By STEVEN MAIER
Capital News Service
LANSING — Predicting water levels in the Great Lakes isn’t as straightforward as it would seem.
A warm winter has led to lower ice coverage — just 5 percent of the Great Lakes was covered with ice as of March 1. The average coverage at this time for the last 40 years has been 43 percent, according to the Great Lakes Environmental Research Laboratory in Ann Arbor.
Less ice means less protection from evaporation and, theoretically, lower water levels, said Jacob Bruxer, a senior water resources engineer with Environment and Climate Change Canada.
But it’s not quite that simple. And not the case now.
That’s because water levels are a function of many factors, Bruxer said.
“Everyone wants to make that into a big story — about how ice cover is affecting water in the lakes,” Bruxer said. “I would just stress that evaporation is very complicated.”
Last winter was also warm and with less ice than usual, he said. But that didn’t result in below-average water levels either.
Water levels in the Great Lakes are driven mostly by evaporation, precipitation and runoff, according to Drew Gronewold, a hydrologist at the Great Lakes Environmental Research Laboratory.
Of the three factors, precipitation has the most influence. And, Bruxer said, there’s no correlation between ice cover and precipitation.
Gronewold and his colleagues use water gauging stations around the Great Lakes for year-round monitoring, entering the data into an online display. Despite the scant ice cover, each lake is slightly higher than average.
But that’s not much of a story, according to Bruxer.
“The notion that they’re high is vague and maybe not very accurate,” Bruxer said.
Over the last three years, water levels have been higher in Lake Huron, Lake Michigan and Lake Superior than they had been in the last decade. But the past decade has been a period of low water for each.
Gronewold said shifts in water levels tend to make people uneasy but are actually natural. He said he thinks people tend to forget “that there is a range of variance in the Great Lakes water levels.”
He’s not referring just to seasonal changes. Water levels can shift dramatically over years.
People often get used to a certain level and forget to account for the possibility of changes, Gronewold said, and they may be alarmed about higher water because they’d become used to lower levels over the last 10 years.
Warm winters don’t appear to be wreaking havoc on water levels. The question then is whether the warming global climate will change that.
Current climate change models predict more precipitation in the region because warmer air is able to collect more moisture, Gronewold said. But warmer air also means more evaporation, and scientists aren’t sure which factor will win out.
The lakes follow a similar pattern each year, rising in the spring and falling in the autumn. And Bruxer said what lake levels will be like this summer depends on the amount of rain in the spring.
Steven Maier writes for Great Lakes Echo.
By STEVEN MAIER