Shifting Patterns of Precipitation Extremes in the S outheast A tlantic Basin— B razil: From Observed Trends to Future Projections

Understanding the variability and evolution of precipitation extremes associated with climate change is essential to support adaptation strategies, risk management, and civil protection. In this context, this study investigates the climatology, observed trends, and future projections of precipitation extremes in the Southeast Atlantic Hydrographic Basin (SAHB), a region of great socioeconomic relevance in Brazil. Daily precipitation data from 244 pluviometric and meteorological stations of the National Water and Basic Sanitation Agency (ANA) and the National Institute of Meteorology (INMET) were used, covering the period from 1980 to 2023. Precipitation extremes were evaluated using standardized indices from the Expert Team on Climate Change Detection and Indices (ETCCDI). Trend detection and assessment in the time series were performed using the non‐parametric Mann–Kendall test and Sen's slope estimator. For the evaluation of future conditions, simulations from the EC‐Earth3 Earth system model, part of CMIP6, were used, considering the SSP2‐4.5 and SSP5‐8.5 emission scenarios for the period 2030–2100. The results indicate a significant increase in the mean rainfall intensity and a longer duration of dry periods (+4 days/decade), suggesting greater irregularity in the regional precipitation regime. Extreme precipitation events over short periods exhibit spatially heterogeneous intensification, with greater intensity in coastal and mountainous regions. Future projections indicate intensified extreme rainfall (up to +41 mm/decade in precipitation above the 95th percentile) and longer dry spells, particularly under the high‐emission scenario, suggesting greater susceptibility to hydrometeorological disasters and significant impacts on water security and territorial planning across the basin.