Long-term changes in evapotranspiration over China and attribution to climatic drivers during 1980–2010

Evapotranspiration (ET) is one of the most important variables in terrestrial ecosystems, linking the carbon-water-energy cycles. In this study, we first analyze the spatial patterns of annual ET changes during 1980–2010 across China using four ET products: (i) the Global Land Evaporation Amsterdam Model version 3.0a (GLEAMv3.0), (ii) the EartH2Observe ensemble (EartH2Observe-En), (iii) the Global Land Data Assimilation System version 2.0 with Noah model (GLDAS2.0-Noah), and (iv) the Modern Era Retrospective-Analysis for Research and Application-Land (MERRA-Land). The results show that the spatial distribution of annual mean ET values and long-term changes derived from these four ET products are similar. Overall, large-scale increases in ET are observed in southeastern China, while decreases in ET over the northeast. Furthermore, we apply a newly developed separation method with the Budyko framework to quantify the individual contribution of five climatic factors to ET changes, including precipitation (P), net radiation (Rn), air temperature (T), vapour pressure deficit (VPD), and wind speed (u). It is found that the dynamics of P, Rn, and VPD are all strongly correlated with ET, suggesting that they are the major climatic factors influencing ET changes. Specifically, precipitation is the dominant factor for ET in water-limited regions, while ET changes in energy-limited regions are dominated by VPD according to all ET products except the EartH2Observe-En in which Rn and VPD have comparable performance. Our study highlights the importance of VPD in ET changes across energy-limited regions of China and suggests that the role of VPD in land surface-atmosphere interactions should be considered in future studies.