Environmental controls on evapotranspiration from sparse grassland in Mongolia

Abstract

AbstractEnvironmental controls on evapotranspiration were investigated at a sparse grassland in Mongolia during 2003 and 2004. The study site was located on the southern periphery of the Eurasian cryosphere. Data from Eddy covariance, aerodynamic, and manual measurements were used in the analysis. A decoupling factor (Ω) was calculated to determine the relative importance of surface conductance and radiation to change in evapotranspiration rates. Higher evapotranspiration rates associated with a higher frequency of large Ω values revealed the importance of radiation forcing on evapotranspiration at this study site. As Ω increases', the aerodynamic conductance (ga) increased correspondingly but vegetation conductance (gC) decreased. Aerodynamic conductance (ga) was well fitted to an exponential function of the wind stress; gC clearly decreased as the vapour pressure deficit (d) increased; gC related to air temperature through d. Although grass cover was sparse at the study site, the anticipated effect of soil moisture on E and gS was only slightly suggested and thus not deducible. On the 10‐day‐interval time scale, the effect of vegetation cover on evapotranspiration was insignificant compared to that of surface soil moisture. Changes in soil evaporation, related to precipitation, mainly caused the very large inter‐annual differences in evapotranspiration. The relationship between evapotranspiration and surface bulk resistance at the study site could therefore be fit to an exponential function. Copyright © 2007 John Wiley & Sons, Ltd.