HYDROCLIMATIC VARIABILITY ON THE RIO NEGRO WATERSHED: A CASE STUDY AT BRAZILIAN AREA

In this article we carried out a hydroclimatological characterization of the upper reaches of the Rio Negro Basin, located in the Brazilian portion. We used rainfall and streamflow data from the Instituto Nacional de Meteorologia (INMET) and the Agencia Nacional de Aguas (ANA) in the 1995-2014 period, collected at different points surrounding the watershed. From the data analysis, we can identify that the average annual precipitation over the basin varies between 1440 and 1480mm. The annual average streamflow was approximately 538,7mm, corresponding to a runoff coefficient of 38%. The accumulated rainfall and streamflow series showed that, as of mid-year 2004, there was a significant reduction of the accumulated streamflow, probably caused by an increase in water demand for agricultural irrigation due to lower volumes of rainfall. Pre-2005 runoff coefficient showed an interannual oscillation between 36% and 42%, after 2005 the runoff coefficient systematically decreased from 45% to 35%. This reduction suggests an increase in the extraction of water for irrigation which consequently favors greater crop evapotranspiration in a period with slightly lower annual precipitation (2005-2014) compared to the previous period (1995-2004).