Lake levels and climate change

November 25, 2008

By Jennifer Yauck

Last year, the 34-foot sailboat Falcon unwittingly became a local attraction after running aground near Bradford Beach, a victim of operator error and below-average water levels in Lake Michigan.

Among boaters at the South Shore Yacht Club who hope to avoid grounding their own craft or bumping lake bottom, lake levels are always a topic of discussion, according to club Vice Commodore Bruce Nason. The issue is particularly important during the club’s annual Queen’s Cup race, which hosts large sailboats with 10- to 12-foot keels, he said. “Everybody pays attention to what’s going on with lake levels.

Ship in Milwaukee's near shore waters
Ships must reduce their loads by about 270 tons per one-inch decline in lake levels. This translates into higher transportation costs, and in turn, higher prices for consumers. ~photo Jennifer Yauck

Scientists, too, are paying attention to Great Lakes levels, and investigating how climate change and climatic variability might influence lake levels over the next century. Several studies project levels will decline, impacting boating as well as shipping, dredging, and beaches.

Ups and Downs

Great Lakes water levels constantly fluctuate and are affected by both human and natural influences. Existing manmade diversions of water into and out of the lakes, for example, have raised some lake levels and lowered others by several inches, according to the Great Lakes Commission and U.S. Army Corps of Engineers.

Larger fluctuations occur naturally each year as the lakes rise and fall with the seasons. According to the U.S. Geological Survey (USGS), the difference between Lake Michigan’s summertime high and wintertime low each year averages about one foot.

Lake levels also fluctuate over longer timescales. Lake Michigan has had below-average levels for nearly a decade; levels were also especially low during the mid-1920s, mid-1930s, and mid-1960s. They were especially high during the early 1950s, early 1970s, and mid-1980s. The difference between the high and low of the past century is about six feet, according to the USGS. Scientists attribute some of these longer-term fluctuations to natural variations in climate thought to be driven in part by global phenomena, such as large-scale interactions between the oceans and atmosphere.

Lake Michigan Water Level History

Lake Michigan’s water level constantly fluctuates and is affected by both human and natural influences. The red line shows the lake’s long-term average level (feet above sea level) between 1918 and 2007. Source: U.S. Army Corps of Engineers data. ~courtesy Jennifer Yauck

But scientific evidence suggests human-induced climate change-driven by emissions of carbon dioxide and other heat-trapping “greenhouse” gases into the atmosphere-could also influence lake levels over the long term. A recent report on human-induced climate change commissioned by the Chicago Climate Task Force projects a one- to two-foot drop in Lake Michigan’s water level over the coming century if worldwide fossil fuel use continues unabated. It projects a zero to one-foot drop if fossil fuel use declines.

The projections are based on simulations from three climate models and a Great Lakes Basin water flow model. Some previous studies projected larger declines (and at least one projected an increase), but those studies used less sophisticated climate models.

According to Don Wuebbles, University of Illinois professor and atmospheric scientist and a lead author of the Chicago report, the analysis suggests Chicago will experience higher temperatures, more evaporation, more spring and winter precipitation, less summer precipitation, and more heavy-precipitation events over the next century. Milwaukee would see roughly similar conditions, he said. The net effect of these and other related changes would lead to Lake Michigan’s projected decline.

“Our future will likely be a combination of water level changes from greenhouse gases and from natural climatic variations at annual and decadal time periods,” said John Magnuson, a University of Wisconsin-Madison professor emeritus who helped assess aquatic impacts for the Intergovernmental Panel on Climate Change. Together, he said, the two influences are likely to lead every 15 to 25 years to lower lows than the lakes have experienced in their more recent history. “We’ll probably see fewer future impacts of high-water years and more future impacts of low-water years,” he said.

Adapting to Impacts

Potential low-water impacts are both economic and environmental. When lake levels decline, shoreline structures like piers need to be altered. Ships must reduce their loads-by about 270 tons per one-inch decline, according to the Lake Carriers’ Association-translating into higher transportation costs. More dredging is often required to keep waterways open, resulting in removal and disposal costs and the possible resuspension of polluted sediment. Lower levels can also decrease hydropower production and jeopardize water intakes used by water utilities and industries. More positively, lower levels can expand beaches and reduce coastal erosion.

Magnuson suggested human systems be designed to be “resilient enough to survive variations” in water levels in the future, and emphasized the importance of developing adaptive strategies in general to deal with climate change impacts. Some work on this has already begun through the Wisconsin Initiative on Climate Change Impacts. “We need to do the best we can to minimize the effects of changes that are well underway,” Magnuson said.

Jennifer Yauck is a science writer at the Great Lakes WATER Institute. GLWI (glwi.uwm.edu) is the largest academic freshwater research facility on the Great Lakes.

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