SANTOS, Julio Cesar Neves dos. Processos hidrológicos e sedimentológicos em clima semiárido tropical. 2015. 167 f. Tese (doutorado em engenharia agrícola)- Universidade Federal do Ceará, Fortaleza-CE, 2015. / Submitted by Elineudson Ribeiro (elineudsonr@gmail.com) on 2016-03-22T20:20:32Z No. of bitstreams: 1 2016_tese_jcnsantos.pdf: 7356479 bytes, checksum: d9f566594ccbc8e17ca265d0b238223a (MD5) / Approved for entry into archive by José Jairo Viana de Sousa (jairo@ufc.br) on 2016-05-18T19:37:55Z (GMT) No. of bitstreams: 1 2016_tese_jcnsantos.pdf: 7356479 bytes, checksum: d9f566594ccbc8e17ca265d0b238223a (MD5) / Made available in DSpace on 2016-05-18T19:37:55Z (GMT). No. of bitstreams: 1 2016_tese_jcnsantos.pdf: 7356479 bytes, checksum: d9f566594ccbc8e17ca265d0b238223a (MD5) Previous issue date: 2015 / The understanding of processes such as the generation of surface runoff, sediment yield and their relations with the rainfall regime is the basis for the planning and effective management of soil and water resources in a watershed. In this context, the present study aims to identify the main processes that influence the generation of surface runoff and sediment yield in small watersheds, and determine parameters for empirical sedimentological models, as well as the Sediment Delivery Ratio (SDR) for the tropical, semi-arid region of Brazil. The study area is the Iguatu Experimental Basin (IEB), which comprises a watershed of 16.74 km2, three small nested watersheds (from 1 to 3 ha) and three erosion plots of 20 m2. One of the watersheds had been under regenerating Caatinga for 35 years, another subjected to a management, which involved thinning the Caatinga, and the last faced deforestation followed by burning and the cultivation of grass. The period of study was six years (2009 to 2014). Collections to quantify surface runoff and sediment yield were taken for each erosive rainfall event in an accumulated period of 24 hours. Surface runoff in the watersheds was quantified using Parshall flumes, and sediment yield was measured with towers and trenches to collect suspended sediment and bedload. On the watershed scale, runoff was measured by means of a spillway, and sediment yield by a turbidimeter. Cluster analysis was used to determine rainfall regimes and groups of similar rainfall-runoff events. With data from the erosion plots and watersheds, the C factors and coefficients of the Modified Universal Soil Loss Equation (MUSLE) were calibrated and validated. From data measured in the basin, sediment delivery ratios were determined. The occurrence of dry spells and the formation of cracks in the soil were important factors in controlling the generation of runoff and consequently sediment yield. The dry spells made it possible for the soil to dry out, with the formation of cracks, which acted as pathways for preferential flow, generating higher initial abstraction during the start of the rainy season. Changes in ground cover had little influence on accumulated flow, demonstrating that the soil characteristics and conditions as moisture and the presence of cracks, best explain the generation of runoff on expansive soils. The greatest runoff losses in all the watersheds under study were for Rainfall Regime II, characterized by higher depth, intensity and occurrence of the rainfall. For the ground covers under study, values for the C factors and the fit of the coefficients "a" and "b" of MUSLE, proved to be appropriate and recommended according to the statistical indices employed. Values for sediment delivery ratio for individual rainfall events ranged from 0.08 to 1.67%, with an average of 0.68%. In the basin, extreme events may cause high disaggregation of soil particles, but without sufficient transporting energy for dragging the sediment, generating low SDR. / O entendimento de processos como geração do escoamento superficial, produção de sedimentos e suas relações com o regime pluviométrico é a base para o planejamento e a gestão eficaz dos recursos solo e água em uma bacia hidrográfica. Nesse contexto, o presente estudo tem como objetivos identificar os principais processos que influenciam a geração do escoamento superficial e a produção de sedimento em pequenas bacias hidrográficas, e calibrar parâmetros de modelos sedimentológicos empíricos, bem como a razão de aporte de sedimentos (SDR) para a região semiárida tropical do Brasil. A área de estudo é a Bacia Experimental de Iguatu (BEI), composta de uma bacia de 16,74 km2, três pequenas microbacias aninhadas (de 1 a 3 ha) e três parcelas de erosão de 20 m2. Uma das microbacias foi mantida com Caatinga em regeneração há 35 anos, outra submetida ao manejo de raleamento da Caatinga e na última foi realizado o desmatamento seguido de queimada e cultivo de capim. O período de estudo foi de seis anos (2009 a 2014). As coletas para quantificação do escoamento superficial e da produção de sedimentos foram realizadas a cada evento de chuva erosiva, no acumulado de 24 horas. O escoamento superficial nas microbacias foi quantificado através de calhas Parshall e as produções de sedimentos foram mensuradas através de torres e fossos coletores de sedimentos em suspensão e arraste. Na bacia de 16,74 km2, o escoamento superficial foi mensurado por meio de um vertedor e a produção de sedimentos através de um turbidímetro. Análises de agrupamento foram utilizadas para determinação de regimes de chuvas e grupos de eventos similares de chuva-deflúvio. Com dados das parcelas de erosão e das microbacias foram calibrados e validados os fatores C e os coeficientes da Equação Universal de Perdas de Solo Modificada (MUSLE). A partir dos dados medidos na bacia foram determinadas as razões de aporte de sedimentos. A ocorrência de veranicos e a formação de fendas no solo foram determinantes no controle da geração de escoamento e consequentemente da produção de sedimentos. A ocorrência de veranicos possibilitou o secamento do solo com a formação de fendas, que agem como caminhos preferenciais para o fluxo de água, gerando elevadas abstrações inicias durante o início da estação chuvosa. As mudanças da cobertura vegetal apresentaram pouca influência sobre o escoamento acumulado, indicando que as características e condições do solo, como umidade e presença de fendas, explicam melhor a geração de escoamento em solos expansivos. Maiores perdas por escoamento em todas as microbacias estudadas foram para chuvas do Regime II caracterizado por maiores alturas pluviométricas, intensidades e ocorrências. Quanto aos valores dos fatores C e dos coeficientes de ajuste “a” e “b” da MUSLE, para as coberturas estudadas, mostraram-se apropriados e recomendados de acordo com os índices estatísticos empregados. Os valores da razão de aporte de sedimentos para eventos pluviométricos individuais variaram de 0,08 a 1,67%, com média de 0,68%. Na bacia, eventos extremos podem causar elevada desagregação de partículas de solo, mas podem não dispor de energia de transporte suficiente para arrastá-las, gerando baixo SDR.

A atividade agrícola é muito importante para a economia do Rio Grande do Sul, cuja região alvo deste estudo é sua porção noroeste, representada por seis municípios: São Luiz Gonzaga, Santa Rosa, Cruz Alta, Iraí, Passo Fundo e Marcelino Ramos. Esta região é foco nacional de produção de soja, dependendo fortemente das condições atmosféricas, tanto em escala sinótica quanto climática. Os períodos secos, conhecidos como veranicos, durante a fase de desenvolvimento até a colheita, que acorrem entre outubro e março, acarretam vários prejuízos à região. O objetivo do trabalho é estimar a climatologia de ocorrência de veranicos no NW do RS, no primeiro e quarto trimestres do ano, entre 1978 e 2005 e associá-los a padrões atmosféricos característicos. Verificou-se que o maior número de veranicos ocorre no primeiro trimestre em relação ao quarto, resultado que apresenta correlação direta com o volume médio climatológico de precipitação para esses 2 trimestres. Março e dezembro apresentam mais eventos secos do que os outros meses, o que parece ser resposta direta de menor volume de chuva. Por outro lado, numa análise espacial, Santa Rosa e São Luiz Gonzaga apresentam os maiores números de veranicos, mesmo com médias anuais climatológicas de precipitação superior aos demais municípios. Durante os períodos secos (úmidos) verificou-se o padrão dipolo com base na ROL. Nesses períodos, no sul do Brasil foram observados baixos (altos) valores de ROL, em relação à média climatológica. Sobre o norte e nordeste do Brasil há a inversão das anomalias de ROL, configurando o dipolo. Anomalias de convergência (divergência) em altos níveis são observadas sobre boa parte do sul do Brasil e oceano Atlântico adjacente, durante períodos secos (úmidos), fornecendo desta forma, maior divergência em baixos níveis. A circulação do ar em períodos úmidos (secos) evidencia a intensificação (enfraquecimento) do JBN em direção ao sul do Brasil, contribuindo para o incremento (decréscimo) de chuvas na região. Anomalias negativas e positivas de TSM sobre o Pacífico Equatorial parecem influir em todos os meses selecionados a variabilidade de precipitação no sul e a variabilidade da TSM do Atlântico Subtropical, adjacente à Região Sul do País, não influencia diretamente a variabilidade de chuvas sobre o RS. Assim, conclui-se que períodos de veranicos ou úmidos são descritos por padrões climáticos definidos. / Agriculture plays an extremely important role in the economy of Rio Grande do Sul state. The target region of the present work in its northwest portion is represented by six cities: São Luiz Gonzaga, Santa Rosa, Cruz Alta, Iraí, Passo Fundo e Marcelino Ramos. It constitute a national focus of soya production and thus depend heavily on atmospheric conditions not only in the synoptic scale but also in climatic. In dry spells periods (known as veranicos in portuguese), during growing to harvest and, comprehending the months from October to March, the frequent lack of rain brings great economic losses to the region. The aim of this work is to estimate the climatology of dry spells occurrence in the northwest portion of Rio Grande do Sul in the first and fourth quarters of the year, between 1978 and 2005. Related to extreme climatic periods and the greater occurrence of dry spells, we depicted atmospheric and oceanic patterns. In conclusion, it is stated that the number of dry spells that occur in the first quarter of the year is greater than that which take place in the fourth quarter what is directly related to the monthly precipitation climatology. Santa Rosa is the municipality which presents the greater number of dry spells, even with higher monthly climatologic average than the other locations. March and December present more events than the other months, what in this case is related to the low amount of precipitation. During dry and wet periods, there is the evidence of a dipole standard based on ROL data. During dry (wet) periods in the southern part of Brazil it is observed low (high) values of ROL, in relation to climatology. Over the northern region of Brazil, during the same periods, it is observed inverted ROL anomalies, figuring the dipole pattern. An anomalous convergence (divergence) region in high levels above part of the South Region and the adjacent South Atlantic is observed during dry (wet) periods. The circulation pattern in low atmospheric levels, during wet (dry) periods, shows the strengthening (weakening) of the meridional low levels jet, which contributes for the increase (decrease) of rain in the region. ENSO events are somehow connected to the occurrence of dry spells in the region of study. All the considered month during dry (wet) periods in climatic extremes are related to negative (positive) TSM anomalies in the Equatorial Pacific region, that is, to La Niña (El Niño) events. This strong relation between precipitation variability and surface temperature anomalies over South Atlantic is not so evident. In conclusion, the occurrence of dry spells periods is well related to extreme climatic conditions.

A atividade agrícola é muito importante para a economia do Rio Grande do Sul, cuja região alvo deste estudo é sua porção noroeste, representada por seis municípios: São Luiz Gonzaga, Santa Rosa, Cruz Alta, Iraí, Passo Fundo e Marcelino Ramos. Esta região é foco nacional de produção de soja, dependendo fortemente das condições atmosféricas, tanto em escala sinótica quanto climática. Os períodos secos, conhecidos como veranicos, durante a fase de desenvolvimento até a colheita, que acorrem entre outubro e março, acarretam vários prejuízos à região. O objetivo do trabalho é estimar a climatologia de ocorrência de veranicos no NW do RS, no primeiro e quarto trimestres do ano, entre 1978 e 2005 e associá-los a padrões atmosféricos característicos. Verificou-se que o maior número de veranicos ocorre no primeiro trimestre em relação ao quarto, resultado que apresenta correlação direta com o volume médio climatológico de precipitação para esses 2 trimestres. Março e dezembro apresentam mais eventos secos do que os outros meses, o que parece ser resposta direta de menor volume de chuva. Por outro lado, numa análise espacial, Santa Rosa e São Luiz Gonzaga apresentam os maiores números de veranicos, mesmo com médias anuais climatológicas de precipitação superior aos demais municípios. Durante os períodos secos (úmidos) verificou-se o padrão dipolo com base na ROL. Nesses períodos, no sul do Brasil foram observados baixos (altos) valores de ROL, em relação à média climatológica. Sobre o norte e nordeste do Brasil há a inversão das anomalias de ROL, configurando o dipolo. Anomalias de convergência (divergência) em altos níveis são observadas sobre boa parte do sul do Brasil e oceano Atlântico adjacente, durante períodos secos (úmidos), fornecendo desta forma, maior divergência em baixos níveis. A circulação do ar em períodos úmidos (secos) evidencia a intensificação (enfraquecimento) do JBN em direção ao sul do Brasil, contribuindo para o incremento (decréscimo) de chuvas na região. Anomalias negativas e positivas de TSM sobre o Pacífico Equatorial parecem influir em todos os meses selecionados a variabilidade de precipitação no sul e a variabilidade da TSM do Atlântico Subtropical, adjacente à Região Sul do País, não influencia diretamente a variabilidade de chuvas sobre o RS. Assim, conclui-se que períodos de veranicos ou úmidos são descritos por padrões climáticos definidos. / Agriculture plays an extremely important role in the economy of Rio Grande do Sul state. The target region of the present work in its northwest portion is represented by six cities: São Luiz Gonzaga, Santa Rosa, Cruz Alta, Iraí, Passo Fundo e Marcelino Ramos. It constitute a national focus of soya production and thus depend heavily on atmospheric conditions not only in the synoptic scale but also in climatic. In dry spells periods (known as veranicos in portuguese), during growing to harvest and, comprehending the months from October to March, the frequent lack of rain brings great economic losses to the region. The aim of this work is to estimate the climatology of dry spells occurrence in the northwest portion of Rio Grande do Sul in the first and fourth quarters of the year, between 1978 and 2005. Related to extreme climatic periods and the greater occurrence of dry spells, we depicted atmospheric and oceanic patterns. In conclusion, it is stated that the number of dry spells that occur in the first quarter of the year is greater than that which take place in the fourth quarter what is directly related to the monthly precipitation climatology. Santa Rosa is the municipality which presents the greater number of dry spells, even with higher monthly climatologic average than the other locations. March and December present more events than the other months, what in this case is related to the low amount of precipitation. During dry and wet periods, there is the evidence of a dipole standard based on ROL data. During dry (wet) periods in the southern part of Brazil it is observed low (high) values of ROL, in relation to climatology. Over the northern region of Brazil, during the same periods, it is observed inverted ROL anomalies, figuring the dipole pattern. An anomalous convergence (divergence) region in high levels above part of the South Region and the adjacent South Atlantic is observed during dry (wet) periods. The circulation pattern in low atmospheric levels, during wet (dry) periods, shows the strengthening (weakening) of the meridional low levels jet, which contributes for the increase (decrease) of rain in the region. ENSO events are somehow connected to the occurrence of dry spells in the region of study. All the considered month during dry (wet) periods in climatic extremes are related to negative (positive) TSM anomalies in the Equatorial Pacific region, that is, to La Niña (El Niño) events. This strong relation between precipitation variability and surface temperature anomalies over South Atlantic is not so evident. In conclusion, the occurrence of dry spells periods is well related to extreme climatic conditions.

A cana-de-açúcar é um dos principais produtos agrícolas cultivados no Brasil. O País é o maior produtor de cana-de-açúcar do mundo, sendo que o Estado de São Paulo é responsável por 57,5 % da produção brasileira. Como em qualquer outra cultura, as condições atmosféricas constituem um dos principais fatores responsáveis pela quebra na produtividade. A fim de determinar as regiões paulistas mais susceptíveis a eventos de tempo prejudiciais ao cultivo canavieiro, principalmente com relação ao déficit hídrico, foram calculadas as probabilidades de ocorrência de períodos secos no Estado para o período de 1971-2003. Os resultados mostraram que as regiões centro-norte e centro-oeste paulistas são as que possuem condições pluviométricas mais adequadas às exigências hídricas da cana-de-açúcar, com estações seca e chuvosa mais bem definidas do que nas demais regiões. Foram encontradas seis regiões homogêneas dentro do Estado quanto ao regime de precipitação, sendo que quatro destas são áreas canavieiras. Para estas quatro regiões, foram determinadas as datas de início e fim da estação chuvosa, de modo a selecionar veranicos que ocorreram dentro da mesma e que possam ter prejudicado a produção de cana no Estado. Para esses períodos, foram construídos campos médios para diferentes variáveis meteorológicas, defasados no tempo em até 3 pêntadas. A comparação entre os campos médios obtidos e campos observados em sete episódios de veranicos mostra que o campo de divergência de massa é o mais indicado na previsão dos mesmos, com 70 a 100 % de semelhanças nas características meteorológicas identificadas. Por fim, análises foram feitas sobre a existência de mudanças no padrão de precipitação das regiões canavieiras paulistas. Foi possível concluir que a quantidade de chuva acumulada nos meses de DJF apresentou tendência de aumento no período 1937-2003, assim como o número de dias de chuva maior que 1 mm, indicando um aumento do número de eventos extremos de precipitação. A análise da tendência da estação chuvosa nas quatro regiões homogêneas de interesse mostrou antecipação (atraso) no início (fim) da época das chuvas no interior do Estado, ocasionando um prolongamento na duração da estação chuvosa. / Sugarcane is one of the major agricultural products grown in Brazil. The country is the largest sugarcane producer in the world, and São Paulo State accounts for 57,5 % of Brazilian production. As in any other culture, the weather conditions play an important role on production losses. In order to identify the most vulnerable State regions for sugarcane cultivation, especially with respect to hydric deficit, the probabilities of dry spells in the State were calculated for the 1971-2003 period. The results showed that the rainfall conditions on the northern central and midwestern regions of São Paulo are the ones that better fulfill sugarcane water requirements, with wet and dry seasons better defined in comparison with the other regions. Based on precipitation, six homogeneous regions were determined inside the State. Four of these regions are sugar-cane production areas. The onset and end of the rainy season in these four regions were investigated in order to select dry spells that might have hindered the production of sugarcane in the State. Lagged mean atmospheric fields based on these dry spells were constructed. Comparisons between mean and observed fields during seven different dry spells showed that the divergence field is the one that can be best used in the forecast of dry spells, with resemblance of 70 to 100 % on meteorological characteristics and its mean values. Finally, tests were made in order to investigate the existence of changes in precipitation patterns over the productive regions of São Paulo. Results led to the conclusion that the amount of precipitation accumulated during de DJF trimester tended to increase during the 1937-2003 period, as well as the number of days with rainfall greater than 1 mm, indicating that the extreme precipitation events has possibly also increased. The trend analysis of the rainy season in the four homogeneous regions of interest showed early (late) start (end) of the rainy season in the countryside, causing a more extended rainy season.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / The understanding of processes such as the generation of surface runoff, sediment yield and their relations with the rainfall regime is the basis for the planning and effective management of soil and water resources in a watershed. In this context, the present study aims to identify the main processes that influence the generation of surface runoff and sediment yield in small watersheds, and determine parameters for empirical sedimentological models, as well as the Sediment Delivery Ratio (SDR) for the tropical, semi-arid region of Brazil. The study area is the Iguatu Experimental Basin (IEB), which comprises a watershed of 16.74 km2, three small nested watersheds (from 1 to 3 ha) and three erosion plots of 20 m2. One of the watersheds had been under regenerating Caatinga for 35 years, another subjected to a management, which involved thinning the Caatinga, and the last faced deforestation followed by burning and the cultivation of grass. The period of study was six years (2009 to 2014). Collections to quantify surface runoff and sediment yield were taken for each erosive rainfall event in an accumulated period of 24 hours. Surface runoff in the watersheds was quantified using Parshall flumes, and sediment yield was measured with towers and trenches to collect suspended sediment and bedload. On the watershed scale, runoff was measured by means of a spillway, and sediment yield by a turbidimeter. Cluster analysis was used to determine rainfall regimes and groups of similar rainfall-runoff events. With data from the erosion plots and watersheds, the C factors and coefficients of the Modified Universal Soil Loss Equation (MUSLE) were calibrated and validated. From data measured in the basin, sediment delivery ratios were determined. The occurrence of dry spells and the formation of cracks in the soil were important factors in controlling the generation of runoff and consequently sediment yield. The dry spells made it possible for the soil to dry out, with the formation of cracks, which acted as pathways for preferential flow, generating higher initial abstraction during the start of the rainy season. Changes in ground cover had little influence on accumulated flow, demonstrating that the soil characteristics and conditions as moisture and the presence of cracks, best explain the generation of runoff on expansive soils. The greatest runoff losses in all the watersheds under study were for Rainfall Regime II, characterized by higher depth, intensity and occurrence of the rainfall. For the ground covers under study, values for the C factors and the fit of the coefficients "a" and "b" of MUSLE, proved to be appropriate and recommended according to the statistical indices employed. Values for sediment delivery ratio for individual rainfall events ranged from 0.08 to 1.67%, with an average of 0.68%. In the basin, extreme events may cause high disaggregation of soil particles, but without sufficient transporting energy for dragging the sediment, generating low SDR. / O entendimento de processos como geraÃÃo do escoamento superficial, produÃÃo de sedimentos e suas relaÃÃes com o regime pluviomÃtrico à a base para o planejamento e a gestÃo eficaz dos recursos solo e Ãgua em uma bacia hidrogrÃfica. Nesse contexto, o presente estudo tem como objetivos identificar os principais processos que influenciam a geraÃÃo do escoamento superficial e a produÃÃo de sedimento em pequenas bacias hidrogrÃficas, e calibrar parÃmetros de modelos sedimentolÃgicos empÃricos, bem como a razÃo de aporte de sedimentos (SDR) para a regiÃo semiÃrida tropical do Brasil. A Ãrea de estudo à a Bacia Experimental de Iguatu (BEI), composta de uma bacia de 16,74 km2, trÃs pequenas microbacias aninhadas (de 1 a 3 ha) e trÃs parcelas de erosÃo de 20 m2. Uma das microbacias foi mantida com Caatinga em regeneraÃÃo hà 35 anos, outra submetida ao manejo de raleamento da Caatinga e na Ãltima foi realizado o desmatamento seguido de queimada e cultivo de capim. O perÃodo de estudo foi de seis anos (2009 a 2014). As coletas para quantificaÃÃo do escoamento superficial e da produÃÃo de sedimentos foram realizadas a cada evento de chuva erosiva, no acumulado de 24 horas. O escoamento superficial nas microbacias foi quantificado atravÃs de calhas Parshall e as produÃÃes de sedimentos foram mensuradas atravÃs de torres e fossos coletores de sedimentos em suspensÃo e arraste. Na bacia de 16,74 km2, o escoamento superficial foi mensurado por meio de um vertedor e a produÃÃo de sedimentos atravÃs de um turbidÃmetro. AnÃlises de agrupamento foram utilizadas para determinaÃÃo de regimes de chuvas e grupos de eventos similares de chuva-deflÃvio. Com dados das parcelas de erosÃo e das microbacias foram calibrados e validados os fatores C e os coeficientes da EquaÃÃo Universal de Perdas de Solo Modificada (MUSLE). A partir dos dados medidos na bacia foram determinadas as razÃes de aporte de sedimentos. A ocorrÃncia de veranicos e a formaÃÃo de fendas no solo foram determinantes no controle da geraÃÃo de escoamento e consequentemente da produÃÃo de sedimentos. A ocorrÃncia de veranicos possibilitou o secamento do solo com a formaÃÃo de fendas, que agem como caminhos preferenciais para o fluxo de Ãgua, gerando elevadas abstraÃÃes inicias durante o inÃcio da estaÃÃo chuvosa. As mudanÃas da cobertura vegetal apresentaram pouca influÃncia sobre o escoamento acumulado, indicando que as caracterÃsticas e condiÃÃes do solo, como umidade e presenÃa de fendas, explicam melhor a geraÃÃo de escoamento em solos expansivos. Maiores perdas por escoamento em todas as microbacias estudadas foram para chuvas do Regime II caracterizado por maiores alturas pluviomÃtricas, intensidades e ocorrÃncias. Quanto aos valores dos fatores C e dos coeficientes de ajuste âaâ e âbâ da MUSLE, para as coberturas estudadas, mostraram-se apropriados e recomendados de acordo com os Ãndices estatÃsticos empregados. Os valores da razÃo de aporte de sedimentos para eventos pluviomÃtricos individuais variaram de 0,08 a 1,67%, com mÃdia de 0,68%. Na bacia, eventos extremos podem causar elevada desagregaÃÃo de partÃculas de solo, mas podem nÃo dispor de energia de transporte suficiente para arrastÃ-las, gerando baixo SDR.

A cana-de-açúcar é um dos principais produtos agrícolas cultivados no Brasil. O País é o maior produtor de cana-de-açúcar do mundo, sendo que o Estado de São Paulo é responsável por 57,5 % da produção brasileira. Como em qualquer outra cultura, as condições atmosféricas constituem um dos principais fatores responsáveis pela quebra na produtividade. A fim de determinar as regiões paulistas mais susceptíveis a eventos de tempo prejudiciais ao cultivo canavieiro, principalmente com relação ao déficit hídrico, foram calculadas as probabilidades de ocorrência de períodos secos no Estado para o período de 1971-2003. Os resultados mostraram que as regiões centro-norte e centro-oeste paulistas são as que possuem condições pluviométricas mais adequadas às exigências hídricas da cana-de-açúcar, com estações seca e chuvosa mais bem definidas do que nas demais regiões. Foram encontradas seis regiões homogêneas dentro do Estado quanto ao regime de precipitação, sendo que quatro destas são áreas canavieiras. Para estas quatro regiões, foram determinadas as datas de início e fim da estação chuvosa, de modo a selecionar veranicos que ocorreram dentro da mesma e que possam ter prejudicado a produção de cana no Estado. Para esses períodos, foram construídos campos médios para diferentes variáveis meteorológicas, defasados no tempo em até 3 pêntadas. A comparação entre os campos médios obtidos e campos observados em sete episódios de veranicos mostra que o campo de divergência de massa é o mais indicado na previsão dos mesmos, com 70 a 100 % de semelhanças nas características meteorológicas identificadas. Por fim, análises foram feitas sobre a existência de mudanças no padrão de precipitação das regiões canavieiras paulistas. Foi possível concluir que a quantidade de chuva acumulada nos meses de DJF apresentou tendência de aumento no período 1937-2003, assim como o número de dias de chuva maior que 1 mm, indicando um aumento do número de eventos extremos de precipitação. A análise da tendência da estação chuvosa nas quatro regiões homogêneas de interesse mostrou antecipação (atraso) no início (fim) da época das chuvas no interior do Estado, ocasionando um prolongamento na duração da estação chuvosa. / Sugarcane is one of the major agricultural products grown in Brazil. The country is the largest sugarcane producer in the world, and São Paulo State accounts for 57,5 % of Brazilian production. As in any other culture, the weather conditions play an important role on production losses. In order to identify the most vulnerable State regions for sugarcane cultivation, especially with respect to hydric deficit, the probabilities of dry spells in the State were calculated for the 1971-2003 period. The results showed that the rainfall conditions on the northern central and midwestern regions of São Paulo are the ones that better fulfill sugarcane water requirements, with wet and dry seasons better defined in comparison with the other regions. Based on precipitation, six homogeneous regions were determined inside the State. Four of these regions are sugar-cane production areas. The onset and end of the rainy season in these four regions were investigated in order to select dry spells that might have hindered the production of sugarcane in the State. Lagged mean atmospheric fields based on these dry spells were constructed. Comparisons between mean and observed fields during seven different dry spells showed that the divergence field is the one that can be best used in the forecast of dry spells, with resemblance of 70 to 100 % on meteorological characteristics and its mean values. Finally, tests were made in order to investigate the existence of changes in precipitation patterns over the productive regions of São Paulo. Results led to the conclusion that the amount of precipitation accumulated during de DJF trimester tended to increase during the 1937-2003 period, as well as the number of days with rainfall greater than 1 mm, indicating that the extreme precipitation events has possibly also increased. The trend analysis of the rainy season in the four homogeneous regions of interest showed early (late) start (end) of the rainy season in the countryside, causing a more extended rainy season.

De par sa géométrie et sa situation géographique (2°N-13°N – 8°E-16°E ; ouverture sur l’océan Atlantique), le Cameroun offre l’avantage de proposer un ensemble représentatif des climats régionaux rencontrés en Afrique tropicale. La diminution des cumuls de précipitations enregistrée dans la région pendant la seconde moitié du XXe siècle, est associée à la récurrence de périodes anormalement sèches, essentiellement au cœur de la saison des pluies. Ces conditions ont amplifié la dégradation du couvert végétal au travers ses contraintes socioéconomiques et démographiques (déforestation, extension des surfaces d’activité). Les conséquences souvent dommageables de la variabilité climatique en général, et des sécheresses en particulier, sur les hommes et leurs activités suscitent l’intérêt de développer des études pour mieux comprendre comment le climat et les pressions naturelles et environnementales interagissent localement. Ainsi, l’objectif de cette thèse est de diagnostiquer la variabilité multiéchelle (saisonnière, interannuelle, intra-saisonnière, synoptique) des précipitations et les relations qu’elle entretient avec le couvert végétal au sens large qui, à ces latitudes, est associé directement ou non, à la dynamique d’occupation et d’utilisation du sol, particulièrement sur la période 1951-2002. A partir de données de précipitations observées (CRU/ponctuelles), les modes spatiaux de la variabilité ont été définis aux échelles annuelles et interannuelles, par Analyses en Composante Principale (ACP) et la Classification Ascendante Hiérarchique (CAH). Ces méthodes de classifications ont permis de discriminer cinq zones climatiques, différentes les unes des autres par l’intensité des cumuls et la saisonnalité (unimodal/bimodal). Pour chaque zone, l’attention a été portée sur les paramètres intrasaisonniers qui modulent la variabilité annuelle telle que, les séquences sèches (nombre, longueur, périodes d’occurrence) et les variations des dates de début et de fin des périodes végétatives. La répartition du couvert végétal dans l’espace et dans le temps (1982-2002) a été étudiée, en utilisant des méthodes de classification non supervisée (ISODATA) sur les données de NDVI (Normalized Difference Vegetation index) à 8km de résolution. Enfin, des méthodes statistiques et de télédétection ont permis d’évaluer l’impact des facteurs pluviométriques et anthropogéniques (croissance démographique et utilisation du sol) sur la dynamique du couvert végétal en utilisant des bases de données à plus fine résolution (NDVI/1Km ; Global Land Cover (GLC 2000/1Km)). Ces dernières investigations ont été menées dans le Nord-Cameroun (6°N-13°N – 11°E-16°E), qui est la région la plus sensible des points de vue climatique, économique et environnemental. / Due to its shape and location (2°N-13°N – 8°E-16°E; proximity of the Atlantic Ocean), Cameroon is characterized by a panel of cross-regional climate encountered widely in tropical Africa. Over the region, the decrease rainfall during the second half of the last century has been shown to be associated with stronger recurrence of drier periods, specifically in the core of the rainy season. These conditions have favored the degradation of vegetation cover, driven by socioeconomic and demographic constraints. The substantial impacts on human activities and local society highlight the need to better understand how climate and environmental dynamics do interact locally. The aim of this study is to diagnose multi-scale rainfall variability and its relationship with vegetation cover (natural and/or grown), which is directly or indirectly associated to the land-cover and land-use dynamics at these latitudes. Using observed rainfall data (Climatic Research Unit/punctual), the spatial modes of rainfall variability at annual and intraseasonal scales are defined through Principal Component Analysis (PCA) and Agglomerative Hierarchical Clustering (AHC). These regionalizations lead to the discretisation of 5 climatic zones, distinguished from each other, by both the amount of rainfall and seasonality (unimodal / bimodal). New intraseasonal dry spells statistics (number, length, period of occurrence) are produced as well as dates of onset and end of the vegetative seasons by sub-regions. Using unsupervised classification methods (such as ISODATA) in Normalized Difference Vegetation Index (NDVI) data at a 8km spatial resolution, vegetation cover spatiotemporal distribution and typology were produced. Then, based on a concomitant use of statistical and GIS approaches, higher resolutions of NDVI (SPOT-1Km) and Global Land-cover data (GLC 2000), allowed to further evaluate both the pluviometric and anthropogenic factors (demography, land use) influencing vegetation dynamics. Analysis were carried out in Northern Cameroon (6°N-13°N – 11°E-16°E), which is the most sensitive region with regards to climatic and environmental variability, that could lead to important socio-economic thread locally.

Most of Eastern Africa has arid and semi-arid climate with high space-time variability in rainfall. The droughts are very common in this region, and often persist for several years, preceded or followed by extreme floods. Most of the livelihoods and socio-economic activities however remain rain-dependent leading to severe negative impacts during the periods of occurrence of climate extremes. It has been noted that one extreme event was capable of reversing national economic growth made over a period of several years. Thus no sustainable development can be attained in eastern Africa without effective mainstreaming of climate information in the development policies, plans and programmes. Many past studies in the region have focused on rainfall variability at seasonal, annual and decadal scales. Very little work has been done at intraseasonal timescale that is paramount to most agricultural applications. This study aims at filling this research gap, by investigating the structure of rainfall season in terms of the distribution of wet and dry spells and how this distribution varies in space and time at interannual time scale over Equatorial Eastern Africa. Prediction models for use in the early warning systems aimed at climate risk reduction were finally developed. The specific objectives of the study include, delineate and diagnose the some aspects of the distribution of the wet and dry spells at interannual timescale; investigate the linkages between the aspects of the distribution of wet and dry spells identified and dominant large scale climate fields that drive the global climate; and assess the predictability of the various aspects of wet and dry spells for the improvement of the use in the early warning systems of the region.Several datasets spanning a period of 40 years (1961 - 2000) were used. The data included gauged daily rainfall amount for the three Eastern Africa countries namely Kenya, Uganda, and Tanzania; Hadley Centre Sea Surface Temperature (SST); re-analysis data and radiosonde observations from Nairobi (Kenya) and Bangui (Central Africa Republic) upper air stations. The indices of El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole and SST gradients which constituted the predefined predictors were also used [...]

La plus grande partie de l’Afrique orientale présente un climat aride à semi-aride, et une forte variabilité spatio-temporelle des pluies. Les sécheresses sont courantes dans cette région, et persistent souvent sur plusieurs années consécutives, précédées ou suivies par des inondations majeures. La plupart des modes de vie et des activités socio-économiques restent néanmoins dépendants des précipitations, avec des effets extrêmement dommageables en périodes d’extrêmes climatiques. Il a été montré qu’un seul événement extrême suffisait à inverser la croissance économique nationale plusieurs années d’affilée. Aucun développement durable ne peut donc être réalisé en Afrique de l’Est sans une prise en compte effective de l’information climatique dans les politiques, les plans et les programmes de développement. De nombreuses études antérieures sur la région ont été consacrées à la variabilité des pluies aux échelles saisonnière, annuelle et décadaire. Peu de recherches ont porté sur l’échelle intra-saisonnière, qui est déterminante pour la plupart des applications agricoles. Cette étude vise à combler cette lacune, en examinant la structure de la saison des pluies en termes de répartition des épisodes secs et pluvieux, et la façon dont cette répartition varie dans l’espace et le temps, à l’échelle interannuelle à travers l’Afrique est-équatoriale. Des modèles de prévision destinés à être utilisés dans des systèmes d’alerte précoce, en vue d’atténuer les risques liés au climat, sont en outre développés. Les objectifs spécifiques de l’étude incluent : un diagnostic des différents aspects de la répartition des épisodes secs et pluvieux, dans leur variation interannuelle ; une analyse des relations entre les aspects de cette répartition ainsi identifiés et les principaux champs climatiques d’échelle large qui gouvernent le climat global ; une évaluation de la prévisibilité des différents aspects des épisodes secs et pluvieux pour l’amélioration des systèmes d’alerte précoce de la région.Plusieurs bases de données couvrant une période de 40 ans (1961-2000) ont été utilisées. Elles comprennent des séries de précipitations journalières mesurées par pluviomètre dans les trois pays d’Afrique orientale (Kenya, Ouganda, Tanzanie) ; les températures de surface marine (SST) du Hadley Centre ; des données de réanalyses et des stations de radiosondages de Nairobi (Kenya) et de Bangui (République Centrafricaine). Des indices d’El Niño-Oscillation Australe (ENSO), du Dipôle de l’Océan Indien et de gradients de SST, constituant des prédicteurs SST prédéfinis, ont été également utilisés [...] / Most of Eastern Africa has arid and semi-arid climate with high space-time variability in rainfall. The droughts are very common in this region, and often persist for several years, preceded or followed by extreme floods. Most of the livelihoods and socio-economic activities however remain rain-dependent leading to severe negative impacts during the periods of occurrence of climate extremes. It has been noted that one extreme event was capable of reversing national economic growth made over a period of several years. Thus no sustainable development can be attained in eastern Africa without effective mainstreaming of climate information in the development policies, plans and programmes. Many past studies in the region have focused on rainfall variability at seasonal, annual and decadal scales. Very little work has been done at intraseasonal timescale that is paramount to most agricultural applications. This study aims at filling this research gap, by investigating the structure of rainfall season in terms of the distribution of wet and dry spells and how this distribution varies in space and time at interannual time scale over Equatorial Eastern Africa. Prediction models for use in the early warning systems aimed at climate risk reduction were finally developed. The specific objectives of the study include, delineate and diagnose the some aspects of the distribution of the wet and dry spells at interannual timescale; investigate the linkages between the aspects of the distribution of wet and dry spells identified and dominant large scale climate fields that drive the global climate; and assess the predictability of the various aspects of wet and dry spells for the improvement of the use in the early warning systems of the region.Several datasets spanning a period of 40 years (1961 – 2000) were used. The data included gauged daily rainfall amount for the three Eastern Africa countries namely Kenya, Uganda, and Tanzania; Hadley Centre Sea Surface Temperature (SST); re-analysis data and radiosonde observations from Nairobi (Kenya) and Bangui (Central Africa Republic) upper air stations. The indices of El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole and SST gradients which constituted the predefined predictors were also used [...]

Smallholder farmers often have great entrepreneurial qualities that build on generations of experience. However, many farm management practices are poorly adapted to current climate change conditions. In order for farmers to understand the risks they are undertaking by following certain farming practices and to adapt accordingly, a decision support tool is being developed by researchers at TU Delft. The tool runs a socio-hydrological model, created in Python, in the back-end and provides farmer specific investment and profit data for different crops in the front-end. The aim of this study is to develop a risk assessment process that integrates hydro-climatic variability in the decision support tool, and to identify ways of communicating risk to smallholder farmers in Maharashtra, India. Two sources of variability were characterised based on a literature review of Indian farmers’ own risk perceptions; the untimely onset of the Indian Summer Monsoon and the frequency of dry spells. A sensitivity analysis was then carried out to investigate their respective effects on the farmers’ crop yields. The method proposed to evaluate these risks used a single variable, precipitation data, and a two-dimensional risk matrix to compound the two risk factors, over a time span of 14 years (2003-2016). However, the results indicate that it might be more beneficial to define dry spells in terms of crop water stress, instead of a precipitation threshold. This study also proposed a method for translating a cumulative distribution curve into a risk representation that is adapted for low-literacy users by combining numbers and text with graphics, color and voice descriptions. Ultimately, however, the usability of the tool cannot be determined solely through literature, but must involve the end-users in its design. / Småskaliga jordbrukare är goda entreprenörer som samlat på sig kunskaper och erfarenheter över flera generationer. Däremot är vissa metoder som jordbrukarna använder sig av idag för att förvalta sitt jordbruk inte anpassade till nutida klimatförändringar. För att jordbrukarna ska förstå riskerna som de åtar sig vid valet av dessa metoder försöker forskare vid TU Delft nu ta fram ett verktyg för att underlätta jordbrukares förmåga att ta självständiga men välgrundade beslut om sitt jordbruk. Verktyget är baserat på en socio-hydrologisk modell som är framtagen i Python och som förser specifika investerings- och inkomstdata för enskilda jordbrukare. Syftet med detta kandidatarbete är att bidra till verktyget genom att undersöka de hydroklimatiska risker som uppstår till följd av föränderliga och osäkra klimatologiska förhållanden för jordbrukare i delstaten Maharashtra, Indien. Två riskfaktorer karakteriserades baserat på en litteraturstudie om indiska jordbrukares riskuppfattningar: avvikelser i starten på den indiska sommarmonsunen och antal torrperioder under monsunsäsongen. Dessutom utfördes en känslighetsanalys för att undersöka om och hur den existerande modellens utdata av skörd påverkades av de valda riskfaktorerna. Monsunstarten och torrperioderna togs fram genom metoder som enbart använde historiska nederbördsdata över tidsperioden 2003-2016 och kombinerades sedan med hjälp av en tvådimensionell riskmatris. Resultaten visade att det fanns anledning att ifrågasätta hur torrperioderna definierades och att det kan vara mer fördelaktigt att undersöka vattenbrist för grödan, snarare än att enbart förlita sig på nederbördsdata. Vidare föreslog denna studie en metod för att översätta en kumulativ fördelningsfunktion till en grafisk riskframställning som är anpassad till användare med låg läskunnighet genom att kombinera siffror med text, grafik, färg och ljudförklaringar. I slutändan kan dock inte användbarheten av verktyget enbart avgöras utifrån litteratur, utan måste även inkludera återkoppling från slutanvändarna.