ABSTRACT The objective of this study is to evaluate spatial and temporal variations in rainfall aggressiveness in southern Brazil. A total of 181 rain gauge stations located in southern Brazil with rainfall time series from 1976 to 2015 were used. Seasonal and annual rainfall aggressiveness values measured according to the Modified Fournier Index (MFI) were analyzed. The trends in the data series were evaluated using the Mann-Kendall test at a level of significance of 5%. Maps on spatial and seasonal variations in rainfall aggressiveness were prepared. The percentage of rain gauge stations with significant decreasing trends, significant increasing trends, and no significant trends in rainfall aggressiveness between years was 3.3%, 7.7%, and 89.0%, respectively. Moreover, 90% of stations had no significant trends between seasons. There were seasonal differences in rainfall aggressiveness between the three southern states in Brazil caused by rainfall factors. Rainfall aggressiveness was comparatively higher in the west of Santa Catarina and southwest of Paraná due to the rains originating from the mesoscale convective systems predominant in autumn, and in the north coast of Santa Catarina and east coast of Paraná due to convective and orographic precipitations predominant in the summer.

A distribuição da precipitação tem grande influência na produção agrícola e na economia da região Sul do Brasil. Este estudo teve como objetivo avaliar a distribuição espacial e sazonal e as tendências nas séries de precipitação da região Sul do Brasil. Para o efeito, foram utilizados dados de 197 estações pluviométricas localizadas na Região Sul do Brasil, que apresentaram mais de 32 anos de dados nas séries anuais no período de 1976 a 2015. Foram determinadas as séries anual e sazonal de precipitação e do Índice de Concentração da Precipitação (ICP). A tendência nas séries consideradas foi avaliada pelo teste de Mann-Kendall ao nível de significância de 5%. Foram apresentados os mapas evidenciando a variação espacial e sazonal tanto da precipitação quanto do ICP. Os resultados demonstram que as séries podem ser consideradas estacionárias, visto que mais de 83% das estações pluviométricas não apresentaram tendências significativas de aumento ou de redução no volume de precipitação, nem na concentração de chuva sobre a região em estudo. Em termos de sazonalidade da precipitação, também não ocorreram aí tendências significativas, embora fossem detetadas algumas variações sazonais e espaciais, de modo que no verão há maior número de estações que apresentam tendências de aumento da precipitação, sendo que no outono a tendência é de redução.

The precipitation distribution has a great influence on the agricultural production and economy of the southern region of Brazil. This study aimed to evaluate the spatial and seasonal distribution and trends in the precipitation series of the southern region of Brazil. For this purpose, we used data from 197 rain gauges located in the Southern Region of Brazil, which presented more than 32 years of data in the annual series from 1976 to 2015. The annual and seasonal precipitation series and the Precipitation Concentration Index (PCI) were obtained. The trend in the series was evaluated by the Mann-Kendall test at a significance level of 5%. The maps showing the spatial and seasonal variation of both precipitation and PCI were presented. The results show that the series can be considered stationary, since more than 83% of the rainfall stations did not present significant trends of increase or reduction in the volume of precipitation nor in the concentration of rain on the region under study. In terms of seasonality of precipitation, there were also no significant trends there, although some seasonal and spatial variations were detected, so that in summer there is a greater number of seasons that show increasing precipitation trends, and in autumn the tendency is for reduction.