Assessment of changes in land use and occupation on the hydrological regime of a basin in the west of Bahia

Abstract

The western region of Bahia is one of the most active agricultural frontiers in the country, where areas of vegetation have been replaced by agricultural areas, both rainfed and irrigated. These changes have resulted in conflicts over water use in the region, particularly in this study area, which corresponds to the Sítio Grande flow measurement point, representing a sub-basin of the Rio Grande. Although this scenario of conflicts and water unavailability is attributed to human actions, the decrease in water availability may also be associated with factors such as climate change. This constitutes the main aim of this study, which was to evaluate the hydrological responses to climate change and to land use and occupation using the SWAT hydrological model. The model was calibrated and validated for 3 different periods (1986–1990; 1991–1995), (1996–2000; 2001–2005), (2006–2010; 2011–2015), respectively. These periods were divided so as to portray the observed flow of the drainage basin as closely as possible, since over the years the use and occupation of the land have changed. The simulations were based on the fixing-changing method, in which the three periods were simulated for three different maps of land use and occupation (1990, 2005, and 2015), fixing the land use and occupation map and changing the simulation period. The results show that the SWAT performed satisfactorily in its analysis of the three periods studied on a monthly scale. The areas of all forest types of the Cerrado biome in this sub-basin were reduced by 27.47% between 1990 and 2015, while agricultural areas grew by 192.48%. Land use change scenarios indicate a reduction in flow. If the land use and occupation of the initial period of the study (1990) had remained unchanged and the natural vegetation had been preserved, the Q90, maximum, average, and minimum flows would be higher than in the current scenario.