Developing Methodology to Characterize Soil Limited Evaporation.

Understanding soil water evaporation and associated energy exchange between land and atmosphere in the form of latent heat of evaporation (LE) is very important for hydrologic, environmental studies as well as for crop water management.   Large-scale hydrologic and climatic patterns have been traditionally misrepresented in the sense that various land surface models are based upon the assumption that evaporation occurs (or LE originates) at the soil surface. However, during the soil limited evaporation stage, the zone of evaporation extends below the soil surface. There is need to better understand soil driven evaporation and develop methodology to estimate depth and magnitude of subsurface evaporation in order to accurately quantify surface water and energy balances. Recent work indicates the potential for soil sensible heat balance to be used for measurement of evaporation in the field. To better understand the physics of soil controlled evaporation, it is necessary to test this methodology under controlled lab conditions as opposed to the complex field conditions. Laboratory column studies are being conducted with objectives (1) to test heat pulse method based on energy balance approach for in situ measurement of soil water evaporation by comparing it with mass balance and (2) to understand the physics of evaporation by studying the effect of depth to water table, soil characteristics and boundary layer conditions on depth and magnitude of subsurface soil water evaporation. Preliminary results and model analysis will be presented.