Simulation of evapotranspiration based on leaf area index, precipitation and pan evaporation: A case study of Poyang Lake watershed, China

Abstract

Evapotranspiration (ET) is a major component of land hydrological processes, where it determines the transfer of moisture and energy in the soil–vegetation–atmosphere system. In this study, an empirical ET model (PYH-ET) was established based on the relationships between the monthly ET and the leaf area index (LAI), precipitation (PRE), and pan evaporation (EVP) in the whole Poyang Lake watershed (China). Then, this model was applied to sub-watersheds of the Poyang Lake watershed and analyzed the contributions of the three variables to ET. The results showed that the correlation coefficients between the monthly ET and the monthly LAI, PRE, and EVP were 0.969, 0.380, and 0.894, respectively. The moving average of the PRE per 2 months was used to replace the monthly PRE as a variable in the model. The accuracy of the PHY-ET model was high where the R value for the model was 0.98 and the relative error of the model was 10.2% when the data of 2014 were used to validate the model built according to the data during 2000–2013. The contribution of LAI to ET was highest in all sub-watersheds, followed by EVP, whereas PRE made the lowest contribution. In addition, the contributions of these three factors to ET in this watershed conformed to the law of the minimum, where the variation in ET was limited by the factor with the smallest change. The proposed high accuracy empirical model requires a small number of readily available parameters and it is suitable for integration with hydrological models.