Long-term variations in actual evapotranspiration over the Tibetan Plateau

Actual terrestrial evapotranspiration (ET$_{a}$) is a key parameter controlling land–atmosphere interaction processes and water cycle. However, spatial distribution and temporal changes in ET$_{a}$ over the Tibetan Plateau (TP) remain very uncertain. Here we estimate the multiyear (2001–2018) monthly ET$_{a}$ and its spatial distribution on the TP by a combination of meteorological data and satellite products. Validation against data from six eddy-covariance monitoring sites yielded root-mean-square errors ranging from 9.3 to 14.5 mm per month and correlation coefficients exceeding 0.9. The domain mean of annual ET$_{a}$ on the TP decreased slightly (−1.45 mm yr$^{-1}$, p<0.05) from 2001 to 2018. The annual ET$_{a}$ increased significantly at a rate of 2.62 mm yr$^{-1}$ (p<0.05) in the eastern sector of the TP (long >90° E) but decreased significantly at a rate of −5.52 mm yr$^{-1}$ (p<0.05) in the western sector of the TP (long <90° E). In addition, the decreases in annual ET$_{a}$ were pronounced in the spring and summer seasons, while almost no trends were detected in the autumn and winter seasons. The mean annual ET$_{a}$ during 2001–2018 and over the whole TP was 496±23 mm. ... mehrThus, the total evapotranspiration from the terrestrial surface of the TP was 1238.3±57.6 km3 yr$^{-1}$. The estimated ET$_{a}$ product presented in this study is useful for an improved understanding of changes in energy and water cycle on the TP. The dataset is freely available at the Science Data Bank (https://doi.org/10.11922/sciencedb.t00000.00010; Han et al., 2020b) and at the National Tibetan Plateau Data Center (https://doi.org/10.11888/Hydro.tpdc.270995, Han et al., 2020a).