Some scientists are finding Lake Erie’s ice cover nearly as exciting as ice fishermen do. The ice’s effect on evaporation is more complex than previously thought.
With the record or near-record cold this winter, it’s not surprising that 93 percent of the surface of Lake Erie is frozen over.
But it’s not just ice fishermen who find that interesting. Scientists are learning that Great Lakes water levels are influenced more than previously thought by a complex interplay among evaporation, ice cover, fall and spring water temperatures, and atmospheric climate change.
A better understanding of how the lakes evaporate could, among other things, help improve public safety because meteorologists predict snowstorms and other forms of precipitation with more precision.
“I don’t think it would be a stretch to say some of these forecasts could be saving lives,” said John Lenters, senior scientist at LimnoTech, an environmental engineering firm in Ann Arbor. “If you improve evaporation forecasts, you improve weather forecasts.”
Mr. Lenters is the lead author of a new evaporation study undertaken by the Great Lakes Integrated Sciences and Assessments Center, a federally funded collaboration between the University of Michigan and Michigan State University that brought together a team of U.S. and Canadian scientists for one of the region’s broadest and most holistic investigations of Great Lakes ice.
Other authors included John Anderson, a Northern Michigan University geology professor; Peter Blanken, a University of Colorado geology associate professor; Christopher Spence, Environment Canada research scientist, and Andrew Suyker, a University of Nebraska-Lincoln associate professor.
Conventional thinking for decades has been that ice seals off or “caps” the Great Lakes from evaporation.
Unknown to many people, the lakes evaporate more in winter — before ice forms — than they do in summer because of the greater disparity between water and air temperatures.
That puts the water under stress and forces it to release energy in the form of evaporation.
Think of it like huffin’ and puffin’ through a workout.
The lakes are cooling off and adjusting to ambient conditions, almost like humans sweating, Mr. Lenters said.
“The lakes are essentially sweating in the fall and the winter,” he said.
The team’s research shows the lakes start evaporating a lot earlier in the fall than people might realize.
It also shows the rate of autumn evaporation plays a role in how fast the lakes cool and freeze.
“Thus, not only is the research showing that ice cover affects lake evaporation, but also the reverse — namely, that evaporation affects ice cover,” the report said.
Evaporation occurs not only when the lakes are stressed by temperatures. The low humidity of fall and winter helps accelerate evaporation, as do high wind speeds.
Some scientists shrug off the issue of evaporation. After all, it is invisible and extremely difficult to measure.
But the research team’s report claims evaporation is a huge, largely misunderstood concept.
On a typical day during fall and winter, the lakes could lose 0.4 to 0.6 inches of water to evaporation.
Not much, right?
Consider the total surface area of the Great Lakes is 94,250 square miles.
A one-day loss of 0.5 inches of water over that much area equates to a flow rate of 820 billion gallons a day, which the report said is “nearly 20 times the flow rate of Niagara Falls.”
The bottom line, according to Mr. Lenters, is that “things are much more complex than just a cap [of ice].”
“We aren’t necessarily refuting that effect. But what we’re finding is that — to really determine the net impact on evaporation and therefore, lake levels — you really have to look at what happened in the preceding year,” Mr. Lenters said.
To form a protective cap, several inches of thick, dense ice — at least a half-foot or more — need to form, Mr. Lenters said.
The benefit of ice extends beyond winter well into spring.
Heavy ice keeps water temperatures cool longer, curbing the evaporation rates for spring and early summer, Mr. Lenters said.
A constant process
Drew Gronewold, a hydrologist in the National Oceanic and Atmospheric Administration’s Great Lakes Environmental Research Laboratory in Ann Arbor, said the findings corroborate research of one of his most famous predecessors, retired NOAA hydrologist Frank Quinn, who has studied how Great Lakes water freezes, thaws, and circulates since the 1960s.
One of the biggest points to underscore is how evaporation is almost constant, whether or not ice forms, and that the springtime benefit of ice to keep water temperatures from rising too fast is almost as important as having the lakes freeze over, Mr. Gronewold said.
“It represents a very important contribution to the long-term understanding of this issue,” he said. “It represents an important stepping stone.”
One of Mr. Gronewold’s colleagues, George Leshkevich, a NOAA physical scientist in the same research lab, noted Lake Erie could lose water this winter, even though NOAA calculated that as of Saturday, 93.3 percent of the lake surface was frozen solid. It was the highest percentage among the Great Lakes, with Lake Superior at 85.3 percent; Lake Huron, 84.9 percent; Lake Michigan, 60.4 percent, and Lake Ontario, 32.1 percent. This is not unusual for the Ontario, as water moves through it quickly and it is believed to have frozen over only a few times in modern history.
As water vapor rises, it increases the chance of lake-effect snow. That pulls some of the water out of the lakes. Although most lake-effect snow stays in the Great Lakes basin, some is transported to other watersheds.
“Those lake-effect snows can be deposited outside the Great Lakes basin,” Mr. Leshkevich said.
The U.S.-Canada team based its findings on data generated by five research stations designed to monitor evaporation on a year-round basis.
Starting with an offshore lighthouse in the Stannard Rock area of Lake Superior in 2008, each was installed in open water. The process relies on sophisticated instruments to measure humidity and wind speed to calculate the exchange rate of water vapor to or from the lake surface.
The research team is calling for expanded monitoring.
“It’s still in kind of an infancy stage, trying to formalize this network,” Mr. Lenters said. “It’s still in the developmental stages.”
This winter has been a throwback, with its sustained deep freeze, heavy snow, and ice.
NOAA records show ice cover has been below average almost annually since 1998, right about the time lake levels plunged after about 30 years of being above average.
A joint report issued by NOAA and the U.S. Army Corps of Engineers in late November predicted that lake levels would move closer to their long-term averages in 2014.
Now that seems more likely than ever, Mr. Gronewold said.
“By next summer, water levels could approach their long-term average,” he said.
Data at UT
Closer to home, the University of Toledo’s Lake Erie Center has been collecting real-time data on the interchange of carbon dioxide, methane, and other greenhouse gases between western Lake Erie’s water surface and the atmosphere.
Jiquan Chen, a UT ecology professor who specializes in climate-change research, said he believes it’s one of the first projects of its kind. Few, if any, have focused on the nexus between the lake surface and the atmosphere.
The Great Lakes long have been overlooked as a potential source of greenhouse-gas emissions, with all of their decayed organic matter, as well as a potential sink to absorb and sequester gases.
It is not known if the lakes have a net effect in reducing or increasing greenhouse gases, he said.
“We have no knowledge of the role of lakes in climate change — if they are contributing to or affecting climate change, if they are sequestering more carbon than they are releasing,” he said. “That freshwater body may not be carbon-neutral.”
Understanding whether the Great Lakes have a positive or negative role in climate change could help advance evaporation research, Mr. Chen said.
UT’s Lake Erie Sensor Network has five sites with flux towers to measure greenhouse gases. They do this by tracking the exchange of carbon dioxide and water from the lake surface and atmosphere.
Two are on western Lake Erie. One is attached to the Coast Guard’s Toledo Light No. 2; the other is attached to the city of Toledo water-intake crib in western Lake Erie, three miles north of the city of Oregon’s shoreline.
UT also gathers data with a mobile flux tower attached to a boat.
“We do measure basic water chemistry and physics, but mostly the exchange between water surface and atmosphere,” Mr. Chen said.
Last month, the University of Wisconsin released a paper that states that variances in Great Lakes water levels generally have followed 10-year cycles — and that the fluctuations have been influenced by atmospheric trends as far away as the northern Pacific Ocean.
Water-level highs and lows may become harder to predict as the Earth’s climate continues to warm, according the study’s lead author, Carl Watras of the Wisconsin Department of Natural Resources, who also is a research fellow with UW’s Center for Limnology.
“The question looking ahead is, how they will behave as the climate evolves? Will we get more of both? Or will one begin to dominate?” Mr. Watras said.
Information from The Blade’s news services was used in this report.
Contact Tom Henry at: firstname.lastname@example.org or 419-724-6079.