Role of permafrost degradation on evapotranspiration on the Qinghai-Tibet Plateau

The Qinghai-Tibet Plateau (QTP), known as the "Asian Water Tower", is extremely sensitive to climate change. Studying the impacts of permafrost degradation on evapotranspiration is conducive to improving the understanding of the response of hydrological processes and water balance to climate change in the QTP. Based on the Budyko-Fu hypothesis, a coupled hydrothermal model was constructed to account for the active layer deepening of the permafrost regions with a model parameterization scheme suitable for the QTP. The results show that the annual average evapotranspiration in the permafrost regions on the QTP is 275.6 mm during 1982—2018 and shows a descending gradient from southeast to northwest. The overall evapotranspiration in the permafrost areas on the QTP increased significantly at a rate of 3.57 mm/a (p < 0.05). Deepening of the active layer causes increased evapotranspiration while ignoring the permafrost degradation would result in an underestimation of evapotranspiration by about 2.2%. The effects of permafrost degradation on evapotranspiration exhibit a significant spatial heterogeneity. The lower the soil available water capacity and vegetation coverage are, the more sensitive the responses of evapotranspiration to permafrost degradation become.