|METRO DETROIT — Water levels on the Great Lakes have not only recovered over the past two years, but as of June, they are higher than they have been since the 1990s.|
All five Great Lakes and Lake St. Clair have passed their long-term averages as of October of last year — breaking more than a decade of low water levels — and they have continued to rise over time. The measurements come from the National Oceanic and Atmospheric Administration, the U.S. Army Corps of Engineers, and Environment Canada.
U.S. Army Corps of Engineers Chief of Watershed Hydrology Keith Kompoltowicz said the lakes along the southeastern side of Michigan — Lake Erie and Lake St. Clair — have both seen an 8-inch rise from May to June, in terms of the average lake level. Lake Michigan and Lake Huron, which are counted together, have gained more than that on the whole.
“If you look at the typical lake pattern (for those), the lake is usually leveling off instead of rising significantly this time of year,” Kompoltowicz said. “That’s a direct result of the extreme precipitation falling into the watershed of the southern Great Lakes in June.”
About 6.74 inches of water fell into the Lake Erie basin in June; normally, the lake receives an average of 3.47 inches of water. Kompoltowicz added that Lake Michigan and Lake Huron have seen the most dramatic increase in water levels since 2013: more than 4 feet. That is something that has happened on this scale only once in recorded history, back in the 1950s, he said.
Rainfall is not the only contributing factor to the lake levels. Andrew Gronewald, a hydrologist with the NOAA Great Lakes Environmental Research Lab, said that all the major drivers for lake levels have changed over the past few years.
In addition to over-lake precipitation, Gronewald said runoff entering the lake through tributaries and stormwater systems plays a factor, as does evaporation — where water in the lakes turns into a gas, lowering the overall water levels.
Evaporation primarily hits in the fall and winter, as temperature differences between the air and water — with colder air and warmer water — leads to evaporation and a drop in lake levels. Ice covers in the winter can reduce evaporation, as can colder water in the fall, Gronewald said.
“What we’re doing research on right now is trying to get a better understanding of what happened over the past two years that caused levels to rise so much,” Gronewald said. “It’s a combination of all the changes in all those drivers.”
In all, he said water levels are now the highest they have been since September 1998, though they should taper off the rest of the year. Typically, lake levels peak in June and hit their lowest point in January.
He said that at this point, there is no clear indication on what impact climate change is having long-term on the Great Lakes as a whole, due to all the variables involved.
“It’s unclear what the overall impact of climate change would be on all these different variables,” he said. “You have to look at them all at once. Increasing water temperatures could increase evaporation just as they did over the past 15 years, but it could also be that increased warming in general could increase precipitation, as well, and that’s something else we’ve seen.”
While the region has seen colder, snowier winters and more active storm systems in the past few years compared to the previous 15, Kompoltowicz said researchers do not know if this is going to be a long-term trend.
For the moment, though, Kompoltowicz said the rising water levels are beneficial for boaters wanting to get on the water, marinas trying to sell boat slips, and commercial shipping traffic, but for property owners along the shoreline, it can be more of a headache.
“Shoreline property owners are seeing smaller beaches, and there is more potential for erosion as strong storms affect the region,” he said. “I’ve talked to some folks that are watching their beach shrink from 20, 30, 40 yards of beach to 3-4 yards of beach because water levels have drastically risen over the past two years.”
Higher water levels can also lead to water being pushed inland more easily during storm events — leading to increased flooding — though Kompoltowicz said that since each storm is different, a specific area would be affected differently by each one.
Gronewald said erosion also depends on how the water and waves interact with the coastline and any structures along it.
He said researchers are starting the 30-year adjustment for measuring equipment to account for isostatic rebound, a phenomena in which land at northern latitudes gains elevation as glaciers recede. This causes gauges in the northern end of the Great Lakes system to indicate water level increases more quickly than the southern end.
Every 30 years, researchers need to take new measurements using benchmarks on the lakes that coincide, roughly, with the sea level. Gronewald said all current and historical measurements are then adjusted against that new measurement point so that scientists can observe long-term trends.