Terrestrial Evapotranspiration over China from 1982 to 2020: Consistency of Multiple Data Sets and Impact of Input Data

Due to limited direct measurements, regional or global terrestrial evapotranspiration (ET) is generally derived from a combination of meteorological and satellite observations. Although the inhomogeneity of the observed climate data has been widely reported, its impact on the calculated ET has not been adequately quantified. This study aimed to calculate ET using the modified Penman-Monteith (MPM) model with raw and homogenized meteorological data. Additionally, we compared the calculated ET with those estimates from variable methods (water balance, satellite-based, and reanalysis) in China and its six major river basins from 1982 to 2020. During the overlapping period of 1997-2018, ET calculated from raw input data decreased slightly at -0.39 mm yr-2 (p = 0.64) in China, whereas homogenized ET showed a significant increasing trend of 0.93 mm yr-2 (p = 0.02), with a better agreement with water balance ET (1.93 mm yr-2, p = 0). Global Land Evaporation Amsterdam Model (GLEAM) and Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA2) could reproduce the increasing trends with 2.08 mm yr-2 (p = 0) and 2.59 mm yr-2 (p = 0). The intercomparison of input variables (solar radiation, relative humidity, wind speed, precipitation, and air temperature) among ET products revealed substantial differences, which can account for the discrepancies in ET estimates. Homogenized ET, GLEAM and MERRA2 exhibited significant increasing trends in China and most river basins from 1982 to 2020. Our findings underscore the importance of utilizing homogenized input data for more accurate ET estimation. Regional or global terrestrial evapotranspiration (ET) is generally derived from a combination of meteorological and satellite observations. Previous studies have highlighted inhomogeneity issues in meteorological observations in China, which can introduce uncertainty to the ET estimated. However, the uncertainty of ET estimates has not been quantified. In this study, we recalculated ET in China using an energy partition model with raw and homogenized meteorological inputs from 1982 to 2020. We also compared ET estimates obtained from different methods (water balance, satellite-based, and reanalysis) to analyze trends in China and its major river basins over the same period. The study revealed that inhomogeneity in the input data distorted the calculated trends of ET. Calculated China's ET using raw and homogenized data in the modified Penman-Monteith model Improved ET trend with homogenized data, aligning better with water balance ET over China Homogenized ET exhibits a significant increasing trend of 0.90 mm yr-2 (p = 0) from 1982 to 2020 across China