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Evaporation of Water From Soils As Influenced By Drying With Wind or Radiation¹

ABSTRACT

The evaporation rate from three soils initially wet was made the same by adjusting the wind and radiation intensity. The wind treatment caused a temperature depression at the soil surface initially which nearly disappeared after about 5 days. The radiation treatment caused a temperature increase at the soil surface which increased with time. Soil water content profiles measured as a function of time showed the water content near the soil surface to be higher for the wind treatment than for the radiation treatment. The components of flow due to temperature and suction gradients for both liquid and vapor flow were estimated using the analysis of Philip and de Vries. This analysis indicated the cumulative downward vapor flow due to temperature gradients amounted to about 10% of the net upward flow in 40 days at the 5-cm depth for one soil for the radiation treatment. Computations of evaporation assuming isothermal conditions for soils initially wet to near saturation would probably estimate total evaporation within 10%, and probably be sufficiently accurate for many purposes.

Key Words: vapor flow • liquid flow • temperature • soil water flow

¹ Contribution from the Northern Plains Branch, Soil and Water Conservation Research Division, US Department of Agriculture.

² Research Soil Scientists and Soil Scientist, respectively, US Department of Agriculture, Ft. Collins, Colo.

Received for publication February 2, 1967. Accepted for publication May 10, 1967.