Development of Ground and Remotely Based Evaporation Measurements at the Salar de Atacama, Northern Chile

Evaporation represents an important component of the water budget in desert playa lakes, and accurate spatial and temporal assessment of evaporation rates has the potential to greatly improve the accuracy of hydrologic models in such environments. To this end, evaporation at the Salar de Atacama, a large playa in the Atacama Desert of northern Chile, has been examined at a variety of spatial and temporal scales. Previous investigators have measured evaporation from the Salar using lysimeters and Bowen Ratio stations and have found that actual evaporation rates in much of the playa are extremely low (<10 mm yr^-1), in spite of shallow groundwater. Lake-scale evaporation can, however, be difficult to determine based solely on such point measurements, as evaporation rates may vary spatially as a function of water depth, crust type and vegetation. In this study, eddy correlation techniques have been used to validate and expand the database of evaporation rates on the playa surface. These evaporation rates in conjunction with measurements of meteorological parameters and other components of the land surface energy balance allow determination of evaporation rates using remotely sensed images. Thermal and visible near infrared bands from the Advanced Spaceborne Thermal Emission and Radiation radiometer (ASTER) on Terra I are being used to determine ground surface temperature, emissivity and albedo, values which are implemented into a numerical energy balance model to extrapolate evaporation rates over the entire playa surface. Preliminary results of evaporation and energy budget measurements taken during the first field campaign at the Salar are presented along with an assessment of the ability of ASTER imagery to provide accurate measurements of evaporation rates in playa environments.