Potential Evaporation as a Manifestation of Regional Evaporation

The temperature and humidity of the lower atmosphere are treated as causes of evaporation from a small continuously moist area and as effects of evaporation from a large area with variable moisture supply. This leads to the formulation of a model in which the sum of the regional and potential evaporation is equal to the evaporation equivalent of the absorbed insolation. Such a formulation permits the regional evaporation, a product of climatic, soil moisture, and vegetation processes, to be estimated by its effects on climatologic or evaporimeter observations. Test data are derived from class A evaporation pan observations from the near‐arid regions of the southwestern United States, and the near‐humid regions of Ireland and from records of rainfall and runoff for Irish river catchments. Comparisons with the model predictions provide good evidence for the validity of the model and interesting insights into its hydrologic and climatologic implications.