A Study On The Dynamic Process Of Evapotranspiration And Its Responses To Climate Change On The Tibetan Plateau

Land surface evapotranspiration is a vital part of terrestrial water balance and land surface energy exchange.Accurately quantifying terrestrial evapotranspiration is of great significance to predict hydroclimates and terrestrial water and carbon cycles.However,the limitations of the actual evapotranspiration observations on the Tibetan Plateau in terms of spatial representation and temporal coverage,as well as the uncertainty of soil and vegetation parameters in land surface model and remote sensing methods have hindered the reliable estimation of actual evapotranspiration.Therefore,the dynamic processes of the land surface evapotranspiration at different temporal and spatial scales were investigated using the in-situ observation and CR theoretical model approaches.We also analyzed the dominant environmental factor contributing to the annual evapotranspiration and its response to climate change.In this study,the observed site of Fenghuo Mountains in the permafrost regions of the Tibetan Plateau and the region of the entire Tibetan Plateau were selected as the research areas.The main results in this study are summarized here:?1?Based on the observation from eddy covariance of latent heat flux and sensible heat flux,there was an asymmetrical complementary relationship between the actual evapotranspiration and potential evapotranspiration of Fenghuo Mountains station on the Tibetan Plateau.The simulation results of daily evapotranspiration by generalized nonlinear complementary relationship?GCR?and the improved SGCR method expressed that the accuracy of estimation from SGCR method was improved compared with that from GCR,and the calibration-free feature of SGCR model provides a possible way to calculate the actual evapotranspiration on a regional scale.We also found that the seasonal variation of the energy flux of the Fenghuo Mountains site was related to the freezing and thawing process of the active layer and the rainfall affected by the Asian monsoon.?2?The monthly actual evapotranspiration over the entire Tibetan Plateau from1982 to 2015 were calculated using the latest rescaled SGCR with a spatial resolution of 0.1°from 1982 to 2015.The multi-year average evapotranspiration?1982-2015?was 373.12 mm yr^-1.Additionally,the analysis of the dominant environmental factor contributing to the annual evapotranspiration and its response to climate change showed that the key meteorological elements which affected annual evapotranspiration on the Tibetan Plateau were relative humidity and net radiation,and the analysis of net precipitation indicated that the regional atmosphere was becoming wetter during that34 years.This study hope to further improve the development and application of complementary relationships and better understand the hydrometeorology and terrestrial water-carbon cycle processes in the context of climate change.