Climatological and hydrological patterns and verified trends in precipitation and streamflow in the basins of Brazilian hydroelectric plants

This study focuses on investigating possible changes in hydrometeorological behavior on important Brazilian river basins for power generation purposes. Thereby, this research analyzes the historical averages and observed trends regarding rainfall and streamflow and their impact on the hydrological regime. Ten river basins were selected for the assessment of alterations in the precipitation and streamflow series throughout descriptive measures and statistical significance tests (Mann-Kendall and Sen's slope). These data are available over different time spans, but most of the records include information from 1961 to 2006. As long as these river basins are subjected to different climate types, their corresponding rainfall and streamflow patterns vary accordingly the basin location in the country, in addition to the season. Most of the country has a predominantly tropical climate, with a wet period concentrated between October and March and a dry period between April and September. Some exceptions are the Northeastern region, where the climate is semi-arid, besides the Southern region, where there is abundant precipitation throughout the year. According to the obtained results, it could be noted that the streamflow response to precipitation is faster in the smaller river basins, what can be due especially to the water travel time. It was found that Belo Monte basin, in Northern Brazil, presents a statistically significant reduction in the annual rainfall. Furthermore, a significant decrease in the annual streamflow was also identified in Xingo and Sobradinho basins, in the Northeastern region. In contrast, Itaipu basin, located in Southern Brazil, showed increasing statistically significant trends in annual rainfall and streamflow during the second half of the twentieth century. Relevant decreasing trends were also identified in the minimum streamflows of the Brazilian Northern and Northeastern basins and increasing ones in the maximum streamflows in the Southern region basins. The results obtained in this work will support the assessment of the impact of rainfall and streamflow future scenarios in regulating capacity of the hydroelectric power plant reservoirs.