Monitoring phenological changes in lake ice using the AVHRR: An integrative indicator of regional climate change
Variation in the periodicity of lake ice formation and breakup has often been suggested as an important climate change indicator (Scott 1964, McFadden 1965, Maslanik and Barry 1987, Robertson 1989, Magnuson 1990, Schindler et al. 1990, Wynne and Lillesand 1991). Lake ice periodicity can actually serve as a proxy for air temperature trends, which is quite important in light of the difficulties inherent in conventional temperature estimates (instrument intercalibration. urban heat islands) as well as the relative paucity of meteorological stations in the high latitudes, where most Global Circulation Models (GCMs) predict that global warming due to an increase in atmospheric carbon dioxide will be greatest (National Research Council 1982, Manabe and Wetherald 1986). In fact, Schindler et a!. ’s study examining the effects of global warming on lakes of Canada’s central boreal forest has already demonstrated a three-week increase in the ice- free season over the last 20 years. In this light we are exploring the use of data from the Advanced Very High Resolution Radiometer (AVHRR) to discriminate the presence and extent of lake ice on the 46 lakes and reservoirs in the state of Wisconsin with a surface area of greater than 1,000 hectares (Figures 1 and 3). This study has also necessitated further elucidation of the relationship between lake ice seasonality and lake morphometry for the lakes in the study area in order to more effectively isolate the influence of local climatic factors. This has involved multivariate regression of the dates of lake ice formation and breakup with the various lake morphometry indices and local meteorological data. For additional discussion on the basis for this research please refer to our report in the Technical Papers of the 1991 ACSM-ASPRS Annual Convention, entitled Satellite Remote Sensing of Limnologicallndicators of Global Change. Below is a summary of the methods being employed and the progress realized to date in our ongoing study; additional details will be presented in the course of our oral presentation.