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Rainfall: measurements, variability and laboratory simulations

Carvalho, Sílvia
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Tese de Doutorado
ENG
Relevância na Pesquisa
37.12%
A caracterização da pluviosidade assume uma importância fundamental em diversos domínios da hidrologia e em aplicações de engenharia, como por exemplo na modelação do escoamento, da erosão dos solos, e do clima, na calibração de dados de deteção remota, na conceção de sistemas de captação de água da chuva, entre outros. O trabalho apresentado nesta tese foca alguns aspetos relacionados com a pluviosidade, dando especial atenção à medição e caracterização da variabilidade da pluviosidade, tanto à escala do evento como em séries temporais históricas. A caracterização das propriedades das gotas de chuva (tamanho e velocidades de queda) é também destacada neste trabalho tanto sob condições naturais como laboratoriais, sendo particularmente importante para estudos de erosão hídrica. A primeira parte da tese foca-se na pluviosidade natural. O conjunto de dados usados inclui: (i) séries temporais anuais e mensais que datam do século XIX, obtidas por estações meteorológicas dispersas por Portugal; (ii) mais de 3 anos de medições obtidas numa instalação experimental localizada em Coimbra, usando diferentes tipos de pluviómetros, incluindo um distrómetro que regista dados com resolução de 1 minuto. As séries temporais longas permitiram o estudo de tendências monotónicas e parciais na pluviosidade mensal e anual; enquanto que os dados com elevada resolução temporal foram usadas para caracterizar os eventos pluviosos de acordo...

Extremos de precipitação diária em Belém, Pará, e estrutura vertical da atmosfera; Extreme daily rainfall in Belém, Pará, and vertical structure of atmosphere

Camponogara, Glauber
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 06/03/2012 PT
Relevância na Pesquisa
37.06%
Diversas atividades ligados ao gerenciamento de recursos hídricos necessitam da previsão de acumulados diários de chuva extremos. Entretanto, grande parte dos modelos utilizados operacionalmente apresentam uma tendência a subestimar os extremos de precipitação mesmo com apenas 24 horas de antecedência. Existem diversas razões para esse tipo de erro de previsão tais como, limitações nas parametrizações de convecção para modelos com resolução de dezenas de quilômetros e a não inclusão do efeito de aerossóis como núcleos de condensação de gotas de nuvens nos modelos de grande escala. Dentro desse contexto, este trabalho tem como objetivo analisar situações de eventos extremos de precipitação na região de Belém, Pará, onde o regime de precipitação é modulado, principalmente, pela brisa marítima, linhas de instabilidade, distúrbios ondulatório de leste, zona de convergência intertropical, alta da Bolívia e Vórtices Ciclônicos de Altos Níveis (VCAN). A abordagem será de identificação de perfis verticais cinemáticos e termodinâmicos típicos de eventos extremos de precipitação diária em Belém, Pará. Para esse fim, escolheu-se fazer uma análise de dados de radiossondagem e precipitação utilizando as Funções Ortogonais Empíricas (EOF - Empirical Orthogonal Functions combinadas e verificar como o Brazilian developments on the Regional Atmospheric Modeling System (BRAMS) simula características básicas de chuva acumulada diária. A variância explicada das EOF calculadas a partir do conjunto de variáveis acumulado diário de precipitação (acpcp)...

Dinâmica da formação de crostas superficiais em função de práticas de preparo do solo e chuva simulada; Dynamic of surface crust formation in different tillage systems and simulated rainfall

Rosa, Jaqueline Dalla
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 10/07/2012 PT
Relevância na Pesquisa
37.02%
As crostas são o resultado da degradação da estrutura superficial dos solos, favorecem a erosão e a degradação ambiental dos solos. Este estudo avaloiu a dinâmica da formação de crostas superficiais e as consequencias sobre a porosidade, condutividade hidráulica (K), retenção de água, densidade (Ds) e a rugosidade de um Argissolo Vermelho amarelo conduzido com diferentes sistemas de preparo do solo e aplicação de lâminas de chuva simulada. Avaliou-se também, através de um experimento em laboratório, os processos envolvidos na quebra dos agregados, sob chuvas simuladas. O experimento foi conduzido, nos anos de 2009 e 2010. Em parcelas de 15 x 30 m foram conduzidos os diferentes preparos do solo: preparo convencional (PC), preparo reduzido (PR) e sem preparo (SP). Dentro das parcelas instalou-se micro-parcelas de 1m x 1m, onde foram aplicadas diferentes lâminas de chuva simulada (0, 27, 54 e 80 mm) com intensidade de 80 mm h-1. Foram realizadas coletas de dados de rugosidade, medidas de K, coleta de amostras indeformadas de solo para análise da porosidade e confecção de lâminas delgadas, e também anéis cilíndricos para curva de retenção de água (CRA) e Ds do solo. No experimento de laboratório, utilizou-se dois solos (siltoso e argiloso) e duas classe de agregados (1-3 e 3-5 mm). Os agregados foram submetidos a diferentes chuvas simuladas (28mmh-1 + EC forte; 28mmh-1 + EC fraca; 90mmh-1 + EC forte; 90mmh-1 + EC fraca) e após avaliou-se o diâmetro médio ponderado dos agregados (DMP). A dinâmica da formação de crostas ocorreu de maneira diferenciada em ambos os sistemas de preparo. Nos sistemas de PC e PR a maior redução da porosidade...

Erosividade, coeficiente de chuva, padrões e período de retorno das chuvas de Quaraí, RS; Erosivity, rainfall coefficient and patterns and return period in Quarai, RS, Brazil

Bazzano, Marcos Gabriel Penãlva; Eltz, Flavio Luiz Foletto; Cassol, Elemar Antonino
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Artigo de Revista Científica Formato: application/pdf
POR
Relevância na Pesquisa
37.12%
O conhecimento da potencialidade das chuvas em causar erosão é necessário para planejamento de atividades agrícolas e de engenharia civil. Para a localidade de Quaraí (RS), foram determinados a erosividade da chuva e a relação com a precipitação e o coeficiente de chuva, os padrões hidrológicos e o período de retorno das chuvas. Utilizaram-se dados pluviográficos diários do período 1966-2003. Para cada chuva erosiva, foram separados os segmentos do pluviograma com a mesma intensidade e registrados os dados em planilha. Com o programa Chuveros, foram calculadas as erosividades mensal, anual e média das chuvas pelo índice EI30, no Sistema Internacional de Unidades, e os padrões hidrológicos de chuva, bem como o coeficiente de chuva. Foram realizadas correlações de Pearson e regressões lineares simples entre o índice de erosividade EI30 e os valores médios mensais (p) e anuais (P) de precipitação e do coeficiente de chuva (Rc). Foi calculada a intensidade máxima da chuva pelo método da distribuição extrema tipo 1 para durações de chuva de 1/6, 1/3, 1/2, 1, 2, 4, 8, 12, 24 e 48 h e períodos de retorno da chuva de 2, 5, 10, 20, 50 e 100 anos. Foram ajustadas equações que relacionam a intensidade máxima e a duração da chuva para os períodos de retorno da chuva de 2...

A Variabilidade da precipita????o no Rio Grande do Sul e sua rela????o com o ??ndice de Oscila????o Ant??rtica; Variability of rainfall in Rio Grande do Sul and its relationship with the Antarctic Oscillation Index

GARCIA, Maria Arita Madruga
Fonte: Universidade Federal de Pelotas; Meteorologia; Programa de P??s-gradua????o em Meteorologia; UFPel; BR Publicador: Universidade Federal de Pelotas; Meteorologia; Programa de P??s-gradua????o em Meteorologia; UFPel; BR
Tipo: Dissertação Formato: application/pdf
POR
Relevância na Pesquisa
37.05%
This research aims to analyze the monthly variations of rainfall in Rio Grande do Sul (RS) relating to monthly changes in the average thickness of the troposphere (700mb) at the bottom of the Southern Hemisphere, which is centered in the region of Antarctica. Monthly anomalies of atmospheric thickness have been represented by principal oscillation pattern that is called the Arctic Oscillation Index. This study is important because RS has played an important role in national agricultural production, and the variable rainfall has been identified as a key role in the productivity of different regional cultures. During the study, monthly rainfall data from 32 meteorological stations in RS has been used, which has been correlated with the Arctic Oscillation Index. The Arctic Oscillation Index has been obtained directly from Climate Prediction Center and the study period has been from 1979 to 2008 and, the correlations between the monthly rainfalls have been tested considering the time lags of index 0, -1, -2, -3 months. The results of the climatology have showed that rainfall in these last three decades have presented patterns and distributed monthly throughout the year and lower values to the south and higher to the north and northwest. The largest temporal gradient in RS has occurred between the months of October and November...

Rainfall Variability, Occupational Choice, and Welfare in Rural Bangladesh

Bandyopadhyay, Sushenjit; Skoufias, Emmanuel
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
EN_US
Relevância na Pesquisa
37.06%
This study investigates the choice of occupational focus versus diversification between household members in rural Bangladesh as an autonomous and proactive adaptation strategy against ex ante local rainfall variability risks. The analysis combines nationally representative household level survey data with historical climate variability information at the Upazila level. The authors note that flood prone Upazilas may face reduced risks from local rainfall variability as compared with non-flood prone Upazilas. They find that two members of the same household are less likely to be self-employed in agriculture if they live in an area with high local rainfall variability. However, the occupational diversification strategy comes at a cost to households in terms of consumption welfare. The paper considers the effects of three policy actions, providing access to credit, safety net, and market. Access to market appears to be more effective in reducing the likelihood of costly within-household occupational diversification as an ex ante climate risk-reducing strategy as compared with access to credit and safety net.

Monsoon Babies : Rainfall Shocks and Child Nutrition in Nepal

Tiwari, Sailesh; Jacoby, Hanan G.; Skoufias, Emmanuel
Fonte: World Bank, Washington, DC Publicador: World Bank, Washington, DC
EN_US
Relevância na Pesquisa
37.02%
Do household consumption-smoothing strategies in poor countries entail significant long-run costs in terms of reduced human capital? This paper exploits the timing of monsoon rainfall shocks and the seasonal nature of agriculture to isolate income effects on early childhood anthropometric outcomes in rural Nepal and to provide evidence on the persistence of these effects into later childhood. Findings suggest that a 10 percent increase in rainfall from historic norms during the most recently completed monsoon leads to a 0.15 standard deviation increase in weight-for-age for children ages 0-36 months. This total impact consists of a negative "disease environment effect" of no more than 0.02 standard deviations and a positive "income effect" as high as 0.17 standard deviations. Consistent with this interpretation, excess monsoon rainfall also enhances child stature, but only if the monsoon rainfall shock is experienced in the second year of life. Moreover, this effect on child height is transitory, dissipating completely by age five.

A point rainfall model for risk-based design

Heneker, T.; Lambert, M.; Kuczera, G.
Fonte: Elsevier Science BV Publicador: Elsevier Science BV
Tipo: Artigo de Revista Científica
Publicado em //2001 EN
Relevância na Pesquisa
37.02%
The point rainfall model presented extends previous work on event-based rainfall models and overcomes some of their shortcomings. The model uses event-based data and can be calibrated using rainfall data substantially affected by missing or corrupted values. Particular attention was given to adequately simulating extreme storm rainfall events for use in hydrological risk assessment. The model is capable of simulating the inter-event time, storm duration, average event intensity and intra-event temporal characteristics. Conditioning of the average event rainfall intensity on rainfall duration and time of year is a feature of the model. Rainfall events are disaggregated using a conditional random walk on a dimensionless mass curve. Pluviograph data in 6 min increments from three Australian capital cities (Sydney, Brisbane and Melbourne) was used to calibrate the model parameters. It was found that the constrained random walk parameters were almost identical for the three cities. The model was tested using statistics not used in its calibration and the simulated intensity–frequency–duration extreme rainfall statistics compared very favorably with observed values. In addition, simulated aggregated statistics compared favorably with observed statistics from 30 min to monthly durations. The simulated annual rainfalls significantly underestimated the observed variability for Brisbane and Sydney...

Rainfall regime and optimal root distribution in the Australian perennial grass, Austrodanthonia caespitosa (Gaudich.)

Williamson, Grant James
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2008
Relevância na Pesquisa
37.09%
This study aimed to determine whether rainfall regime has driven differentiation in the Australian perennial grass, Austrodanthonia caespitosa, resulting in local ecotypes possessing characters, such as deep rootedness or summer activity, that may be particularly useful in reducing deep drainage for salinity mitigation, or whether the species shows a plastic response in root growth to soil water distribution. Rainfall regime varies within a given annual rainfall because size and ditribution of rainfall event vary. This can have an important effect on soil water distribution, both spatially and temporally. This study investigates the relationship between rainfall regime and the structure of root systems in local populations of Austrodanthonia caespitosa (Gaudich.), Firstly, it examined a number of indices useful in quantifying variation in small-scale rainfall regime, including seasonal bias, event size, event frequency, and the clustering of events, as well as how rainfall event size may be changing over time across Australia. The variation in soil water distribution that results from different rainfall regimes is expected to interact with root distribution in plants, either acting as a selective force and driving genotypic differentiation in response to soil water availability...

Sensitivity of drainage to rainfall, vegetation and soil characteristics

Bah, A.; Kravchuk, O.; Kirchhof, G.
Fonte: Elsevier Sci Ltd Publicador: Elsevier Sci Ltd
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
Relevância na Pesquisa
37.08%
Rainfall, vegetation characteristics and soil hydraulic properties influence deep drainage patterns in agricultural landscapes, but more information is required on the variability of their interactions with site conditions. Therefore, the objective of the study was to investigate the impact of the interactions of soil permeability, vegetation rooting depth and growth duration on drainage in 3 sites in northern New South Wales, Australia. Local sensitivity analysis was used on drainage estimated by two biophysical models—WaterMod 3, with a crop growth module, and HYDRUS-1D without a crop growth module. The effect of saturated hydraulic conductivity (Ks), growth duration (GD), rooting depth (RD), annual rainfall, and their interactions on deep drainage was evaluated at 3 sites. Simulations were conducted using 30 years of randomly selected climate data from 115 years historical data. Rainfall variability was similar in all 3 sites, so annual rainfall was the dominant factor dictating drainage in all 30 rainfall-years whereas GD was more important than RD after accounting for rainfall and drainage was least sensitive to Ks. The minor impact of RD was ascribed to the soil water content being at the lower extraction limit of crops due to potential evaporation being greater than rainfall in almost all months of the rainfall-year. The importance of GD varied between rainfall-years and sites...

A conditional disaggregation algorithm for generating fine time-scale rainfall data in a warmer climate

Westra, S.; Evans, J.; Mehrotra, R.; Sharma, A.
Fonte: Elsevier Science BV Publicador: Elsevier Science BV
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
Relevância na Pesquisa
37.07%
This paper describes an algorithm for disaggregating daily rainfall into sub-daily rainfall ‘fragments’ (fine-resolution rainfall sequences) under a future, warmer climate. The algorithm uses a combined generalised additive model (GAM) and method of fragments (MoFs) framework to resample sub-daily rainfall fragments from the historical record conditional on daily rainfall amount and a range of atmospheric covariates. The rationale is that as the atmosphere warms, future rainfall patterns will be more reflective of historical rainfall patterns corresponding to warmer days at the same location, or to locations which have an atmospheric profile more reflective of expected future climate. It was found that the daily to sub-daily scaling relationship varied significantly by season and by location, with rainfall patterns on warmer seasons or at warmer locations typically showing more intense rainfall occurring over shorter periods compared with cooler seasons and stations. Importantly, by regressing against atmospheric covariates such as temperature, this effect was substantially reduced, suggesting that the approach may also be valid when extrapolating to a future climate. The GAM–MoF algorithm was then applied to nine stations around Australia...

Análise da variabilidade da precipitação pluvial na bacia do rio Paranapanema, em diferentes escalas; Analysis of rainfall variability in the Paranapanema river basin using different scales

Maria Alice Borges Batista
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 26/08/2015 PT
Relevância na Pesquisa
37.05%
Este trabalho foi desenvolvido com o objetivo de avaliar a dinâmica pluvial dentro dos limites da bacia do rio Paranapanema, através da variabilidade das chuvas. Foram usadas séries de precipitação pluviométricas retiradas do site Hidroweb, da Agencia Nacional de Águas (ANA), com as quais foram trabalhados os dados diários, médias mensais, desvio padrão, coeficiente de variação, máximo, mínimo, amplitude, anomalias, Índice de Anomalia de Chuva (IAC) e fator R da Equação Universal de Perda de Solo para dois recortes temporais 1976 a 2010 (34 anos) e de 1950 a 2010 (60 anos). Também foram analisados alguns anos de El Niño (1982, 1983, 1992, 1997, 2002 e 2006) e La Niña (1976, 1984, 1985, 1988, 1996 e 2008). Foram calculados Índices de Concentrações (IC ou CI da sigla em Inglês Concentration Index), para os dados diários, com intervalo de 1 mm. Também se analisou a distribuição espacial e temporal das séries de dados de chuva para a avaliação da variabilidade pluviométrica da área de estudo. Alguns resultados obtidos mostram que ao sul e sudeste da bacia, onde estão às altitudes mais elevadas, as precipitações pluviométricas foram maiores e mais regulares para os recortes temporais estudados. Os cálculos do desvio padrão mostram que houve uma variabilidade significativa...

Estimating rainfall erosivity from daily precipitation records: a comparison among methods using data from the Ebro Basin (NE Spain)

Angulo-Martínez, Marta; Beguería, Santiago
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 968098 bytes; application/pdf
ENG
Relevância na Pesquisa
37.09%
Among the major factors controlling soil erosion, as vegetation cover or soil erodibility, rainfall erosivity has a paramount importance since it is difficult to predict and control by humans. Accurate estimation of rainfall erosivity requires continuous rainfall data; however, such data rarely demonstrate good spatial and temporal coverage. Daily weather records are now commonly available, providing good coverage that better represents rainfall intensity behavior than do more aggregated rainfall data. In the present study annual rainfall erosivity was estimated from daily rainfall records, and compared to data obtained employing the RUSLE R factor procedure. A spatially-dense precipitation database of high temporal resolution (15 min) was used. Two methodologies were applied: (i) daily rainfall erosivity estimated using several parametric models, and, (ii) annual rainfall erosivity estimated by regression-based techniques employing several intensity precipitation indices and the modified Fournier index. To determine the accuracy of estimates, several goodness-of-fit and error statistics were computed in addition to a spatial distribution comparison. The daily rainfall erosivity models accurately predicted annual rainfall erosivity. Parametric models with few combined parameters and a periodic function simulating intra-annual rainfall behavior provided the best results. Where daily rainfall records were not available...

Improved rainfall estimation over the Indian monsoon region by synergistic use of Kalpana-1 and rain gauge data

Gairola,R. M.; Prakash,Satya; Pal,P. K.
Fonte: Centro de Ciencias de la Atmósfera, UNAM Publicador: Centro de Ciencias de la Atmósfera, UNAM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2015 EN
Relevância na Pesquisa
37.05%
In this paper, an attempt has been made to estimate rainfall over the Indian monsoon region by the synergistic use of the geostationary Kalpana-1 satellite-derived INSAT Multispectral Rainfall Algorithm (IMSRA) rainfall estimates and rain gauge data, using a successive correction method in order to further refine the operational IMSRA rainfall estimates. The successive correction method benefits from high spatial and temporal resolutions of the Kalpana-1 satellite and accurate rainfall estimates from rain gauges. A preliminary analysis is done for the southwest monsoon season of 2010 at a daily scale. The successive correction method is applied at a 1° latitude x 1° longitude resolution determined by the spatial autocorrelation analysis. Results are compared with four independent global multisatellite rainfall products, namely the Global Satellite Mapping of Precipitation, the Tropical Rainfall Measuring Mission Multisatellite Precipitation Analysis near-real time and research version rainfall monitoring products, and the Global Precipitation Climatology Project rainfall product. The objectively analyzed rainfall estimates show noticeable improvement over the satellite-based rainfall estimates alone over southern India. Comparison with independent rain gauge observations shows a considerable improvement in terms of correlation...

Observations on daily rainfall events in the KwaZulu-Natal Drakensberg

Nel,W
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2008 EN
Relevância na Pesquisa
37.04%
Five-minute rainfall data measured at different stations in the KwaZulu-Natal Drakensberg are presented and although the data are limited this paper is the first to analyse individual rainfall events in the area. The occurrence of rain days in the Drakensberg shows strong seasonality with most rain recorded during the summer months. Although the number of rain days as well as the number of rainfall events increases with an increase in altitude, the mean daily rainfall and mean rainfall generated from individual events is less on the escarpment than in the foothills. All stations show a high percentage of rain days with single rainfall events as well as a high proportion of rainfall received from events generating more than 10 mm, but the escarpment station receives less rainfall from these events than the stations in the foothills. It is known that rainfall in the Drakensberg is mostly generated from thunderstorms, and data presented here indicate that rainfall predominately occurs in the late afternoon/early evening when sufficient cooling has possibly taken place for condensation and cloud formation to occur.

Characterisation of rainfall at a semi-arid ecotope in the Limpopo Province (South Africa) and its implications for sustainable crop production

Mzezewa,Jestinos; Misi,Titus; van Rensburg,Leon D
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/01/2010 EN
Relevância na Pesquisa
37.04%
Detailed knowledge of rainfall regime is an important prerequisite for agricultural planning. Despite the importance of rain-fed agriculture to food security in the semi-arid regions of South Africa, studies to understand the spatial and temporal variability of rainfall are not widely documented. Twenty-three years (1983 to 2005) of rainfall data were analysed in order to study the basic statistical rainfall characteristics at the University of Venda ecotope. Annual and monthly rainfall was fitted to theoretical probability distributions. The Anderson-Darling goodness-of-fit test was used to evaluate best fit models. Probability of receiving annual and monthly rainfall was predicted using the appropriate probability distribution functions. The chance of experiencing dry spells of different durations was determined. Cumulative frequency analysis of daily rainfall amounts and depths was characterized. It was found that the distribution of daily rainfall was highly skewed with high frequency of occurrence of low-rainfall events. The distribution of daily rainfall depths was also highly skewed, a comparatively small proportion of rainy days supplying a high proportion of the rainfall.

Investigation into increasing short-duration rainfall intensities in South Africa

Du Plessis,JA; Burger,GJ
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/04/2015 EN
Relevância na Pesquisa
37.04%
Extreme storms in South Africa and specifically in the Western Cape have been responsible for widespread destruction to property and infrastructure, even leading to displacement and death. The occurrences of these storms have been increasingly linked to human-induced climate change that is expected to cause more variable weather. Studies on climate circulation models for future climate conditions project that rainfall in the Western Cape and wider South African region is to become more intense and extreme. Sub-daily rainfall for 3 stations in the Western Cape and 4 stations in the rest of South Africa were analysed in order to determine if any trends towards more intense and extreme rainfall are observed and whether the trend is unique to the Western Cape or indicates a wider trend. This study explores this expectation by using historical short-duration rainfall (less than 24 h) for 7 stations in the Western Cape and South African region. Digitised autographic and automatic weather station 5-min rainfall data were combined to extend the effective record length. Both the magnitude and frequency of occurrence of rainfall events were analysed to assess if rainfall intensities are showing any evidence of increasing over time. For the magnitude of rainfall events...

Merged rainfall fields for continuous simulation modelling (CSM)

Frezghi,MS; Smithers,JC
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2008 EN
Relevância na Pesquisa
37.09%
Long sequences of rainfall at fine spatial and temporal detail are increasingly required, not only for hydrological studies, but also to provide inputs for models of crop growth, landfills, tailings dams, liquid waste disposal on land and other environmentally sensitive projects. Rainfall information derived from rain gauges, radar or satellites may not individually be adequate to meet the detail required by hydrological models or other water resource studies. Therefore, a suitable technique is required to estimate rainfall at finer spatial and temporal resolutions. Different techniques have been developed to merge rainfall information from rain gauges, radar and satellites in order to obtain the 'best' estimate of the 'true' rainfall field. However, the length of the radar and satellite estimated rainfall records is currently limited. In this study, the mean areal merged rainfall, derived from rain gauges and radar, was estimated for 26 subcatchments in the Liebenbergsvlei catchment, which is a research catchment, in South Africa for the period when radar data were available. By using the relationships derived between the merged rainfall and rain-gauge data, improved subcatchment rainfall may be estimated using the historical data from rain gauges located in and around the subcatchments. In most of the subcatchments the relationship between the daily mean areal merged rainfall of the subcatchment and the daily rainfall data from rain gauges is strong (R² > or = 0.5). The relationship between the daily rain gauges and mean areal merged rainfall of the subcatchments is used to adjust the historical rainfall data from the daily rain gauges in order to estimate long sequences of subcatchment rainfall for input to continuous simulation models (CSMs).

Comparing available rainfall gridded datasets for West Africa and the impact on rainfall-runoff modelling results, the case of Burkina-Faso

Mahe,Gil; Girard,Sabine; New,Mark; Paturel,Jean-Emmanuel; Cres,Agnes; Dezetter,Alain; Dieulin,Claudine; Boyer,Jean-François; Rouche,Nathalie; Servat,Eric
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2008 EN
Relevância na Pesquisa
37.07%
Monthly rainfall data in Burkina-Faso, West Africa, over a period of 77 years are extracted from three different gridded data sets, available either on the web: CRU (Climatic Research Unit, Norwich, UK), SIEREM (HydroSciences Montpellier, France), or from the National Meteorological Center of Burkina-Faso. With a view to modelling the runoff-rainfall relationship at the monthly time step, these data are used at the 0.5°*0.5° scale. Despite mean, minimum, standard deviation and inter-annual variability being very similar for the period 1922 to 1998, the three gridded data sets used show an important spatial variability of values with time, and some differences are observed which lead to significantly different runoff-rainfall simulations. Comparison of the rainfall grids has shown that differences between the precipitation grids are more pronounced during years when the rainfall is lower; this also applies to areas where the rainfall is lower. The three different rainfall grids produce differences in mean rainfall of 4 to 11%, depending on the grids that are compared. While these results are obviously specific to the station networks and interpolation method used, they provide an indication of the differences that can arise. It is recommended that as many stations as possible are used to better assess areal rainfall. These biases have a strong influence on the results of the runoff-rainfall modelling (using the GR2M conceptual model): the Nash criteria show differences of about 20% and calculated flow of 30% to 40%. This study illustrates the levels of uncertainty when using available rainfall gridded data sets...

Heavy daily-rainfall characteristics over the Gauteng Province

Dyson,Liesl L
Fonte: Water SA Publicador: Water SA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2009 EN
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Daily rainfall over the Gauteng Province, South Africa, was analysed for the summer months of October to March using 32-yr (1977 to 2009) daily rainfall data from about 70 South African Weather Service stations. The monthly and seasonal variation of heavy rainfall occurrences was also analysed. Three 24-h heavy rainfall classes are defined considering the area-average rainfall. A significant rainfall event is defined when the average rainfall exceeds 10 mm, a heavy rainfall event when the average rainfall exceeds 15 mm and a very heavy rainfall event when the average rainfall exceeds 25 mm. January months have the highest monthly average rainfall as well as the highest number of heavy and very heavy rainfall days. The month with the second-highest number of heavy and very heavy rainfall days is February followed by March and October. December has the second-highest monthly average rainfall and the most days with rain. However, it is also the month with the lowest number of heavy and very heavy rainfall days. The highest 24-h rainfall recorded at a single station during the 32-yr period was 300 mm in December 2006. However, rainfall exceeding 115 mm at a single rainfall station in the Gauteng Province is very rare and does not occur every year. January months receive these events more than any other month but this only transpires in approximately a third of years. The central and north-western parts of the Province experience the most events where the rainfall at a single station surpasses 75 and 115 mm. With regard to seasonal rainfall...