Dependence of bare soil albedo on soil moisture on the moraine of the Zongo glacier (Bolivia): Implications for land surface modeling

Abstract

Although the dependence of bare soil albedo on soil moisture is a familiar observation, it is not commonly represented in climate modeling. We investigate the impact of this dependence in a land surface model using meteorological data collected on the moraine of a Bolivian glacier. The relationship which is implemented to simulate albedo variations with soil moisture is deduced from a previous field study. The model is set up at the scale of the meteorological station plot to have the most accurate control on the model calibration and validation. A snow parameter is modified to account for the fact that the model was designed for larger cell sizes. Water content measurements are used to calibrate the parameter controlling the vertical water fluxes within the soil surface layer. This allows us to enhance the model's ability to capture the fast changes in surface soil moisture. The comparison of simulated ground heat flux and outgoing longwave radiations with observations shows that the model performs well despite the fact that all other parameters are set a priori on the basis of local properties of the surface. The results show that the dependence of bare soil albedo on soil moisture, which causes an increase in the net radiation, importantly influences the turbulent fluxes at the annual and monthly time scales. The mean annual evaporation is increased by 12%. As a consequence, this parameterization modifies the computed runoff, which is reduced by more than 5% during the rainy season. Copyright 2009 by the American Geophysical Union.