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FY 1998 Second Quarter Milestone Report
GOAL: PREDICT AND ASSESS DECADAL-TO-CENTENNIAL CLIMATE CHANGE
OBJECTIVE: FURNISH PREDICTION, ASSESSMENT AND HUMAN-IMPACTS INFORMATION
PM: develop observational strategies, predictive models and understanding
for the effects of decadal-scale climate change in the Great Lakes.
Milestone: Evaluate the use of natural markers (i.e., time and the
temperature of maximum density) for detecting climatic trends in historical
water intake temperature data in the Great Lakes region.
Scientist: M. McCormick michael.mccormick@noaa.gov (GLERL; 734-741-2268)
In the Great Lakes region the observational evidence for climatic change has been primarily limited to changes in lake-ice conditions, for which there are consistent records going back prior to the turn-of-the-century. In general, consistent water temperature data sets that cover a time period sufficient to reveal long-term changes that might reflect climatic trends are difficult to find. However, long-term historical water temperature records have been collected and maintained at some of the many water intakes around the Great Lakes. The goal of this project was to evaluate the utility of such data sets for detecting climatic trends. Seven nearshore water intake sites in the Great Lakes (Bay City, MI; Green Bay, WI; Sault Ste. Marie, MI; St. Joseph, MI; Sandusky Bay, OH, Put-In-Bay, OH; and Erie, PA) were chosen and their data examined for climatic trends. A new approach facilitated determination of the interannual variability in the timing of the 4oC temperature of maximum density.
Analyses of these data revealed climatic trends in nearshore water temperatures for the first time. Two of the three sites with data records extending back to the early part of this century (Sault Ste. Marie and Put-In-Bay) showed an identical rate of increase in the maximum potential duration of summer stratification (DSS) of 4.8 hours per year. Over the period 1920 - 1990 this equates to a 14 day increase in the potential DSS. Over the period from 1960 - 1990 six of the seven sites studied (all but Green Bay) showed significant trends towards an increase in the potential DSS with a median rate of increase of 14.8 hours per year, resulting in a net change of nearly 18 days. The rate of increase in the duration data was skewed, with most of the increase due to an earlier transition to spring-like conditions. However, the data do not extend far enough back in time to know if these climatic trends are part on an unresolvable natural cycle or forced by anthropogenic activity.
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