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

A numerical procedure is developed to evaluate the diurnal trend of ev aporation from a shallow freshwater pond and a hypersaline pond, both of which are 2 m deep and encountering identical meteorological forcin gs. Evaporation from both water bodies is calculated using Penman-Brut saert formulation in which atmospheric buoyancy is calculated based on the semi-empirical theory of Monin-Obukhov formulation. A new iterati ve procedure is presented in this paper to solve for the water tempera ture. The present model attains a rapid convergence and compares favor ably with temperature and evaporation observations obtained for a hype rsaline pond and deep sunken pans. Calculations show that the average daily evaporation rates from the hypersaline pond during January and J uly are 0.5 and 6.4 mm day(-1). Corresponding values for the freshwate r pond are 2.4 and 10.45 mm day(-1), respectively. Salinity suppresses evaporation strongly during winter because of its coupling effect!; o n net radiation and saturation vapor pressure. During summer, energy a vailability accounts for 74%, and 64% of total diurnal evaporation fro m the hypersaline pond and freshwater, respectively. In winter, howeve r, the aerodynamic term accounts for about 80% of evaporation from bot h water bodies. Heat storage/release within the underlying sediments a ppeals to be negligibly small and may be neglected with very little lo ss of accuracy when formulating the energy balance of shallow lakes.