Albedo models for snow and ice on a freshwater lake

Snow and ice albedo measurements were taken over a freshwater lake in Minnesota for three months during the winter of 1996-1997 for use in a winter lake water quality model. The mean albedo of new snow was measured as 0.83 +/- 0.028, while the mean ice albedo was measured as 0.38 +/- 0.033. The period from December 17, 1996 to February 17, 1997, was marked as the nonmelt, or high albedo, season when albedo decayed at an average rate of 0.02 per day. The melting, or rapid albedo decay, season began on February 18 and continued until the end of the study on March 21. During the melt season the albedo decay rate varied from 0.10 to 0.20 per day. Two albedo models were developed for the entire winter season; they use separate equations for the nonmelt and melt periods. The input data for both models are climatic data. The first model requires daily incident solar radiation, air temperature, and snowfall data as input, while the second model requires daily air temperature and snowfall data only. The models predict albedo with modeling efficiencies of 0.94 and 0.89 for the entire three month period, respectively. The mean absolute error between values observed on the lake surface and values predicted by the model was 0.023 for the first model and 0.029 for the second model. Albedo predictions made by three albedo models given in the literature were also compared to the observed lake surface data. The two models developed herein predicted albedo better than the three existing surface albedo models because they were calibrated to the observed lake surface data. Albedo predictions from both new models and the three existing models were also compared to 11 years of observed surface albedo data collected over land. (No other lake surface observations were available.) The new models reasonably predicted albedo during those winters when the total snowfall depth was greater than 60 cm. The new model predictions for the land data were as good, if not better, than those by the three existing models. (C) 1999 Elsevier Science B.V. All lights reserved.