Análise de Tendência da Precipitação Diária na Amazônia Brasileira (Trend analysis of daily precipitation in the Brazilian Amazon)

O objetivo deste trabalho e avaliar as tendencias nas series temporais de precipitacao diaria em sub-regioes da Amazonia Brasileira. Para tanto, foram utilizados os dados diarios de precipitacao da rede hidrometeorologica gerenciada pela Agencia Nacional de Agua e do Banco de Dados Meteorologicos para Ensino e Pesquisa do Instituto Nacional de Meteorologia, para o periodo de 1983 a 2012. As sub-regioes da Amazonia foram representadas por series sinteticas, que consiste em usar os valores maximos diarios de cada sub-regiao. As tendencias foram calculadas atraves do teste nao parametrico de Mann-Kendall e da tecnica nao parametrica de suavizacao de LOWESS ( locally weighted regression scatter-plot smoothing ). Foram analisados os dias com precipitacao acima dos quantis 50% e 95%. Os resultados mostraram tendencias positivas e negativas, no entanto, nem todas as tendencias apresentaram significância estatistica. Foram encontradas tendencias significativas no aumento do numero de dias com precipitacao acima dos quantis 50% e 95% nas sub-regioes do noroeste da Amazonia. Ao mesmo tempo, houve diminuicao do numero de dias com precipitacao acima do quantil 95% em uma sub-regiao do sul da Amazonia. No metodo de LOWESS, tambem foi possivel verificar tendencias positivas no noroeste da Amazonia, sugerindo aumento de eventos de precipitacao intensa nessa regiao.  A B S T R A C T Extreme precipitation events have been causing great social and economic losses in the affected regions. In the Amazon, these events can have serious impacts, primarily for populations living on the margins of its countless rivers, because when water levels are elevated, floods and/or inundations are generally observed. Thus, t he objective of this study is to evaluate trends in the time series of daily precipitation into sub-regions of the Brazilian Amazon. The study was performed based on daily rainfall data of the hydrometeorological network managed by the National Water Agency ( Agencia Nacional de Agua ) and the Bank of Meteorological Data for Education and Research of the National Institute of Meteorology ( Instituto Nacional de Meteorologia ), from 1983-2012. Synthetic series to represent the homogeneous sub-regions were Created, which consists of using the daily maximum values of each sub-region. The trends were calculated using the Mann-Kendall test and the smoothing technique LOWESS ( locally weighted regression scatter-plot smoothing ) . Days with precipitation above the 50% and 95% quintiles were analyzed. The results showed positive and negative trends, however, not all trends were statistically significant. Significant trends were found in the increasing number of days with precipitation above the 50% and 95% quantiles in sub-regions of northwestern Amazonia. At the same time, there was a decrease in the number of days with precipitation above the 95% quantile in a sub-region of southern Amazonia. In LOWESS method, we could also verify positive trends in northwest Amazonia, suggesting an increase of intense precipitation events in this region. Key words: homogeneous rainfall regions, maximum precipitation, non parametric tests.