Annual evapotranspiration estimates are crucial for managing water resources. Researchers tested 5 equations using climate data on 11 watersheds in Korea. The Schreiber formula works best in sub-humid regions, while the Zhang equation is more accurate in humid areas. Overall, the Zhang equation had the lowest bias in estimating evapotranspiration across the watersheds. These equations can help water managers estimate water resources in large watersheds without gauges.