Groundwater storage projection in headwater basins under different climate conditions in Southeast Brazil

Abstract Groundwater resources in watersheds are rapidly depleting due to increased water use. In southeastern Brazil, droughts have intensified over the past 20 years, driven by changes in temperature and rainfall regimes. This study assessed groundwater in two headwater basins with contrasting climates in Minas Gerais State, namely the Grande and Jequitinhonha River basins, under climate warming scenarios to quantify potential impacts on water storage. The selection of these watersheds was intended to serve as a reference for potential future climate impacts in this region, given that human intervention in these watersheds was relatively low over the last 20 years. This study expands upon the findings from a previous study, which assessed groundwater storage behavior based on observed time series in the same river basins. The MHD-INPE hydrological model was used for simulations, with climate projections extending through 2099. Minimum annual groundwater storage was estimated using the Brutsaert method and baseflow simulations, and the Mann–Kendall test and Sen’s slope estimator were used to assess trends in groundwater storage. Our analysis revealed significant decreasing trends in groundwater storage in both watersheds. Compared with the baseline, reductions were observed in all projections, with the largest decline in the 2071–2099 projection under RCP 8.5 in the Grande River basin (74.4%), indicating that this basin may become less resilient to climate change over the century. These findings may support decision-making through water resources management tools, such as water allocation mechanisms, thereby helping mitigate impacts on the future.