Evapotranspiration dynamics over a temperate meadow ecosystem in eastern Inner Mongolia, China

Ecosystem evapotranspiration links surface energy and water balance, which is very important to the forming and evolution of regional climate. To understand the evapotranspiration dynamic over the temperate meadow in Inner Mongolia grassland, a long-term continuous measurement of water vapour flux was conducted using eddy covariance technique from 2008 to 2013. The results showed that the seasonal variation of daily evapotranspiration displayed a unimodal pattern with maximum value of 6.45 mm day⁻¹. The mean value of annual evapotranspiration (ET) was 650 mm with 72 % occurring during the growing season from May to September. The annual evapotranspiration was larger than the annual precipitation (P), while less than the annual evaporation (E). The ET/P reached up to 1.91, while the ET/E was only 0.60. The evapotranspiration was not limited by precipitation due to additional water supply from surrounding dunes. The daily evapotranspiration was mainly driven by atmospheric moisture demand in the growing season with high Priestley–Taylor parameter, averaged 1.04. The daily evapotranspiration presented positive correlation with net radiation, and the correlation was affected by water vapour pressure deficit. The net radiation and water vapour pressure deficit controlled the evapotranspiration process together. The study site had the largest annual evapotranspiration and ET/P compared with the other ecosystems along the transection of Northeast China Transect, International Geosphere Biosphere Programme. The harvest activity could increase the albedo and then decrease the available energy of the surface, eventually reducing the monthly evapotranspiration as much as 33.98 % in September.