Conversion features of evapotranspiration responding to climate warming in transitional climate regions in northern China

Abstract

Global surface evapotranspiration is one of the most significant components of the response of the water cycle to a warming climate. However, trends in surface evapotranspiration differ considerably from the trend in climate warming according to recent studies, with some studies even showing an opposing trend. The reason for this difference in the response of surface evapotranspiration to climate warming is still not completely understood. We validated the gridded FLUXNET evapotranspiration dataset and the Global Land Surface Assimilation Dataset (GLDAS) against evapotranspiration data observed in northern China using the eddy covariance system. The response of surface evapotranspiration to an increase in temperature varied with the type of climate (classified by the amount of precipitation) and the trend of surface evapotranspiration with warming showed similar features to the transitions between these climate types. The climate type with precipitation in the range of 250–350 mm was the most sensitive to the effects of warming on evapotranspiration. In more humid climates, surface evapotranspiration increased with increasing temperature, whereas in drier climates surface evapotranspiration decreased with increasing temperature. A similar response of evapotranspiration to increasing temperatures was also observed elsewhere in regions of climate transition. There are two main mechanisms of evapotranspiration: (1) an increase in temperature resulting in a direct increase in potential evapotranspiration; and (2) an increase in temperature resulting in a loss of soil moisture due to the increase in evapotranspiration, which in turn will indirectly suppress surface evapotranspiration due to the loss of vegetation.