<p>This study investigates historical and projected climate change in the Constantine Highlands watershed in northeastern Algeria. The historical analysis, based on the NASA POWER gridded dataset for the period 1990–2020, indicates a statistically significant warming trend, while precipitation exhibits a general but non-significant decreasing tendency across the study area. Future changes were assessed up to 2100 using an ensemble of regional climate models from the EURO-CORDEX initiative under two emission scenarios (RCP4.5 and RCP8.5). Climate model outputs were bias-corrected using reanalysis-based data from NASA POWER, and projections were analyzed over three future periods (2021–2040, 2041–2060, and 2076–2095). The results consistently indicate a marked warming across the study area, with stronger increases under the high-emission scenario. Precipitation projections suggest a general tendency toward decreasing annual totals, although with considerable variability among models and seasons. Reductions are more pronounced in spring and summer, pointing to a potential intensification of seasonal drying. Climate extreme indices (ETCCDI) further suggest an increase in consecutive dry days and a general reduction in seasonal precipitation totals. While some indices indicate a possible increase in rainfall intensity, this signal is not consistent across all models and periods, and should therefore be interpreted with caution. Overall, the results highlight a robust warming signal combined with a tendency toward drier conditions and longer dry spells, suggesting increasing vulnerability of the Constantine Highlands watershed to future climate change.</p>