Evapotranspiration and energy partitioning of a typical alpine wetland in the central Tibetan Plateau

The alpine wetlands in the Tibetan Plateau (TP) account for more than 30% of the wetlands in China. As an ecosystem that is particularly sensitive to the changing climate, the rapid warming of the TP may have a significant impact on the growth of vegetation in these cold wetlands. However, due to the lack of ground observations, it remains unclear how the land-atmosphere exchanges of water and energy develop in such special alpine ecosystems. This limits the understanding of how eco-hydrological processes respond to environmental changes. In this study, we used ground measured data to investigate the dynamics of energy partitioning and water budget over a typical wetland in the central TP over two hydrological years. The results demonstrate that the seasonal variations in land-atmosphere energy exchange were significant during the observation period. In the growing season, the available energy was mainly consumed by latent heat flux (LE), with the mean ratio of LE to net radiation (R-n) exhibiting values of 0.68 and 0.76 in 2019 and 2020, respectively. During the freezing period, the available energy was primarily consumed by sensible heat flux (H), with mean ratio of H to R-n values of 0.69 and 0.68 in 2019 and 2020, respectively. The total annual evapotranspiration (ET) (include sublimation) in 2019 and 2020 were 652.5 mm and 706.6 mm, respectively. Annual ET was found to be higher than precipitation (P), indicating that soil water was supplied via lateral flow from the melting of upstream glaciers and snow, supporting ET from the wetland. During the growing season, ET was mainly controlled by solar radiation but became more strongly coupled with soil water during the freezing period. Evaluations of four typical gridded ET products suggest that the Penman-Monteith-Leuning (PML) model showed the best performance with the highest Nash-Sutcliffe Efficiency (NSE) when compared with the ground-measured ET rates, indicating that this product may be appropriate for use in similar data-scarce regions. The land-atmosphere energy and water exchanges in the alpine wetland are important for an improved understanding of the hydrological cycle of the Asian Water Tower and could be used as a reference for further ET model parameterizations and validations.