Approximate analytical descriptions of evaporation from 1950-1980: how good were they?

During 1950-1980 theoretical descriptions of the soil hydrologic cycle were usually greatly simplified by either ignoring some physical processes deemed less important and/or approximating those considered necessary. Infiltration, drainage, and evaporation were often treated separately and even phases within each of these were isolated artificially and simplified. This was true despite the fact that much of the essential and complete physics of soil moisture (and associated heat) flow had been properly established in the 1930's. The limitation to using more complete theoretical descriptions of soil moisture and heat flow during 1950-1980 was the unavailability of easily accessed and inexpensive computer resources that would allow timely solution of the partial differential equations governing soil hydrology. Although there will always be a need for simple (but sophisticated) hydrological process models, computing power is now no longer limiting. During his graduate studies at Wisconsin Andy Black and co-authors, in widely known paper (SSSAJ 1969, 33: 655-660), used simplified flow theory to describe evaporation, drainage, and storage for a bare Plainfield sand located in a large-scale field lysimeter. For my PhD degree at UBC under Andy's supervision, I experimentally investigated soil heat and moisture regimes in a drying bare soil during spring at Agassiz, British Columbia. During that time, and since, I have become very familiar with the range of approximate and exact methods for describing evaporation (and the other processes) in the hydrologic cycle. It is now of interest (at least to me) to investigate the accuracy of the many of the approximate solutions in vogue earlier by comparing them with essentially exact numerical solutions of the heat and moisture flow equations. Some results of such an investigation are reported in this presentation and eventual published paper.