Changes in land evapotranspiration under vegetation greening over the Arctic: Patterns, causes and temperature effects

Vegetation greening has been confirmed across the Arctic, which inevitably impacts the region’s water and energy cycles. Land evapotranspiration (ET), a critical component of these cycles, is influenced by vegetation dynamics and climate change, and it also provides feedback on the climate. However, the dominant factors influencing changes in land ET and its temperature effects remain unclear in the Arctic. In this study, we used the Bayesian-based regression method, geographical detectors, Extreme Gradient Boosting, SHapley Additive exPlanation, and empirical equations to comprehensively investigate the patterns, causes, and temperature effects of land ET changes during significant greening periods and across regions of the Arctic from 1982 to 2015. In terms of patterns, land ET showed a non-significant (p > 0.05) upward trend (0.39 mm/decade) in July and a significant (p < 0.001) downward trend (−0.88 mm/decade) in August. Spatially, in July, land ET exhibited a significant upward trend across western Alaska, Victoria Island, Nunavut, and western Yakutia. In August, land ET decreased across most significant greening regions, except for the Canadian Archipelago. Regarding causes, attribution analysis indicates that precipitation is the dominant factor determining the spatial pattern of land ET change trends across the Arctic. Additionally, increased precipitation and solar radiation positively contributed to the enhanced land ET in July, while the reduced land ET in August was primarily controlled by decreased precipitation. As for the temperature effects, ET process exerts an important cooling effect on the Arctic climate, particularly in the tundra wetlands, with a long-term average cooling effect of −0.27 °C in July, −0.20 °C in August, and −0.24 °C for the average of July and August across significant greening regions from 1982 to 2015. The findings of this study could improve our understanding of Arctic water cycle, thereby improving the prediction and assessment of Arctic water circulation under climate warming.