Projected temperature and precipitation changes under future climate scenarios in the Siak watershed, Indonesia

Climate change is altering global temperature and precipitation regimes, with significant implications for hydrological systems. This study presents high-resolution projections of future temperature and rainfall for the Siak Watershed, Indonesia, using Coupled Model Intercomparison Project Phase 6 (CMIP6) outputs statistically downscaled with the Statistical Downscaling Model (SDSM). Downscaling is performed through a rigorous predictor-selection procedure to ensure physical consistency. Observed temperature records and Global Satellite Mapping of Precipitation (GSMaP) data for the current period (2003–2022) are used as the baseline, while projections are developed for three future periods (FPs)—2025–2050 (FP I), 2051–2075 (FP II), and 2076–2100 (FP III)—under Shared Socioeconomic Pathways (SSPs): SSP1-2.6, SSP2-4.5, and SSP5-8.5. Temporal trends are evaluated using the non-parametric Mann–Kendall test. Results show that predictor selection should combine statistical evaluation, ranking, and spatial analysis for consistency with natural conditions. Both temperature and rainfall are projected to increase, with temperature rising by up to 3.7% and rainfall by 26.8%, especially under SSP5–8.5. Adjustments to the predictor configuration effectively reduce the occurrence of Consecutive Dry Days (CDDs), indicating a tendency toward wetter future conditions. Nevertheless, the potential for heightened drought risk persists as a result of projected temperature increases. These findings provide a scientific basis for drought mitigation in northern Siak and flood risk management in southern Siak.