Attributing the Variations in Evapotranspiration and Its Components of Alpine Grasslands Over the Tibetan Plateau

Abstract Clarifying the controlling factors of annual variations in evapotranspiration (ET) and its components (transpiration (T) and evaporation (E)) over alpine grasslands of high‐cold regions is vital to understanding the hydrological processes of the terrestrial ecosystem. Therefore, this study investigated the variability of ET and its components over the alpine grasslands of the Tibetan Plateau (TP) and the driving factors underlying these changes during 1961–2013. The results showed that the annual ET over alpine grasslands was 339 mm, of which 59% and 41% were contributed by E and T, respectively. Annual ET, E, and T over the TP grasslands changed insignificantly before 1995, whereas increased dramatically during 1995–2013. Regarding different alpine grassland types, annual ET and its components in seasonal frost regions (SAG) were larger than in permafrost regions (PAG). The increase of ET and its components in PAG was profoundly larger than that in the SAG region during 1995–2013. Water and energy factors controlled the ET of approximately 65% and 31% area of the TP grasslands, respectively. Leaf area index was the major cause of T variability throughout 64% area of TP grasslands, while regions where energy factors were the major force of T change were mainly located in the eastern SAG region. Variability of E on entire TP grasslands (81%) was mainly regulated by available water supply. Our results indicate that as permafrost degradation has the potential to amplify climate warming and precipitation increase, ET over the PAG region was expected to continue increasing faster than the SAG region.