Cleber Assis dos Santos

Variability of rainfall and the rice production in Branco River basin

O rio Branco e o principal afluente do rio Negro e representa o tributario mais importante da margem esquerda da bacia do rio Amazonas. Seu territorio e coincidente com o Estado de Roraima, o que amplia sua importância hidrica e economica. Para analisar a variabilidade da precipitacao e sua relacao com a producao de arroz na bacia do rio Branco, foram utilizados dados de 20 estacoes pluviometricas e dados da producao de arroz, ambos no periodo de 2001 a 2010. A precipitacao media da bacia foi determinada pelo metodo de Thiessen (mensal e anual) e relacionada com a producao de arroz usando correlacao linear simples. A variabilidade temporal da precipitacao foi feita atraves de analises estatisticas (desvio padrao, maximos e minimos, mediana, quartis, aglomeracao hierarquica). A distribuicao espacial da precipitacao mostra um comportamento crescente de NE para SW, com a zona de maior producao de arroz coincidente com os minimos de precipitacao. A variabilidade entre o periodo mais e menos chuvoso e significativa e pode ocasionar uma sensivel reducao da entrada de agua pela precipitacao nas bacias dos rios Uraricoera e Tacutu que compoem o alto rio Branco. A variabilidade interanual das chuvas na regiao esta associada a ocorrencia dos fenomenos de El Nino/La Nina que provocam diminuicao/aumento da chuva na bacia. A variacao da producao anual de arroz tem relacao com essas oscilacoes, porem os efeitos do aumento/diminuicao da area plantada e a curta serie de dados adotada nao permitem uma correlacao mais direta. Abstract The Branco River is the main tributary of the Negro River, that is the most important tributary of the Amazon River, in the left bank. Its territory coincides with the State of Roraima , which increases their hydrical and economic importance. This purpose of this work was to analyze the variability of precipitation and its relation to rice production in the Branco River basin, with database of 20 rainfall stations and rice production, both from 2001 to 2010. The average of rainfall was determined by Thiessen method (monthly and annual), and related to rice production using simple linear correlation. The temporal variability of precipitation was evaluated by statistical analysis (standard deviation, maximum and minimum, median, quartiles, hierarchical clustering). The spatial distribution of precipitation shows an increasing pattern of NE to SW, where the area of higher production of rice coincides with the minimum of precipitation. The variability between the more and less rainy period is significant and can lead to a significant reduction of the input water by precipitation in the basins of rivers of Uraricoera and Tacutu in the upper Branco River. The inter-annual variability of rainfall in the region is associated with the occurrence of the phenomena of El Nino/La Nina causing decreased/increased rainfall in the basin. The variation of annual rice production is related to these fluctuations, but the effects of the increase/decrease in planted area and a short series of data adopted do not allow a more direct correlation.