliographical references.

Hydrological variability involving rainfall and streamflows in southern Africa have been often studied separately or have used cumulative rainfall and streamflow indices. The main objective of this study was to investigate spatio-temporal variations of rainfall, their influences on streamflows and their relationships with climatic variations with emphasis on indices that characterise the hydrological extremes, floods and droughts. It was found that 60-70% of the time when it rains, daily rainfalls are below their long-term averages and daily amounts below 10 mm are the most frequent in southern Africa. Spatially, climatologies of rainfall sub-divided the southern African subcontinent into the dry western/southwestern part and the “humid” eastern and northern part. The daily amounts below 20 mm contribute significantly to annual rainfall amounts in the dry part while all types of daily rainfall exceeding 1 mm have comparable contributions in the humid part. The climatologies indicated the highest likelihood of experiencing intense daily events during the core of the wet seasons with the highest frequencies in central Mozambique and the southern highlands of Tanzania. Interannual variations of rainfall indicated that significant changes had occurred between the late-1940s and early-1980s, particularly in the 1970s. The changes in rainfall were more evident in the number of daily rainfall events than in rainfall amounts, led generally to increasing early summer and decreased late summer rainfall. It was also found that intra-seasonal dry day sequences were an important parameter in the definition of a rainy season’s onset and end in southern Africa apart from rainfall amounts. Interannual variations of the rainy season characteristics (onset, end, duration) followed the variations of rainfall amounts and number of events. The duration of the rainy season was affected by the onset (Tanzania), onset or end (tropical southern Africa - southwestern highlands of Tanzania, Zambia, northern Zimbabwe and central Mozambique) and end (the remaing part of southern Africa). Flow duration curves (FDCs) identified three types of rivers (ephemeral, seasonal and perennial) in southern Africa with ephemeral rivers found mainly in the dry western part of the region. Seasonal streamflow patterns followed those of rainfall while interannual streamflow variations indicated significant changes of mean flows with little evidences of high and low flow regime changes except in Namibia and some parts of northern Zimbabwe. It was, however, not possible to provide strong links between the identified changes in streamflows and those in rainfall. Regarding the influences of climate variability on hydrological variability in southern Africa, rainfall variations in southern Africa were found to be influenced strongly by ENSO and SST in the tropical Indian ocean and moderately by SST in the south Madagascar basin. The influence of ENSO was consistent for all types of daily rainfall and peaks for the light and moderate (< 20 mm) events in the southern part and for the intense events in the northern part. SST in the tropical Indian ocean influence the light and moderate events while SST close to the region influence the heavy events. However, the relationships experienced significant changes in the mid-1950s and in the 1970s. The former changes led to improved associations while the latter deteriorated or reversed the relationships. The influences of climatic variables on streamflows and rainy season characteristics were inferred from the rainfall-streamflow and rainfall-climatic variables relationships.

Text in Afrikaans, abstract in Afrikaans and English / As deel van die weermodifikasie-eksperiment in Bethlehem, Suid-Afiika, is 'n reenmeternetwerk geinstalleer, en word die neerslagwaardes R; wat by 43 reenmeterstasies waargeneem is, vergelyk met die waargenome radar reflektiwiteit Z;. Alhoewel radar ruimtelike en tydskontinue metings van reflektiwiteit bied wat onmiddellik by een sentrale punt beskikbaar is, is die akkuraatheid van radar om reenval te meet onseker as gevolg van verskeie potensiele foute in die omskakeling van reflektiwiteit na reenval. Dit word aanvaar dat reenmeters akkurate puntwaarnemings van reenval gee en daar bestaan eenstemmigheid dat die kombinasie van die twee metodes beter is as enigeen van die metodes afsonderlik. In hierdie studie ondersoek ek die toepassing van die veralgemeende lineere model as 'n beramingstegniek. Vorige studies gebruik die log-log transformasie, d. w.s. logZ = logA + b(logR) van die Z = ARb verwantskap om die koeffisiente A en b met behulp van kleinste-kwadrate-regressie te bepaal. Die implisiete aanname hiermee is dat die foute ongekorreleerd is. Met die inverse verwantskap R = czd d.w.s. logR = logC + d(logZ) neem ek aan dat die waarnemings nie onafhanklik is nie sodat die regressiekoeffisiente bereken word met behulp van die metode van die veralgemeende lineere model. Om die ruimtelike afhanklikheid van die reenmeterwaarnemings te modelleer, word eksperimentele variogramme uit die data bereken en gepas met teoretiese variogramme wat gebruik word om die variansie-kovariansiematriks te vu!. "Gemiddeld" vaar hierdie metode beter as gewone regressie vir analises wat reenmeters wat verder as 45km vanaf die radarstel is, insluit. Residu-stipping wys dat die afstand van die meter vanaf die radarstel as 'n afsonderlike onafhanklike veranderlike in die regressievergelyking ingesluit behoort te word, d.w.s. die beraming verbeter met logR = 3-0 + a,(logZ) + a2(afstand). Hierdie meervoudige regressiemodel stem ooreen met die teoretiese model van Smith en Krajewski omdat e -- afstand as 'n praktiese manifestasie van die foutproses [e.,, (ij)] beskou kan word. Omdat E(ez) = eE<ZJ e'"a' as Z 'n lognormaalverdeling het, kan die sydigheid wat ontstaan wanneer antilogaritmes geneem word, reggestel word deur die beraamde reenval met e112 "' te vermenigvuldig. Die studie !ewer 'n bydrae met die afleiding van 'n beramingstegniek wat die beraming van neerslag uit radar betekenisvol verbeter. / In a study of a rain-gauge network that was installed for a weather modification experiment in Bethlehem, South Africa, precipitation values R; observed at 43 gauging stations are compared to the observed radar reflectivity Z;. Although radar provides spatial and temporal measurements of reflectivity that are immediately available at one location, the accuracy of radar estimation of rainfall is uncertain due to various potential errors in the conversion from reflectivity to rainfall. Rain-gauges are assumed to give accurate point measurements of rainfall and there is general agreement that the combination of systems is better than either system alone. In this study I explore the application of the general linear model as an estimation technique. Previous studies have used the log-log transform, i.e. logZ = logA + b(logR) of the Z = ARb relation, and applied least-squares regression analysis to determine the coefficients A and b. This implicitly assumes that the disturbances are uncorrelated. Working with the inverse relation R = czd i.e. logR = logC + d(logZ) and assuming that the observations are not independent we compute the regression coefficients using generalised least squares. To model the spatial dependence of the rain-gauge observations we compute experimental variograms from the data and fit them with theoretical variograms which are then used to fill the variance-covariance matrix. "On average" this method performs better than ordinary regression for the analyses that included rain-gauges further than 45km from the radar set. Residual plotting revealed that distance of the rain-gauge from the radar set should be included as a separate independent variable in the regression equation, i.e. logR = ao + a1(logZ) + a1(distance) improved the estimation of rainfall as it performs better than ordinary regression. This multiple regression model agrees with the theoretical model of Smith and Krajewski in the sense that e "'distance is a practical manifestation of the error process [ e,, (ij)]. Showing that E( ez) = el!.(!.) e 112 "' if Z has a lognormal distribution, the bias when taking antilogs can be removed by multiplying estimated rainfall by e1 ' 2a'. The contribution of this study is the derivation of an estimation technique which significantly improves the estimation of rainfall from radar / Mathematical Sciences / D. Phil. (Statistics)

Made available in DSpace on 2014-06-11T19:24:43Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-08-24Bitstream added on 2014-06-13T20:32:03Z : No. of bitstreams: 1 antonio_caa_me_botfca.pdf: 2765325 bytes, checksum: 280098279ffdbea961a48e5dc795f5a5 (MD5) / As medidas diárias de chuva acumulada são informações de suma importância para a agricultura como, por exemplo, na aplicação de insumos, na estimativa da irrigação ou em cálculos de balanços hídricos. As informações atualmente disponíveis sobre chuvas diárias são, no geral, provenientes de pluviômetros convencionais de operação manual. A eficiência de pluviômetros em mensurar a precipitação em uma área está diretamente relacionada à distância entre os equipamentos. A maior rede de pluviômetros em operação no Estado de São Paulo, que está sob responsabilidade do DAEE (Departamento de Águas e Energia Elétrica), disponibiliza os totais diários com vários meses de defasagem, impossibilitando a utilização imediata dessas informações. A utilização de radares meteorológicos para a quantificação de chuva está associada à eficiência de equações de conversão do sinal eletrônico do radar (Z) em chuva (R), denominada relação ZR. Utilizando dados pluviométricos diários, entre 1995 e 1999, de sete estações dispostas numa área de 1.500 km2, e comparando com dados de radar no mesmo período, foi possível estabelecer uma relação ZR probabilística visando à acumulação diária da precipitação, representativa a área delimitada. A aplicação da relação ZR ajustada à área delimitada resultou em acumulações diárias mais próximas dos resultados observados pelos dados dos pluviômetros, quando comparadas aos resultados da relação ZR atualmente em uso, nos radares da UNESP. Nas acumulações de chuva, obtidas por radar, foram aplicadas interpolações geoestatísticas, resultando na melhoria da distribuição espacial dessas acumulações. Objetivando a complementação espacial e temporal das informações de chuva acumulada atualmente disponíveis, este estudo demonstra uma metodologia apropriada para determinação... / The daily measures of accumulated rain are very important information for agriculture, for example, in the fertilezer applications, the estimate of the irrigation or calculation of water balance. Currently, the information available of daily rain is, generally, provenient form conventional rain gauges manually operated. The efficiency of rain gauges in measuring the precipitation in an area is directly related to the distance between equipment. The biggest rain gauges net operating in the State of São Paulo in under responsibility of DAEE (Department of Water and Electric Energy) which provides daily information with several months of delay, impeding the information to be used immediately. The use of meteorological radars for the quantification of rain is associated to the efficiency of conversion equations of the radar electronic sign (Z) in rain (R), known as relationship ZR. Using daily rain data between 1995 and 1999, from seven stations located in an area of 1,500 km2 and comparing whit data from the radar in the same period, it was possible do establish a ZR probabilistic relation aiming at the daily amount of precipitation, which represents the delimited area. The application of the ZR relationship adjusted to the delimited area resulted in daily accumulation closer to the results observed by the rain gauges data when compared to the results of the ZR relationship currently in use in radar operated by UNESP. In the accumulation of rain, taken by the radar, geostatistic interpolations were applied, and the results were a better spatial distribution of these accumulations. Objectifying the space and temporal complementation of currently available the accumulated rain information, this research demonstrates an appropriate methodology to determinate regional ZR relationship, based on data from rain gauges, and the application of geoestaistic interpolation... (Complete abstract click electronic access below)