SIMULATED CLIMATE-CHANGE EFFECTS ON ICE AND SNOW COVERS ON LAKES IN ATEMPERATE REGION

A simulation model for ice and snow covers is applied to dimictic and polymictic lakes of the temperature zone to project the effects of pos sible climate warming on ice and snow covers. The winter cover model i s associated with a deterministic, one-dimensional water temperature m odel. The lake parameters required as model input are surface area (A( S)), maximum depth (H-max), summer and Secchi depth as a measure of ra diation attenuation and trophic state. The model is driven by daily we ather data. The model has been validated with extensive data. Standard errors between simulated and measured values are 0.12 m for ice thick nesses, 0.07 m for snow covers and less than 6 days for ice formation dates. The model is applied to simulate effects of projected climate c hange on winter ice and snow covers on different types of lakes in Min nesota. Lake depth and latitude are shown to have the strongest influe nce on freeze-over dates. Lake morphometry causes variations of up to 6 days in the mean value of ice-in dates. The trophic state and shape of a lake have little effect on ice-out date, but latitude is importan t. The projected climate change due to a doubling of atmospheric carbo n dioxide (2 X CO2) is obtained from the output of the Canadian Climat e Center Global circulation Model (CCC GCM) and the Goddard Institute of Space Studies at Columbia University (GISS GCM). The 2 X CO2 climat e delays the ice formation by as much as 20 days, reduces maximum ice and snow thicknesses by 50%, and shortens the ice cover period by up t o 60 days. These changes would eliminate fish winterkill in most shall ow lakes, but would endanger snowmobiles and ice fishermen. To illustr ate the effect of projected climate change on winter ice/snow cover ch aracteristics, separate graphs are presented for values simulated with inputs of past climate conditions (1961-79) and with a projected 2 X CO2 climate scenario. Independent variables used on these plots are a lake geometry ratio A(S)(0.25)/H-max and Secchi depth. The lake geomet ry radio measures the susceptibility of a lake to stratification.