Evaluating climate change shifts on water resources and sediment yield in a subtropical river basin in southeastern Brazil

Climate change presents a significant global challenge impacting hydrological and sedimentary processes across diverse landscapes. In São Paulo State, Brazil, projections indicate seasonal and spatial asymmetries in water availability, with heightened flood risks in some areas and reduced supply in others. This study assesses these impacts in the Mogi-Guaçu River basin, an essential fluvial system in southeastern Brazil, by integrating climate projections with hydrological and sediment modeling. The Soil and Water Assessment Tool (SWAT+) model was applied to simulate baseline conditions and future scenarios (SSP4.5 and SSP8.5) across three periods (2020 to 2046, 2047 to 2073, and 2074 to 2100). Comparative analysis of climate scenarios suggests that SSP4.5 will lead to moderate declines in water yield and streamflow anomalies, intensifying toward the century’s end (∼–25%). The high-emission SSP8.5 scenario forecasts more severe reductions, exceeding –30% by 2074 to 2100, with greater variability in seasonal hydrological patterns. Results indicate that decreasing precipitation trends, particularly after 2050, will significantly impact streamflow and baseflow. Monthly variations suggest intensified seasonal discrepancies, affecting both ecosystem stability and human water availability. Model performance evaluated using Nash-Sutcliffe Efficiency (NSE) values confirmed SWAT+’s reliability in simulating streamflow under diverse conditions. Daily NSE values ranged from 0.31 to 0.70, while monthly NSE reached up to 0.84, indicating good to very good agreement with observed data at most stations. Additionally, sediment yield projections highlight increasing flow irregularity, especially during winter months, potentially exacerbating soil erosion and sediment transport. These changes directly influence river morphodynamics, landscape evolution, and watershed management strategies. Our findings emphasize the vulnerability of subtropical river basins to climate-induced hydrological shifts, underscoring the necessity of adaptive water management and soil conservation policies. By integrating climate modeling with hydrological assessments, this study provides a framework for evaluating uncertainties in climate projections and their implications for sedimentary systems. The observed changes in streamflow and sediment yield present challenges for maintaining water security and mitigating land degradation in climate-sensitive regions. Ultimately, this research enhances understanding of climate-driven alterations in fluvial processes, offering valuable insights for policymakers, environmental planners, and researchers aiming to develop resilient watershed management strategies in response to climate change.