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Influence of Different Diffusivity-Water Content Relations on Evaporation of Water from Soils¹

ABSTRACT

Estimates of the influence of variations in the diffusivity-water content relation on evaporation showed that where the diffusivity was changed at high water contents, evaporation was changed accordingly. However, variations in the D() relation at lower water contents showed little influence on cumulative evaporation.

Estimates were also made for layered soils with the D() relation for one layer 10 times that of the other layer. Cumulative evaporation increased significantly, if the diffusivity of the bottom layer was greater, as the depth of the surface layer decreased, provided the surface layer depth was less than half the total depth of the soil. Where the diffusivity was greater for the surface soil, cumulative evaporation increased as the depth of the surface layer increased.

All of the estimates were made based on the assumption that a diffusion-type equation is valid for evaporation.

¹ Contribution from the Northern Plains Branch, Soil and Water Conservation Research Division, ARS, USDA.

² Research Soil Scientists, USDA, Fort Collins, Colorado.

Received for publication February 10, 1965. Accepted for publication May 10, 1965.