Anthropogenic Influences Alter the Response and Seasonality of Evapotranspiration: A Case Study Over Two High Mountain Asia Basins

Earth's vegetation has been increasing over the past decades, altering water and energy cycles by changing evapotranspiration (ET). Greening, caused by climatic and anthropogenic factors, has high rates in High Mountain Asia (HMA). Here we focus on two HMA basins (the Yangtze and the Ganges-Brahmaputra) to contrast the impacts of climate- and human-induced greening on ET. Though the rate of greening is similar in both basins, anthropogenic influences lead to dissimilar responses in ET. In the Yangtze, climate-induced greening increases ET, with the increase in moisture being high enough to meet the ET demand. In the Ganges-Brahmaputra, irrigation-induced greening does not alter annual ET, only pre-monsoon ET increases. The dry season declines in water storage due to pumping decrease ET, while laboriously meeting the demand. This study provides a representative example of the contrasting influences of climate induced and anthropogenic driven processes on the seasonality of ET. The significant increases in vegetation occurring on Earth are susceptible to altering the climate by affecting evapotranspiration. However, the responses in evapotranspiration to the changes in vegetation depend on the drivers of greening. Here we use High Mountain Asia as a testbed to contrast the impacts of greening on evapotranspiration. Irrigation-induced greening leads to an increase in transpiration and evapotranspiration in the pre-monsoon. However, because irrigation decreases water storage it decreases evapotranspiration in the post-monsoon. Climate-induced greening, on the contrary, increases both evapotranspiration and water storage. Climate and human induced greening have different effects on evapotranspiration and therefore the land-atmosphere interactionsThough irrigation-induced greening rises pre-monsoon evapotranspiration, the latter decreases in post-monsoon due to groundwater depletionClimate-induced greening increases evapotranspiration because the energy demand is easily met