DIURNAL EVAPORATION FROM FRESH AND HYPERSALINE SHALLOW PONDS IN A HOT, DRY ENVIRONMENT

Abstract

A numerical procedure is developed to evaluate the diurnal trend of evaporation from a shallow freshwater pond and a hypersaline pond, both of which are 2 m deep and encountering identical meteorological forcings. Evaporation from both water bodies is calculated using Penman-Brutsaert formulation in which atmospheric buoyancy is calculated based on the semi-empirical theory of Monin-Obukhov formulation. A new iterative procedure is presented in this paper to solve for the water temperature. The present model attains a rapid convergence and compares favorably with temperature and evaporation observations obtained for a hypersaline pond and deep sunken pans. Calculations show that the average daily evaporation rates from the hypersaline pond during January and July are 0.5 and 6.4 mm day-1. Corresponding values for the freshwater pond are 2.4 and 10.45 mm day-1, respectively. Salinity suppresses evaporation strongly during winter because of its coupling effects on net radiation and saturation vapor pressure. During summer, energy availability accounts for 74% and 64% of total diurnal evaporation from the hypersaline pond and freshwater, respectively. In winter, however, the aerodynamic term accounts for about 80% of evaporation from both water bodies. Heat storage/release within the underlying sediments appears to be negligibly small and may be neglected with very little loss of accuracy when formulating the energy balance of shallow lakes. [Key words: evaporation, buoyancy, hypersaline solutions, Dead Sea, energy balance.]