Hydrological responses to climate and land use change in the Paraopeba River Basin, Southeastern Brazil: a Budyko framework spatial approach

The Paraopeba River Basin, in Southeastern Brazil, plays a strategic role in public water supply and economic activities in the Metropolitan Region of Belo Horizonte, the third most populous in the country, and has undergone marked environmental changes in recent decades. In this study, the relative contributions of climate and land use and land cover changes (LULC) to variations in water availability were quantified across five nested sub-basins over the period 1986 to 2022. The Budyko framework, a simple and effective tool for estimating the long-term water balance through the relationship between the evaporative and aridity indices, was applied to each sub-basin using the formulation of Fu (1981). Runoff changes were decomposed into direct climatic, indirect climatic, and anthropogenic components, based on 10-year moving averages. The aridity index showed an increasing trend in three of the five sub-basins. By 2022, all sub-basins exhibited reduced streamflow, with the largest decline occurring in the most downstream sub-basin, of 57.31% in relation to the long-term average, in response to climatic influence combined with agricultural expansion and irrigation withdrawals. In most of the basin, the negative effects of climate were partially offset by anthropogenic effects in the opposite direction. Overall, our findings point to increased regional water vulnerability and pronounced spatial heterogeneity in hydrological impacts.