Boosted by above-average rainfall this spring, Lake Michigan is on pace to swell to its highest water level in two decades.

The rising water, which could climb more than 1 1/2 feet above its long-term average this month, has swallowed up mounds of beach along Illinois’ shoreline and created an opportunity for taller, stronger waves that could accelerate erosion. With forecasts suggesting Lake Michigan could remain high through the next six months, according to the Army Corps of Engineers, communities will likely be on guard for powerful autumn storms that could pulverize lakefront property.

The surge was brought on, in part, by an unexpected deluge this spring, when Chicago saw 43 percent more precipitation than usual, including an April with nearly double the normal rainfall, according to data from the National Weather Service.

“We always think of the Great Lakes as responding very slowly to these events, but they can actually be moving rather quickly,” said Illinois State Climatologist Jim Angel.

During 15 years of persistently low levels, Lake Michigan dipped to a record low in January 2013. In a dramatic reversal, two years later it rebounded nearly 4 feet, largely because of increased ice cover from back-to-back polar vortex winters that limited evaporation. Lake levels have continued to be elevated, though they are still 2 feet below the record high set in 1986.

Periods of high and low lake levels have drawbacks, said Keith Kompoltowicz, chief of watershed hydrology for the Army Corps of Engineers Detroit District.

“For a decade and a half, we had impacts from low lake levels, and those issues are mainly access-related,” Kompoltowicz said. “You can’t get your boat into the harbor. A commercial vessel carries less cargo because of insufficient depth. There’s much more shoreline exposed which may increase the amount of unsightly vegetation that grows.

“Flip the switch to high levels, and the issues shift to more of a property angle,” he said. Bigger waves increase erosion and flooding, and they carry the potential for structures to be damaged.

Water levels on all five Great Lakes — the world’s largest system of freshwater lakes — currently exceed their historical average.

Lakes Michigan, Huron, Superior and Erie are expected to reach their highest average monthly levels since the late 1990s, while Lake Ontario rose in May to its highest average mark since agencies began keeping records in 1918, the Army Corps announced this week.

As the water levels have risen, the shrinking beaches and bigger waves haven’t escaped the notice of local residents.

Ihor Hulovatyy, who moved to Chicago from Ukraine in 2012, said he goes for a swim every morning before work. Even in the winter, he takes a quick dip in the bracing water, or if the lake is iced over, simply stands in the snow. Hulovatyy, who lives in the Near North neighborhood, said because there was less ice this winter, he was able to spend more mornings in the water.

“The water isn’t as cold as before,” he said Wednesday, moments after getting out of the lake at Oak Street Beach. “But I feel that the waves are much stronger this year.”

Ron Guinazzo, who was walking up and down the beach with his metal detector looking for coins in the sand, agreed. The beaches are getting shorter, washed away by waves and sinking into the lake, he said.

The Great Lakes water levels generally peak in the summer after they are nourished by runoff from melting snow and rain in spring. So, forecasts initially predicted a slight decline in lake levels this summer compared with last year, because of mild winter temperatures and relatively little snowfall and ice cover.

However, experts found themselves surprised when “the faucet turned on” over the Great Lakes region in April and May, Kompolowicz said.

Chicago saw 13.7 inches of precipitation during the spring, more than 4 inches above normal, according to the National Weather Service. The downpours appear to be continuing with half an inch of rain recorded at O’Hare International Airport and 1 inch at Midway Airport on Wednesday.

Angel, the climatologist, said the sizable bump in Great lakes water levels is connected to an increase in heavy rainfall documented across the area. Springtime in Illinois has become about 15 percent wetter over the last century, a trend Angel attributes to climate change.

“The concept is that as you warm up the atmosphere, it is able to hold more water and the next thunderstorm can then take that moisture,” he said. “So there is a direct link between these heavy rainfalls and climate change.”

Experts also suspect lake evaporation was stunted over the winter. Usually, ice cover dictates how much evaporation can occur, but heavy cloud cover and warmer air temperatures likely contributed to less evaporation. Peak evaporation usually happens in late fall, when arctic air meets the relatively warm surface water. But last winter was not that cold, Kompolowicz said.

“It’s often a battle between how much water is coming in versus how much is leaving,” he said.

Forecasts by the U.S. Army Corps of Engineers indicate Lake Michigan levels will stay above their historic average heading into the fall, a season in which powerful storms have historically punished the Illinois shoreline.

During the 2014 Halloween storm, when lake levels were about a foot lower, winds whipped up 20-foot waves, which flooded Lake Shore Drive and tore away large slabs of asphalt along the Lakefront Trail on the Near North Side.

Pointing to the water lapping at the side of a concrete berm, Guinazzo said he recalled seeing 20-foot waves washing onto Lake Shore several years ago.

“If we get those storms now, the people on the other side of the road will be in trouble.”

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