CMIP6 GSMs Evaluation in the region of Cagayan River Basin.

General circulation model (GCM) projections from CMIP6 (Coupled Model Intercomparison Project Phase 6) were used to assess future rainfall conditions. The NEX-GDDP-CMIP6 (NASA Earth Exchange Global Daily Downscaled Climate Projections) dataset includes downscaled daily outputs from 34 GCMs over land regions with the resolution of 0.25 degree. GCMs are known to have substantial uncertainties, particularly at the regional scale. The evaluation compared GCM outputs against observational and reanalysis data across multiple climate variables, including precipitation (pr), near-surface air temperature (tas), surface downwelling longwave radiation (rlds), and surface wind speed (sfcWind). Observation dataset are bias corrected GSMaP for pr and ER5 for remainings.Each variable was assessed over selected grid cells within and around the Cagayan River Basin, as shown in below figure, based on their relevance to regional precipitation mechanisms. Model performance was evaluated for the historical period (1996–2015) using spatial correlation coefficients (Scorr) and root mean square error (RMSE). This multivariable comparison enabled the identification of GCMs that provide the most reliable precipitation projections for the region.