Hydrological processes in a watershed on the transition from Amazon to Cerrado in Brazil

This study analyzed the spatial and temporal variability of hydrological processes of precipitation, evapotranspiration, discharge, water storage, runoff, and a dryness index in the Mearim River basin, in the Amazon-Cerrado transition in Brazil. Furthermore, we investigated whether the changes found are due to land use and land cover change (LULC) or climate and whether these changes are significant. We used the Large Basin Hydrological Model (MGB), which showed good or optimal performance for most sub-basins and periods. The study period comprised thirty-one years (1990–2020), subdivided into three analysis periods, according to the temporal dynamics of LULC in the basin. The temporal variability indicated increases of 7.3% in precipitation, 3.7% in AET, and 29.7% in mean discharge in the second period (2001–2010) compared to the first period (1990–2000), followed by a decline in the last (2011–2020) period: 6.6% for precipitation, 5.6% for AET and 12.7% for discharge. In the seasonal analysis, it was possible to identify that in the dry period, evapotranspiration and discharge are sustained by soil water storage, and it is still observed an 86.5% reduction in precipitation between the wet and dry seasons is also observed. Statistical evidence reveals that changes in hydrological variables are insignificant and that there are no trends of increase or decrease in the amount of water in the basin. Even with the strong dynamics of LULC, there are no significant effects on the discharge, which leads us to believe that the basin climate controls temporal changes in the PMIM hydrological processes.