EFFECTS OF SOIL MOISTURE HETEROGENEITY ON SPATIALLY AVERAGED EVAPORATION

Abstract

Land surface is much more heterogeneous than atmosphere. To couple land surface hydrological processes with atmospheric dynamics, a model for estimation of spatially averaged hydrological responses over a large land area should be developed by adequate inclusion of the effects of land surface heterogeneity.
In this paper, the seasonal variations of soil moisture heterogeneity and spatially averaged evaporation were investigated by the field observation, process study and modeling in the Tibetan Plateau which has been considered to play an important role in the seasonal and internal variations of the Asian summer monsoon. Spatial distributions of soil moisture are characterized by considering the seasonal march of hydrological processes in the permafrost region. A land surface model which can express the pattern of soil moisture distribution is developed and validated by using the observed data. Two methods for estimation of spatially averaged evaporation are compared; one by using spatially averaged soil moisture and the other by considering the soil moisture heterogeneity. The results of the two methods are quite different during the trasnitionary phase from dry to wet while they are almost equal in the dry period and the wet one.