Evaluation of gridded precipitation datasets over Iran

Study region: Six climate zones in Iran: Zone 1 (humid Caspian region), Zone 2 (cold and semi-arid northwestern Iran), Zone 3 (mild and semi-humid western Iran), Zone 4 (mild and semi-arid northeastern Iran), Zone 5 (warm and semi-arid southwestern Iran), and Zone 6 (warm and arid eastern, southern, and southeastern Iran). Study focus: This study evaluates the performance of seven gridded precipitation datasets (CRU TS, TMPA 3B43, GPCC, IMERG, MERRA-2, ERA5, and PDIR) against rain gauge data. The accuracy of these datasets in representing precipitation patterns is assessed from 2000 to 2017, with a focus on their performance across diverse climate zones in Iran. New insights for the region: In Zone 1, ERA5 performs best in winter and autumn, while GPCC excels in spring and summer. In Zones 2 and 3, GPCC is the top performer in most seasons, while CRU TS performs best in autumn and winter for Zone 2. In Zone 4, GPCC outperforms all datasets year-round. In Zone 5, TMPA 3B43 performs best in winter, with GPCC slightly outperforming others in other seasons. Overall, ERA5 is most accurate in Zone 1, while GPCC performs best in other zones, with PDIR consistently underperforming across all zones. GPCC captures interannual precipitation variability well, making it the best overall performer. We recommend ERA5 for realtime monitoring in Zone 1, while GPCC is better suited for long-term studies in areas with dense rain gauge networks.