Simple modeling of the global variation in annual forest evapotranspiration

Annual forest evapotranspiration (ET) is highly variable among various sites. Zhang’s model () has been widely used for predicting the spatial variation in ET. The forest component of the model employs limiting theory and assumes constant annual potential evaporation (E0 = 1410 mm) by regressing data recorded at 56 forest sites. However, most of the data used in determining E0 were recorded for limited regions (Australia, African countries, and the United States). We summarized 829 forest ET data items obtained for sites around the world from earlier publications. Using the dataset, we showed that Zhang’s model overestimates forest ET in temperate and boreal regions with low annual mean temperature (T) owing to the E0 value. We revised the E0 term of Zhang’s model so as to consider the dependency of E0 on T using the dataset. The revised model did not overestimate forest ET in temperate and boreal regions. Consequently, we recommend revising the E0 term of Zhang’s model when predicting forest ET in these regions.