A Model and Experimental Study of Evaporation from Bare-Soil Surfaces

Abstract

A model is constructed for estimating evaporation from bare-soil surfaces. In the model, the evaporation is parameterized with the soil-water content for the upper 2 cm of the soil (Kondo et al.), and the heat and water transport within the soil layer below 2 cm is explicitly described by the heat conduction and moisture diffusion equations. Experiments on evaporation from loam packed in pans are also carried out. The present model well simulates the observed evaporation and vertical profiles of soil temperature and water content. Long time simulations of evaporation by the present model an compared with the force-restore method and the bucket model for a drying period of over several months. The decrease in evaporation rate for the bucket model is comparatively small. However, the evaporation by the present model and the force-restore method decreases rapidly several days after the beginning of the drying period. Differences between the evaporation by the present model and that by the force-restore method appear after approximately 10 days from the onset of the drying period. The sensitivity of the present model on the wind velocity is tested. The evaporation is sensitive to the wind velocity when the soil is wet, but less sensitive when the soil is dried because the soil resistance to the water transport becomes large as compared with the aerodynamical resistance.