POTENTIAL CLIMATE WARMING EFFECTS ON ICE COVERS OF SMALL LAKES IN THECONTIGUOUS US

To simulate effects of projected climate change on ice covers of small lakes in the northern contiguous U.S., a process-based simulation mod el is applied. This winter ice/snow cover model is associated with a d eterministic, one-dimensional year-round water temperature model. The lake parameters required as model input are surface area, maximum dept h, and Secchi depth as a measure of radiation attenuation. The model i s driven by daily weather data. Weather records from 209 stations in t he contiguous U.S. for the period 1961-1979 were used to represent pas t climate conditions. The projected climate changes due to a doubling of atmospheric CO2 were obtained from the output of the Canadian Clima te Center Global Circulation Model. To illustrate the effect of projec ted climate change we present herein winter ice cover characteristics simulated, respectively, with inputs of past climate conditions (1961- 1979), with inputs of a projected 2 X CO2 climate scenario as well as differences of those values. The dependence of ice cover characteristi cs on latitude and lake characteristics has been quantified by making simulations for 27 lake types at 209 locations across the contiguous U .S. It was found that the 2 X CO2 climate scenario is projected to del ay ice formation on lakes by as much as 40 days and melt ice by up to 67 days earlier. Maximum ice thicknesses are projected to be reduced b y up to 0.44 m (Sault Ste. Marie, MI), and the ice cover periods will be shorter by up to 89 days (Rock Springs, WY). The largest changes ar e projected to occur east of Idaho from the Canadian border down to th e states of Colorado, Nebraska, and Iowa and the northern parts of Ill inois, Indiana, Ohio, and Pennsylvania. These changes would reduce fis h winterkill in most shallow lakes of the northern states of the conti guous U.S. but may endanger snowmobiles and ice fishermen. (C) 1998 El sevier Science B.V. All rights reserved.