WEATHER:

Heavy rains and snow pose Midwest flood threats but begin to replenish Great Lakes

Scientists monitoring water levels in the Great Lakes said yesterday that the massive freshwater basin must reach equilibrium among evaporation, precipitation and runoff for the lakes to rebound to optimum levels for recreation, commerce and fisheries.

But whether such equilibrium can be achieved, and for how long, remains an open question, said Drew Gronewold, a hydrologist at the National Oceanic and Atmospheric Administration's Great Lakes Environmental Research Laboratory in Ann Arbor, Mich.

The obstacle to making such predictions, Gronewold said, is the wide variation in model outputs showing how the Great Lakes will respond to climate change over the coming decades.

"The take-home message is that our uncertainty in future water levels, which is rather considerable, is a direct reflection about our uncertainty about the climate," Gronewold told reporters on an agency-sponsored webinar about Great Lakes water levels.

Several of the Great Lakes have experienced record-low water levels due to last year's high temperatures, regional drought and anemic snowpack. But this year could see water levels rebound, at least in the short term, due to the Upper Midwest's long, snowy winter and high runoff from recent rain events in the Lake Michigan-Huron basin.

As of this week, more than 150 river gauges on waterways in Ohio and Mississippi river basins are expected to reach or exceed flood stage, according to the Army Corps of Engineers, and numerous warnings have been issued about localized flooding in parts of Illinois, Wisconsin and Michigan -- where the Grand River rose nearly 4 feet above flood stage late Sunday at Grand Rapids, resulting in evacuations and a declared state of emergency.

Keith Kompoltowicz, watershed hydrology branch chief for the Army Corps' Detroit District office, which monitors the Great Lakes, said yesterday that above-average rainfall in the Lake Michigan-Huron basin has raised Lake Michigan's water level by 7 inches since April 1, and that swollen rivers draining into the basin should push the lake even higher over the next few weeks.

Farther north, in the Lake Superior basin, scientists note that a heavy snowpack that has accumulated into April should give a much-needed boost to the lake, which was among those recording record-low levels in January. This year's conditions contrast sharply to those of 2012, when the Lake Superior basin's snowpack was mostly gone by the end of March, Kompoltowicz said.

Gronewold of NOAA said that this year's low water levels in the Superior and Michigan-Huron basins broke records set in 1964-65. But the lakes have seen significant fluctuations over that nearly five-decade span, including near-record-high levels in the mid-1980s followed by significant lows in the late 1990s.

Complex interplay at work

He said Great Lakes water levels are determined by three natural processes: over-lake precipitation, over-lake evaporation, and inputs from streams and rivers that deliver water from upland areas. If any one of those three processes undergoes significant change, the lakes will rise or fall accordingly.

"Most of the changes you're seeing right now come about when there's a change in the interplay between precipitation and evaporation," Gronewold said. "They're the main drivers of the whole water budget."

Whether the current heavy precipitation and expected surge in water from this spring's snowmelt will help the lakes recover from last winter's record-low levels remains to be seen. While shippers and lakeshore communities could see a temporary reprieve from low water levels, experts note that the Great Lakes are very large water bodies, and it takes a long time for imbalances in the hydrologic system to right themselves.

"Certainly for those who want to see higher lake levels, a month of significant rainfall that causes the lake to rise by 7 inches is welcome news," Kompoltowicz said. But he cautioned against attaching too much significance to the recent high runoff, adding that the Superior and Michigan-Huron basins still remain several feet below their long-term average levels.

The Army Corps cautioned Great Lakes shippers early this month that vessels should expect lower water levels to persist for the first six months of the year, and some vessels may have to lighten their loads to pass shallower channels between the lakes.

Recreational boaters and lakefront property owners have also been affected by the low water levels, with docks that once protruded into navigable water now sitting atop mud flats.

"You can imagine if you own property on this lake and the shoreline was out beyond the end of your dock, that's not going to be a very good thing for you," Tom Landon, an engineer with NOAA's National Ocean Service, told reporters on yesterday's Web conference.

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