Changes in Mean Annual Precipitation over the Brazilian and Nearby Regions from 1940 to 2099 Based on Weather Stations, Reanalyses, and the CMIP6 Model Ensemble

This study analyzes changes in precipitation over the extended Brazilian region (10° N–40° S; 75° W–25° W) based on data from meteorological stations, reanalyses (ECMWF ERA5, NASA MERRA-2), the NOAA PREC reconstruction, and an ensemble of 32 CMIP6 models. According to weather station data and the ERA5 reanalysis for the period 1996–2025, a slight decrease in mean precipitation (P) is observed in the whole region (ΔPWeather station = −44 mm/year, ΔPERA5 = −174 mm/year). A comparison of the periods 1996–2025 and 1940–1969 using CMIP6 ensemble also indicates a reduction in regional average precipitation (ΔPAve = −18 mm/year). The reanalyses show a decline in precipitation beginning approximately in the 1980s, accompanied by significant interannual and interdecadal variability associated with natural climate variability. Future projections under high radiative forcing scenarios (SSP3-7.0 and SSP5-8.5) indicate a continued decline in average precipitation in the study region throughout the 21st century. Low forcing scenarios (SSP1-2.6 and SSP2-4.5) suggest only weak changes in average precipitation over the period 2026–2099. However, the precipitation changes are spatially heterogeneous in the study region. According to the ERA5 reanalysis (1940–2025), precipitation has increased over the northern and southern parts of the Brazilian territory, while a decrease was observed in its central portion. All CMIP6 SSP ensemble projections considered (2026–2099) indicate a decrease in precipitation in the north and an increase in the south of the Brazilian region. Moreover, with increasing radiative forcing, the reduction in precipitation in the Amazon River basin and adjacent territories will intensify.