Hydrological analysis of Rio Grande Basin (Bahia State) time series: contribu-tion of Urucuia Aquifer System

Abstract

The analysis of baseflow variation combined with the precipitation in a time series allows for inferences about the effects of climate change and groundwater exploitation. Considering the importance of Urucuia Aquifer System, which represents a strategic water source in Western Bahia, Northeastern Brazil, we proceeded to study the influence of this aquifer in the flow rate of the Rio Grande basin, located on the left bank of the São Francisco river. We used time series of flow rates and precipitation data from 1977 to 2013 and the methods of hydrographs separation were fixed range, sliding interval, local minimum and smoothed minima. The results demonstrate that the baseflow corresponds to the main component of the rivers flow rate contributing with 81.75% to 93.06%. The correlation between precipitation and baseflow trends shows that the baseflow decreasing is related to the fall of precipitation rates. However, the rate of baseflow decreasing (0.75% a 3.04% per year) is severer than the rate of precipitation (0.07% a 0.88% per year), thus indicating that other factors such as over-exploitation of the aquifer are responsible for the fall of the Rio Grande baseflow over time.