Parameterization of Evaporation from a Non-saturated Bare Surface for Application in Numerical Prediction Models

Abstract

Force restore treatment for the prediction of the surface volumetric soil water content proposed by Deardorff (1977) was applied to the precisely measured data of evaporation from the bare surface and soil water content close to the surface. Parameters C1, C2 and wb involved in the force restore method equation were investigated for the Kanto loam at Tsukuba, Japan.The results show that C1 monotonically decreases with an increase of the surface volumetric water content ws, and this relation is similar to that proposed by Deardorff (1978) for the Adelanto loam. The parameter C2 is not related to ws. It is suggested that C2 be taken as about 2 to 4 for the Kanto loam. It is shown that taking the soil water content at the depth of 1cm around 06JST as wb is effective for the further simplification of force restore treatment.Combination of the parameterization by the force restore method with the bulk method for the turbulent flux using the concept of surface moisture availability gives a good prediction of diurnal variations of evaporation and surface soil water content.

A determination of the Dalton and Stanton numbers over a saturated barley field

“…Assuming the solid ratio, defined as volume of solid phase divided by total volume of the soil, and the specific gravity (-weight of solid phase/volume of solid phase) as 0.25 and 2.65 which are typical values for loams in Japan, the volumetric soil water content, w, was estimated as 0.49-0.73 from w = 0.25 X 2.65M. With the analyses of Yasuda and Toya (1981) and Toya and Yasuda (1988) which show that the surface can be regarded as saturated when w is larger than 0.36, we considered that the barley field was sufficiently saturated. In this regard, we define the surface absolute humidity as the saturation absolute humidity for the surface temperature, i.e., a, = a*(T,).…”

ESTIMATION OF REGIONAL EVAPOTRANSPIRATION FROM ARID AND SEMI‐ARID SURFACES1

“…In arid and semi-arid regions, which occupy about one-third of the world's land surface, the land-atmosphere interaction, especially evapotranspiration, is very important with respect to global water balance and climatic change. In recent years, several studies have been completed on the estimation of ET from unsaturated surfaces (e.g., Barton, 1979;Yasuda and Toya, 1981;Toya and Yasuda, 1988;Lemeur and Zhang, 1989;Kondo et aL, 1989Kondo et aL, , 1991Flint and Childs, 1991;Stannard, 1993).…”