Vegetation greening and climate change promote an increase in evapotranspiration across Siberia

The greening of the Arctic and pan-Arctic regions in recent decades has been widely confirmed, while the details regarding the greening feedback effects involving the water and energy cycles are still vague. Evapotranspiration (ET), a vital process in the water and energy cycles, strongly corresponds to vegetation activities. Hence, in this study, we chose Siberia as the study area and, based on the Penman-Monteith-Leuning (PML) model, revealed the contribution of greening to ET. Moreover, the effects of the water vapour pressure deficit, surface net radiation (Rn) and wind speed (Um) on ET were evaluated. The results indicated that from 2000 to 2020, the annual ET in Siberia was 248.2 +/- 94.1 mm, and the trend was 0.54 +/- 1.38 mm/a. Greening was the major driver of ET variations; its contribution was 0.79 +/- 0.76 mm/a, and its relative contribution was 37%. Among the other analysed climate factors, ET was sensitive to R-n and U-m these factors contributed 0.51 +/- 0.85 mm/a and -0.38 +/- 0.54 mm/a, respectively, to ET variation, and their relative contributions were 33% and 19%, respectively. The effect of the water vapour pressure deficit was slight (0.29 +/- 0.22 mm/a, 11%), indicating that ET was hardly constrained by the water supply in Siberia. These results quantify the importance of greening on ET variations and highlight the important effects of R-n and U-m on ET in cold region terrestrial ecosystems. Furthermore, this study improves our understanding of the mechanism by which evapotranspiration varies and is valuable for predicting and evaluating the Arctic water cycle in "Arctic amplification".;