Freshwater scarcity poses a critical challenge in arid and semi-arid regions such as Iran, where evaporation from dam reservoirs contributes substantially to water loss. This study quantifies evaporation volumes from 117 major Iranian reservoirs using a combination of six empirical models and four satellite-based datasets (MODIS, GLDAS, SEBAL, and ERA5). Observational data from 339 synoptic stations were used to validate model performance using statistical indices (R-2 and RMSE). Among empirical models, Penman-Monteith achieved the highest accuracy (R(2)8 = 0.54, RMSE = 688 mm), while SEBAL and ERA5 demonstrated superior performance among satellite products (R-2 > 0.91, RMSE < 13 mm). Estimated annual evaporation volumes ranged from 2.2 to 2.8 billion cubic meters, with MODIS showing consistent underestimation. The highest evaporation losses were observed in southwestern and southeastern provinces, particularly Khuzestan and Sistan-Baluchestan, which face concurrent water scarcity. The findings emphasize the value of hybrid modeling approaches and satellite integration for national-scale hydrological assessments. This study provides a practical framework for improving water resource management and adapting to climatic variability in data-scarce environments.