Evaporation From Soil and Thermokarst Lakes Contribute More to Local Precipitation Than Plant Transpiration in Permafrost Regions of the Central Qinghai—Tibet Plateau

Abstract Permafrost degradation on the Qinghai—Tibet Plateau (QTP) directly affects evapotranspiration and moisture recycling processes by changing the underlying land surface conditions. However, the contributions of thermokarst lake evaporation and plant transpiration to local precipitation in permafrost regions of the QTP remain unknown. In this study, precipitation, thermokarst lake water, plant, and soil samples were collected, and the proportional contributions of thermokarst lake evaporation, soil evaporation, and plant transpiration to local precipitation were quantitatively estimated via the Bayesian isotopic mixing model in permafrost region of the central QTP. The results revealed that the contribution of advected vapor to local precipitation was dominant, with a mean value of 74.6%, and the moisture recycling ratio ranged from 19.7 ± 2.1% to 29.7 ± 3.6% (mean: 25.4%). The mean contribution fractions of thermokarst lake evaporation and soil evaporation were 9.2% and 8.9%, respectively. In contrast to the findings of related studies in the nearby Qilian Mountains and arid Central Asian oases, the total surface evaporation contribution of 18.1% was considerably greater than the 7.4% contribution of plant transpiration in this study area. This discrepancy was primarily driven by extensive thermokarst lake coverage, sparse vegetation, and relatively high soil moisture conditions.