EFFECT OF ALBEDO ON EVAPOTRANSPIRATION RATE

The problem was to evaluate the possibility of reducing the evapotranspiration of an irrigated field by increasing its reflectivity to incoming radiation. A numerical computation approach was used to solve the differential equations governing the transfer phenomena in a horizontally homogeneous atmospheric boundary layer and underlying soil. A few preliminary tests showed that although wind velocities were not accurately predicted, the effect of such inaccuracies on the energy budget results was not significant. Comparisons of calculated results for fields with natural albedo (0.25) and fields with albedo artificially increased to 0.40, indicated the following: 1. (1) Under a clear sky, the relative reduction in net radiation due to the treatment, was about 30%, as compared with only 20% reduction in the solar radiation absorbed at the surface. 2. (2) The major factors affecting the saving of water were the albedo and the wetness of the surface. Wind, surface roughness and thermal stratification were of only secondary importance. 3. (3) The savings in water due to the treatment were calculated to be roughly 30% for all wetness conditions. © 1969.