The utility of thermal satellite images and land-based meteorology to estimate evaporation from large lakes

Abstract

Evaporation measurements over lakes are limited by physical constraints, logistics and financial demands. Thermal satellite images and land-based meteorology can be combined to derive evaporation rates from large lakes. The Dead Sea is a large hypersaline lake that can be used to examine the utility of thermal satellite images along with land-based meteorology to assess evaporation rates. Sea surface tmperature was retrieved for a 12-month period using band 10 onboard Landsat 8. Monthly SST was combined with nearby land-based meteorology to estimate evaporation from the sea surface using a mass transfer method and two variations of the Penman procedure. The Mass transfer gave an annual evaporation rate of 1005 mm whereas the Penman and the Priestley-Taylor methods gave 1308 and 1140 mm, respectively. These values are commensurate with extensive field measurement and theoretically derived evaporation values. Analysis shows a tradeoff between wind speed increase over the smoother lake surface and the drop in the saturation water vapor pressure deficit across the lake-atmosphere boundary. Wind speed has profound effects on evaporation differences during the warm season but diminish appreciably in the cold season when the vapor pressure deficit is small. Thermal images were able to resolve the presence of large pockets of cool water over the Dead Sea resulting from freshwater input. Modifications to evaporation caused by freshwater input to a hypersaline lake are investigated from a thermodynamic perspective. The alteration to evaporation depends on the simultaneous departure of surface temperature and the activity of the brine.