Climate Change Impacts on Minnesota Lakes
Is climate change contributing to disappearing lake water?
By Stacy Nordstrom
When the water level of White Bear Lake in Minnesota dropped almost five feet from 2003 - 2013, researchers at the University of Minnesota’s Department of Soil, Water, and Climate wanted to understand what was happening.
The lake has historically had large water level fluctuation, partly because of its relatively small watershed, making it vulnerable to decreases in winter snowfall and spring runoff. Part of it could be land use change and the pumping of ground water. But what the researchers wanted to know was how much water was being lost through evaporation and if it is changing over time.
That’s where Land and Atmospheric Science graduate student Ke Xiao comes in. Together with his advisors, Dr. Timothy Griffis and Dr. John Baker and help from the Biometeorology lab group, Xiao set out to measure the evaporation of water from White Bear Lake and what it might mean for other lakes in the area.
From July of 2014 to February of 2017, the researchers set up two towers containing instruments out in the lake to measure fluctuations in wind velocity and water vapor (the eddy flux of water vapor) between the lake’s surface and the atmosphere.
The data revealed the lake lost approximately 22 inches of water through evaporation in 2014. In contrast, the lake lost around 30 inches in 2015 and 2016.
“More water was lost in 2015 and 2016 because the lake ice didn’t last as long for both of those season. That means the open water was exposed and vulnerable to evaporation for a longer period of time. The lake was also losing more water on an average day,” Xiao explained.
But what does that mean for the lake long term? And how is the evaporation changing over time? To answer those questions, Xiao and the researchers used the data to fine tune a climate model of the lake evaporation from 1979-2016. Their analysis showed that evaporation from White Bear Lake increased about 3.8 mm each year. But what about the future? Assuming a business-as-usual greenhouse gas emission scenario, they modeled the lake evaporation forward in time from 2017 to 2100. Annual evaporation is expected to increase by an additional 1.4 mm per year. This change is being driven largely by shortening the amount of time the lake is protected by ice cover.
The water level in White Bear Lake has been going back up due to an increase in precipitation in the last two years. The lower water level corresponds to regional drought, with little precipitation and large amounts of evaporation. However, the long-term modeling suggests the likelihood of lower water levels and more extreme fluctuations is expected to increase as our climate continues to change.
It’s not just White Bear Lake. This study implies changes in the regional climate impacts evaporation and lake levels all across the area. As Minnesota adjusts to this new reality, better water planning and management with consideration of climate scenarios are needed for the future of White Bear Lake and other Minnesota lakes.
Learn more about the research and see more of the results in the online, published paper.
Ke Xiao, Timothy J. Griffis, John M. Baker, Paul V. Bolstad, Matt D. Erickson, Xuhui Lee, Jeffrey D. Wood, Cheng Hu, John L. Nieber