Characterizing patterns of nearshore water temperature variation in the North American Great Lakes and assessing sensitivities to climate change

Nearshore waters are among the most biologically productive and anthropogenically developed in the North American Great Lakes. We examined site-to-site differences in the pattern of variation in the daily water temperatures observed at water intakes located in nearshore regions of the Great Lakes. Data from 28 nearshore sites spread across all five lakes were analyzed. At each site, daily differences between nearshore and lake-wide surface water temperatures varied systematically with season, and these seasonal patterns varied systematically from site to site. We characterized these patterns using an index derived from quantile regression. Index values were related to site-specific factors such as depth, fetch and exposure. We broadened these empirical analyses to develop a tool for extending, to nearshore water temperatures, previously published projections of climate change impacts on lake-wide mean surface water temperatures. This tool provided projections of the possible impacts of increasing surface water temperatures on nearshore water temperatures under a climate change scenario for the Great Lakes region. Projections were generated for nearshore sites characterized by a range of depth and fetch values representative of those found throughout the Great Lakes. Projected impacts varied with site characteristics, with likely implications for biological activity and human use.