Responses of global terrestrial evapotranspiration to climate change and increasing atmospheric CO₂ in the 21st century

Quantifying the spatial and temporal patterns of the water lost to the atmosphere through land surface evapotranspiration (ET) is essential for understanding the global hydrological cycle, but remains much uncertain. In this study, we use the Dynamic Land Ecosystem Model to estimate the global terrestrial ET during 2000-2009 and project its changes in response to climate change and increasing atmospheric CO₂ under two IPCC SRES scenarios (A2 and B1) during 2010-2099. Modeled results show a mean annual global terrestrial ET of about 549 (545-552) mm yr^-1 during 2000-2009. Relative to the 2000s, global terrestrial ET for the 2090s would increase by 30.7 mm yr^-1 (5.6%) and 13.2 mm yr^-1 (2.4%) under the A2 and B1 scenarios, respectively. About 60% of global land area would experience increasing ET at rates of over 9.5 mm decade^-1 over the study period under the A2 scenario. The Arctic region would have the largest ET increase (16% compared with the 2000s level) due to larger increase in temperature than other regions. Decreased ET would mainly take place in regions like central and western Asia, northern Africa, Australia, eastern South America, and Greenland due to declines in soil moisture and changing rainfall patterns. Our results indicate that warming temperature and increasing precipitation would result in large increase in ET by the end of the 21st century, while increasing atmospheric CO₂ would be responsible for decrease in ET, given the reduction of stomatal conductance under elevated CO₂.