Rapid Water-level Rise Drives Unprecedented Coastal Erosion in the Laurentian Great Lakes, USA

Abstract:

Water level is a primary driver of change in coastal environments as it modulates the zone of influence for other physical drivers (e.g. waves). Along large lacustrine shorelines, such as those in the Great Lakes region, water levels can fluctuate over a meter on annual and decadal timescales. During high water-level phases, the zone of erosion shifts landward, resulting in obvious impacts to coastal habitat and infrastructure. From 2014 to 2020, Lake Michigan rose to record high water levels after over a decade of low water levels. These high water levels are only several centimeters above previous records set in the 1980s; however, the rate and magnitude of coastal erosion and habitat loss at some sites is an order of magnitude higher than previous high water periods. Our study evaluates the drivers of accelerated coastal habitat loss over the last decade along Lake Michigan and uses these process-response relationships to explore how climate change may affect large lake coastlines.

The 2012-2020 period had the greatest difference between minimum and maximum water levels and the greatest rate of rise for the 3 periods with the highest rates of habitat loss in the past century (2012-2020, 1974-1993, and 1961-1974). The rate of water-level rise during this period was double the rate for the other two periods. The high magnitude and rapid rate of rise observed during the 2012-2020 period in combination with a slight increase in the percentage of storm waves likely accelerated habitat loss rates beyond levels that have ever been observed over the past century. Our data suggest that rapid and dramatic changes from low water levels to high water levels are the main driver of large erosional losses, as the coastal system is shifted abruptly from one water-level regime to another. One likely impact of climate change on Great Lakes’ water level is an increase in the variability of fluctuations, thus more scenarios of abrupt and rapid water-level rise are expected in the future. This in turn will drive high rates of coastal erosion and associated habitat loss as was observed in this study. We propose that the unprecedented habitat loss observed during the 2012-2020 timeframe will become the new normal in the coming century as enhanced variability in water levels facilitate sustained coastal land loss.