Long-term variations in actual evapotranspiration over the Tibetan Plateau

Actual terrestrial evapotranspiration (ETa) is a key parameter controlling land-atmosphere interaction processes and water cycle. However, spatial distribution and temporal changes in ETa over the Tibetan Plateau (TP) remain very uncertain. Here we estimate the multiyear (2001-2018) monthly ETa 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 14.5mm per month and correlation coefficients exceeding 0.9. The domain mean of annual ETa on the TP decreased slightly (-1.45 mm yr(-1), p < 0.05) from 2001 to 2018. The annual ETa increased significantly at a rate of 2.62 mm yr(-1) ( p < 0.05) in the eastern sector of the TP (long > 90 degrees 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 degrees E). In addition, the decreases in annual ETa were pronounced in the spring and summer seasons, while almost no trends were detected in the autumn and winter seasons. The mean annual ETa during 2001-2018 and over the whole TP was 496 +/- 23 mm. Thus, the total evapotranspiration from the terrestrial surface of the TP was 1238.3 +/- 57.6 km(3) yr(-1). The estimated ETa product presented in this study is useful for an improved understanding of changes in energy and water cycle on the TP.

Automated summary

This study estimated multiyear (2001-2018) monthly ETa and its spatial distribution on the Tibetan Plateau (TP) using meteorological data and satellite products. Results showed a significant increase in annual ETa in the eastern sector of the TP and a decrease in the western sector, with pronounced decreases in spring and summer seasons. The estimated ETa product provides useful insights into changes in energy and water cycle on the TP.