Concerning the Relationship between Evapotranspiration and Soil Moisture

Abstract

Evapotranspiration observations have traditionally been scaled by potential evapotranspiration as a means of unifying the soil moisture-evapotranspiration relationship under a variety of meteorological conditions. However, this scaling alone does not unify the relationship during the drying. supply-limited phase. In this paper, a second scaling parameter is identified which applies to this phase of evapotranspiration. The parameter is a maximum sustainable, or threshold evapotranspiration, which occurs in vegetation-covered surfaces just before leaf stomata close, and occurs when surface tension begins to significantly restrict the moisture release from bare soil pores. Simple expressions for this parameter are presented for the cases of vegetation cover and bare soil. The number of input variables required in these expressions is rather small. We examine the effect of natural soil heterogeneities on evapotranspiration as computed from the proposed model. It is shown that the observed natural var... Abstract Evapotranspiration observations have traditionally been scaled by potential evapotranspiration as a means of unifying the soil moisture-evapotranspiration relationship under a variety of meteorological conditions. However, this scaling alone does not unify the relationship during the drying. supply-limited phase. In this paper, a second scaling parameter is identified which applies to this phase of evapotranspiration. The parameter is a maximum sustainable, or threshold evapotranspiration, which occurs in vegetation-covered surfaces just before leaf stomata close, and occurs when surface tension begins to significantly restrict the moisture release from bare soil pores. Simple expressions for this parameter are presented for the cases of vegetation cover and bare soil. The number of input variables required in these expressions is rather small. We examine the effect of natural soil heterogeneities on evapotranspiration as computed from the proposed model. It is shown that the observed natural var...