National Geographic removed article about the Great Lakes
In 2012, National Geographic published this article about the dropping water level of the Great Lakes and blamed "climate change":
http://newswatch.nationalgeographic.com/2012/11/20/climate-change-and-variability-drive-low-water-levels-on-the-great-lakes/
As the lakes reached record levels in a few years later, they just removed this embarrassing article. Fortunately, I archived it:
Warming Lakes: Climate Change and Variability Drive Low Water Levels on the Great Lakes
Low water levels expose the sandy lake bottom on Lake Michigan. Photo by Jeff J. Cashman. For people living around the Great Lakes, water levels this past month have appeared much lower than many will remember. The upper Great Lakes reached near-record low water levels in October. This was most evident on Lakes Michigan...
November 20, 2012
Low water levels expose the sandy lake bottom on Lake Michigan. Photo by Jeff J. Cashman.
For people living around the Great Lakes, water levels this past month have appeared much lower than many will remember. The upper Great Lakes reached near-record low water levels in October. This was most evident on Lakes Michigan and Huron, where lake levels dropped to less than two inches (4 cm) above record lows and 28 inches (71 cm) below the long-term average. All five lakes, plus Lake St. Clair, remain below their long-term averages.
Rock and sand recently exposed by low water levels made stretches of the northern Lake Michigan shoreline look like a moonscape. Recreational boaters had trouble navigating the shallow water this fall, and shipping companies lightened loads to compensate for low water. Lakes Michigan and Huron hovered just above a record low set nearly 50 years ago, and Lake Superior was within five inches (11 cm) of a record low set in 1925.
A 2002 National Geographic magazine story, Down the Drain: The Incredible Shrinking Great Lakes, documents declining lake levels and the potential economic and ecological consequences for the region. Ten years later, the story continues to unfold, as water levels remain lower than normal.
Experts blame the recent low water on the unusually warm and dry weather over the past year. Rain events in October, including Hurricane Sandy, delayed the inevitable, but forecasters predict Lakes Superior, Michigan, and Huron will likely reach historic low levels in the late fall or winter, a time of year that the lakes are normally already dropping due to high rates of evaporation.
Water levels on Lake Michigan were within two inches of record lows in October and are expected to continue dropping as part of the normal seasonal decline through fall and winter. Photo by Jeff J. Cashman.
Low water levels are not the only climate-related trend being observed on the Great Lakes. Ice cover is also declining. The Great Lakes have lost 71% of their ice cover since 1973, according to a study by the Great Lakes Environmental Research Laboratory (GLERL). This past winter, the Great Lakes, including Lake Superior, were virtually ice free with just 5% ice coverage, the second lowest on record. Similar to the global assessment conducted in 2000, loss of ice cover is being reported on lakes throughout North America, Europe, and Asia.
Lake Superior is one of the most rapidly warming lakes in the world.
Summer lake temperatures are also on the rise. As mentioned in one of my previous posts about warming lakes, the Great Lakes are among many lakes in the northern hemisphere experiencing a rapid warming trend. Lake Superior, the largest freshwater lake in the world by surface area and third largest by volume (after Baikal in Siberia and Tanganyka in Africa), is also one of the most rapidly warming lakes in the world.
Because lower lake levels are considered one of the potential consequences of climate change, I was curious to find out whether there was any connection to what is being observed on the Great Lakes.
I recently had the opportunity to talk with John Lenters, a lake and climate scientist, while we attended a meeting of the Global Lake Ecological Observatory Network (GLEON) in Mulranny, Ireland. When comparing notes about our personal connections to Lake Superior, I learned that this accomplished scientist, with a laid-back, Midwestern manner, first fell in love with the Big Lake as a 14-year-old boy while on a backpacking trip in Isle Royale National Park. “Although the trip was grueling, I was awed by Lake Superior and realized I wanted to study lakes,” Lenters told me.
Now an associate professor at the University of Nebraska–Lincoln (UNL), Lenters studies lake-climate interactions in the Great Lakes region, the Alaskan Arctic, and western Nebraska. Given the global implications of his research, he joined GLEON in 2008 and helped to form the new Global Lake Temperature Collaboration (GLTC), hosting their first meeting at UNL this past June. With his boyhood dream as inspiration, he and his collaborators are leading the way to learning more about how climate change is affecting lakes around the world, including the Great Lakes.
Sunset on Granite Island, Lake Superior. Photo by John Lenters.
On Lake Superior, Lenters and his collaborators are studying the interactions among evaporation, ice cover, and water temperature. Their research builds on work by others in the region (and elsewhere) and provides new insight on factors affecting water levels.
Surface Water Temperatures Increasing on the Great Lakes
Similar to Lenters’ findings in a 2004 paper, which found Lake Superior to be warming more rapidly than summer air temperatures, Jay Austin (a GLTC collaborator) led a study of lake temperature trends at the University of Minnesota-Duluth’s Large Lakes Observatory (LLO). Published in Geophysical Research Letters, the LLO study found that summer surface water temperatures on Lake Superior have increased approximately 4.5°F (2.5°C) during the period 1979–2006.
The LLO study found that the decline in winter ice cover leads to an earlier start of the summer stratified season, a natural process in lakes when water near the surface warms, while deeper waters remain a more constant, cooler temperature. The earlier the lake becomes stratified in summer, the longer the warming period. “This results from a progressively earlier start of the summer stratified season, in response to a significant decline in average winter ice cover,” the study states. “Given a longer summer stratified season, surface waters can be heated to higher temperatures than that expected from increases in air temperature alone.”
Researchers also found a clear relationship between ice cover and summer water temperatures, which tend to be cooler following a winter with extensive ice cover. In contrast, winters with less ice cover tend to be followed by a summer with warm surface water temperatures. This is exactly what happened this year on Lakes Superior, Michigan, and Huron. The lakes were relatively ice free in 2011–12 and reached record-high water temperatures in the summer.
New Insight About the Interaction Between Ice Cover and Evaporation
Measuring evaporation rates on lakes as large as Superior is a very difficult and intensive process, so until recently, researchers in the Great Lakes region relied on models instead. The models correctly account for the various factors that impact evaporation rates, including when the lake surface is covered by ice. But with ice cover shrinking on all of the Great Lakes, scientists began to wonder what impact this would have on observed evaporation rates. Understanding this new dynamic required the installation of new monitoring stations on all five of the Great Lakes. Results are being shared through a network of researchers monitoring evaporation rates.
Lenters and his collaborators established a monitoring station on Granite Island in Lake Superior to measure evaporation rates. Photo by John Lenters.
In the past, experts assumed that as ice cover decreased, evaporation would increase, since more of the lake’s surface is exposed to the air during winter months. But a new paradigm is emerging.
“Some of our recent work challenges the standard paradigm that more ice cover means less evaporation,” Lenters told me. Evaporation rates are increasing as the climate changes, but the relationship to water temperature and ice cover is not as simple as previously thought.
Katherine Van Cleave, Lenters’ former student at UNL, recently completed a study of these interactions for her master’s thesis. Her study includes an analysis of the first direct observations of nearshore evaporation rates on the Great Lakes, using a high-tech monitoring station on Granite Island, near Marquette, Michigan. She also looked at some of the primary climatic factors driving this variability. Although her study period, from October 2010 to April 2012, does not include this past summer, the impact of the warm 2012 water temperatures on evaporation rates is entirely consistent with her findings.
Scientists use high-tech equipment to monitor evaporation from Lake Superior year-round. Photo by John Lenters.
Research by Lenters at Granite Island and a study with other collaborators at Stanard Rock (published in the Journal of Great Lakes Research) has examined seasonal and annual evaporation rates on Lake Superior. Together with research by Van Cleave, they found that evaporation rates in late winter and early spring (when ice cover is typically at a maximum) are generally minimal, even in years with low or no ice cover. The highest rates of evaporation, on the other hand, occur during the fall and early winter and, during particularly cold years, can actually lead to greater ice cover later in the winter and spring. “Evaporation is a cooling process,” explained Lenters, “and the more rapidly it occurs, the more likely the lake is to reach freezing temperatures and form extensive ice cover.”
Evaporation from a lake is similar to how we humans perspire to cool our bodies on a hot summer day. It is a process that transfers heat from the lake back into the atmosphere. When a lake evaporates, heat is released to the atmosphere. The more the lake “sweats,” the more it cools.
So instead of simply thinking of ice cover as a “cap” on evaporation, we need to realize that the reverse is also true – that strong evaporation can lead to high ice cover. In other words, says Van Cleave, “this ‘standard paradigm’ of decreasing ice cover, increasing water temperatures, and increasing evaporation may not stand as a full explanation of the role of evaporation in these processes. More evaporation in the fall will cool the lake quicker, leading to an earlier onset of ice cover.”
The Great Lakes, including Lake Superior, were nearly ice free during the winter of 2011-12. Source: NASA MODIS satellite photo from NOAA Great Lakes Coastwatch website.
But the lack of ice cover affects evaporation in another important way – by impacting water temperatures and evaporation rates much later in the year. “Ice cover was found to be a strong determinant of summer water temperature, and this in turn, can lead to changes in late-summer evaporation rates,” Van Cleave concluded.
Regime Shifts in the Great Lakes Ecosystem
Van Cleave found a regime shift in the Great Lakes ecosystem after extreme climate conditions in 1997-98. Photo by John Lenters.
Van Cleave made an interesting discovery after looking at long-term data for Lake Superior: Certain changes have not been linear through time. Scientists use statistical analysis to see if patterns emerge in their data and to determine whether certain parameters are increasing or decreasing with time. “Lake Superior experienced a pronounced change during the winter of 1997–98 when ice cover reached, at the time, record low levels,” her report states. “This was followed by record-warm summer water temperatures and near-record evaporation rates (surpassed only by 1987).”
“A step-change occurred in 1997–98 that resulted in a drop of ice duration of nearly 40 days, a 5.4°F (3°C) increase in summer water temperature, and a near doubling of July-August evaporation rates,” Van Cleave concluded. Ecologists refer to an abrupt change such as this as a regime shift, and although some evidence indicates that the lake recovered somewhat, Van Cleave found that these more recent trends ”are not statistically significant, suggesting that the 1998 regime shift has largely been sustained.”
Given the extreme conditions of this past year, Lenters wonders whether Lakes Superior, Michigan, and Huron are in the midst of another such regime shift.
Lake Levels Remain Below the Long-term Average
The U.S. Army Corps of Engineers (Corps) began keeping coordinated water level records in 1918. They base “record events” on calculations of monthly average lake level. Lake Michigan-Huron, considered one lake for hydrological studies because of the connection at the Straits of Mackinac, was 576.6 feet (175.74 meters) above sea level in October. The all-time record low for all months occurred in March 1964, when the lake dropped to 576.0 feet (175.58 meters).
The Great Lakes Water Level Dashboard, a handy, interactive online tool provided by NOAA, helped me to better visualize historic water level trends going back to 1861. I was reminded of a period of high water on the upper lakes during the 1970s and 1980s, when everyone was concerned about erosion along the lakeshore and houses were falling into Lake Michigan. What also jumped out are the below-average water levels after the 1997–98 event that Van Cleave described.
Screenshot of NOAA’s Great Lakes Water Level Dashboard showing Lakes Superior (top) and Michigan-Huron for the period 1918-2012.
Great Lakes water levels normally fluctuate throughout the year and from one year to the next depending on climate conditions. The lakes naturally cycle between periods of high water and low water, but abrupt changes in annual water levels are not unusual. These fluctuations are due to climate variability and are considered vital to a healthy ecosystem.
One variable the Corps constantly monitors is the supply of water to each Great Lake, which is made up of rainfall on the lake surface, runoff to the lake, and evaporation from the lake. In a teleconference with the media, Keith Kompoltowicz, chief of the Watershed Hydrology Branch in the Corps’s Detroit District Office, explained that this supply is the primary driver of water level fluctuations and that this past year, evaporation was much greater than precipitation and runoff combined. “Any time there is a scenario like that, lake levels will likely decline,” he said.
Lake levels are expected to continue dropping as part of the normal seasonal decline through the fall and winter. “Evaporation usually wins out at this time of year,” said Kompoltowicz.
Near-record low water levels on Lakes Michigan and Huron in October hovered just above a record low set nearly 50 years ago. Photo by Jeff J. Cashman.
Lakes Superior, Michigan, and Huron have been fluctuating below average levels since the extreme event 15 years ago. Corps officials acknowledged that the upper lakes have not recovered from this extreme event and are not likely to anytime soon. “We would need several months and seasons in a row of very wet weather to get us back to long-term average,” said Kompoltowicz.
This extended period of low water raises questions about whether climate change is contributing to declining lake levels, but the Corps maintains the position that it’s difficult to know, because the lakes continue to fluctuate within their normal range.
Low Lake Levels Renew Debate About Potential Causes
Controversy usually arises about potential causes whenever lake levels are low. Numerous theories abound. People ask whether a diversion in Chicago to the Mississippi River watershed might be to blame. Others point to erosion or dredging in the St. Clair River. John Allis, Chief of the Corps’s Great Lakes Hydrology and Hydrography Office, dismissed these claims, citing studies that show the Chicago diversion is more than offset by a diversion into Lake Superior from Canada.
Allis referred to a study of historic dredging and sand removal operations on the St. Clair River. “Studies show that the net impact of historic dredging and erosion is about 10 to 15 inches lower water levels in Lakes Michigan and Huron,” he said. “The last dredging project was completed in the 1960s, and since 1967, the only dredging that has been done on the St. Clair River is maintenance dredging to keep the rivers at authorized depths.”
The St. Clair River flows from Lake Huron to Lake St. Clair and the Detroit River. Historic dredging and sand removal projects resulted in water levels that are 10 to 15 inches lower on Lakes Michigan and Huron. Photo by Lisa Borre.
The Corps says that when water levels are low, they get asked about whether structures could be built to restrict flow in the St. Clair River. “Recent studies show that any of those projects could range from $50–200 million to construct,” said Allis. “Although water is low right now, there are many groups that would not support the construction of structures because of concerns about what would happen in high water.” He explained that projects to mitigate historic water losses were de-authorized in the late 1970s when the lakes approached record high levels.
The International Joint Commission (IJC) studied the impacts of dredging and erosion in the St. Clair River on water levels in the upper Great Lakes. Among other things, the International Upper Great Lakes Study (IUGLS) evaluated remedial measures for historic dredging projects and erosion. “The Study Board found that there had been some erosion in the St. Clair River between 1962 and 2000, but the riverbed had stabilized since then, making it unclear whether action would be appropriate,” said IJC Public Information Officer John Nevin. Further details can be found in the summary report.
Ships on the Great Lakes have lightened loads this fall due to low water levels. Photo by Lisa Borre.
The five-year, $14.6 million study by the Study Board also examined options for regulating water levels and flows in the upper Great Lakes system, consistent with the Boundary Waters Treaty of 1909. In March, the Study Board released its final report and recommended a new regulation plan for Lake Superior outflows, one that is “more robust than the existing plan and provides benefits, especially to the environment,” said Nevin. The new plan will not change regulation in a way that helps the situation on Lakes Michigan and Huron. “If we were to try to do that, it would damage Lake Superior,” he said. “It really can’t be done.”
A new regulation plan for Lake Superior will make it easier for ships transiting the Soo Locks and improve spawning habitat for endangered lake sturgeon in low water conditions. Photo by Lisa Borre.
The focus on past diversions and dredging operations is not surprising, given the complex nature of more subtle but very real changes underway. I asked Lenters for his opinion on other theories that explain why the lakes are so low this year. “No one bottled it up and took it away or diverted it to the Mississippi,” he said. “Together with the low precipitation we’ve seen this year, the lake water simply evaporated more quickly.”
Management Agencies Study Effects of Climate Change
With nearly 20% of the world’s surface freshwater at play and millions invested in restoration efforts, the stakes are incredibly high for understanding how natural climate variability and human-induced climate change affect the Great Lakes.
The IUGLS evaluated the impacts of climate change on lake levels in the Great Lakes region with state-of-the-art climate research. Projections suggest that “lake levels are likely to continue to fluctuate, but still remain within a relatively narrow historical range – while lower levels are likely, the possibility of higher levels cannot be dismissed.” Nevin explained it another way. “Low lake levels are not a new normal,” he said. “We expect to see lake levels fluctuate as we have in the past.”
State-of-the-art climate research conducted as part of the International Upper Great Lakes Study indicates that increased evaporation due to climate change will be largely offset by increases in local precipitation in the Lake Michigan-Huron basin. Photo by Lisa Borre.
The IUGLS acknowledges that despite uncertainties in the models used, “it is clear that evaporation is increasing and likely will increase for the foreseeable future.” The study further states, “Analysis indicates that in the Lake Michigan-Huron basin this increased evaporation is being largely offset by increases in local precipitation.” The outlook for Lake Superior is more cautious:
“In the Lake Superior basin, however, increasing evaporation over the past 60 years has not been compensated for by increased precipitation. As a result, the water supply has been declining in general in the basin. This trend is consistent with the current understanding of climate change. Unless changes in the precipitation regime occur, which is possible, [net basin supply] in Lake Superior will continue to decline, on average, despite the possibility of higher supplies at times.”
Experts predict that Lake Superior water levels will continue to decline, on average, due to increased evaporation rates caused by climate change. Photo by John Lenters.
These findings convinced the Study Board to recommend that “further climate analysis be undertaken to explore these dynamics” in order to provide more certainty in water supply estimates. Will changes in precipitation offset increased evaporation rates? Can lake levels recover from extreme events or are we seeing a new normal? These are some of the questions yet to be answered.
The IUGLS acknowledges that the Great Lakes basin is a complex system whose dynamics are only partially understood. In addition to further research, the Study Board recommends a more adaptive approach to future management – one that places climate change considerations in the mix. As the experience on Lake Tahoe shows, an important first step was acknowledging that climate change is a major driver in the ecosystem. Lake managers there are now focused on restoration projects that build the lake’s resilience to changes that are already underway.
Changes in ice cover, water temperature and evaporation indicate major shifts are underway on Lake Superior, the world’s largest lake. Photo by John Lenters.
Lenters explained that this past year was like a “perfect storm” of conditions leading to high rates of evaporation and low water levels on Lake Superior. “Record low ice cover in 2011–12, an extreme heat wave in March, and a warm, dry summer led to record-high summer lake temperatures,” he said. “As a result, we saw higher-than-normal evaporation rates earlier in the season.”
Lake Superior evaporation – which is typically very low during spring and early summer – doesn’t normally begin increasing until early August. But this year it began as early as late June. Together with the summer’s below-normal rainfall, lake levels began their annual decline in the summer rather than in the fall. This would explain the near-record low lake levels in October. “Lake Superior’s rapid warming is like a canary in the coal mine,” Lenters told me. “We’re seeing changes in ice cover, water temperature, and evaporation that indicate major shifts are underway on the world’s largest lake.”
Lisa Borre is a lake conservationist, freelance writer and sailor based in Annapolis, MD. With her husband, she co-founded LakeNet, a world lakes network that was active from 1998 to 2008, and co-wrote a sailing guide called “The Black Sea.” She is a native of the Great Lakes region and served as coordinator of the Lake Champlain Basin Program from 1990 to 1997.
About National Geographic Society
The National Geographic Society is a global nonprofit organization that uses the power of science, exploration, education and storytelling to illuminate and protect the wonder of our world. Since 1888, National Geographic has pushed the boundaries of exploration, investing in bold people and transformative ideas, providing more than 14,000 grants for work across all seven continents, reaching 3 million students each year through education offerings, and engaging audiences around the globe through signature experiences, stories and content. To learn more, visit www.nationalgeographic.org or follow us on Instagram, Twitter and Facebook.
Meet the Author
Lisa Borre
Lisa Borre is a lake conservationist, writer and avid sailor. A native of the Great Lakes region, she served as coordinator of the Lake Champlain Basin Program in the 1990s and co-founded LakeNet, a world lakes network that was active from 1998-2008. She is now a Senior Research Specialist at the Cary Institute of Ecosystem Studies and an active member of the Global Lake Ecological Observatory Network (GLEON). She is also on the board of directors of the North American Lake Management Society (NALMS), the advisory council of the Lake Champlain Committee, and an associate investigator with the SAFER Project: Sensing the Americas' Freshwater Ecosystem Risk from Climate Change. She writes about global lake topics for this blog and speaks to local, regional and international groups about the impacts of climate change on lakes and the need to work together to sustainably manage lakes and their watersheds. With her husband, she co-wrote The Black Sea, a sailing guide based on their voyage there in 2010.
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To the unending bad luck for the "man-made climate change" crowd, this period of low water levels in the Great Lakes was followed by a period of record high water levels, proving that everything they had written about "climate change" and the lakes was wrong.
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Several Great Lakes may reach highest water levels ever experienced in modern records
Updated Apr 03, 2020; Posted Apr 03, 2020
Fishtown in Leland, MI on April 2, 2020 showing record high water level on Lake Michigan. (Photo courtesy John Robert Williams)
By Mark Torregrossa | [email protected]
The six-month water level forecasts show a high-end forecast that could surpass all other modern water levels for some of the Great Lakes.
For the last three months, Lake Michigan and Lake Huron (which shares the same lake water level because they are linked) have set monthly record water levels. The monthly record water levels are expected to continue into summer. If we get significantly higher than usual precipitation, the water levels could slosh over the highest level ever recorded since good water level measurements began back in 1918.
Not much beach is left near Clinch Park Marina at Traverse City. (photo courtesy John Robert Williams)
Below is the forecast for Lake Michigan-Huron.
Lake Michigan and Lake Huron past water levels on left and next six months on right.
The green-dashed line is the most likely water level for Lake Michigan and Lake Huron this summer. Even the green-dashed line sets new record water levels. But the upper end of the red-striped area shows the range of possible outcomes. The upper end of the possible outcomes would take Lake Michigan and Lake Huron 5 inches higher than October 1986, the highest water level recorded since records began in 1918. July or August of this coming summer would be the months that could happen.
That would be a devastating high-water level for cities and beaches along the Lake Michigan and Lake Huron shoreline.
RELATED: Michigan’s shoreline towns struggle to survive Great Lakes High water
Remember one inch of water on Lake Michigan and Lake Huron is 800 billion gallons of water. If this summer’s water level reaches that upper end, Lake Michigan and Lake Huron would have 4 trillion gallons more water than the highest water level recorded by in the fall of 1986.
Lake Superior's water level in the past on left and forecast on the right.
Lake Superior will most likely stay below record water levels this summer. However, if Lake Superior gets into heavier than average precipitation, it could rise above all-time water levels also.
Lake Erie’s water level forecast below also shows the chance of highest water levels ever recorded in modern times.
RELATED: Interactive graphic shows historic water fluctuations on the Great Lakes
Water level forecast for Lake Erie shows the upper end of possibilities in the red striped wedge on the right.
Lake Erie’s water level forecast also shows a fairly high chance of water surging past previous water level records.
Lake Ontario water level forecast.
Lake Ontario also has a top-end forecast that brings the water level 4 inches higher than any water level ever recorded. If Lake Ontario does reach this devastating water level, it would be in June.
Traverse City Open Space shows water almost higher than the break wall. (Photo courtesy John Robert Williams)
The next few months of precipitation will dictate whether the Great Lakes flirt with old records or shatter old records. If old water level records are shattered, there won’t be much beach at many popular beaches around the Great Lakes.
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The follow-up claim was that "man-made climate change caused great variability in the level of the Great Lakes:
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https://www.scientificamerican.com/article/climate-change-sends-great-lakes-water-levels-seesawing/
Climate Change Sends Great Lakes Water Levels Seesawing
Six years ago, lake levels were low, now lakeside communities face widespread flooding
By Drew Gronewold, Richard B. Rood, The Conversation US on June 8, 2019
Caution sign at Queens Quay Terminal as the high water levels in Lake Ontario leave portions of Toronto's waterfront flooded, on May 31, 2019. Credit: Steve Russell Getty Images
The following essay is reprinted with permission from , an online publication covering the latest research.
The North American Great Lakes contain about one-fifth of the world’s surface fresh water. In May, new high water level records were set on Lakes Erie and Superior, and there has been widespread flooding across Lake Ontario for the second time in three years. These events coincide with persistent precipitation and severe flooding across much of central North America.
As recently as 2013, water levels on most of the Great Lakes were very low. At that time some experts proposed that climate change, along with other human actions such as channel dredging and water diversions, would cause water levels to continue to decline. This scenario spurred serious concern. Over 30 million people live within the Great Lakes basin, and many depend directly on the lakes for drinking water, industrial use, commercial shipping and recreation.
But since 2014 the issue has been too much water, not too little. High water poses just as many challenges for the region, including shoreline erosion, property damage, displacement of families and delays in planting spring crops. New York Gov. Andrew Cuomo recently declared a state of emergency in response to the flooding around Lake Ontario while calling for better planning decisions in light of climate change.
As researchers specializing in hydrology and climate science, we believe rapid transitions between extreme high and low water levels in the Great Lakes represent the “new normal.” Our view is based on interactions between global climate variability and the components of the regional hydrological cycle. Increasing precipitation, the threat of recurring periods of high evaporation, and a combination of both routine and unusual climate events—such as extreme cold air outbursts—are putting the region in uncharted territory.
Calculating the lakes’ water budget
Current water levels on the Great Lakes are setting records. Lake Superior, the largest freshwater lake on Earth by surface area, surpassed its record of 602.82 feet for the month of May, and is poised to set a new record for the month of June. Lake Erie, the world’s ninth largest lake by surface area, surpassed not only its record water level for the month of May, but also its all-time monthly water level record of 574.28 feet, which has stood since June 1986.
These extremes result from changes in the Great Lakes’ water budget—the movement of water into and out of the lakes. Water levels across the lakes fluctuate over time, influenced mainly by three factors: rain and snowfall over the lakes, evaporation over the lakes, and runoff that enters each lake from the surrounding land through tributaries and rivers. Runoff is directly affected by precipitation over land, snow cover and soil moisture.
Runoff from melting snow that accumulates around the Great Lakes each winter, shown here on March 25, 2019, is one element of the lakes’ water budget. Credit: NASA Earth Observatory
Interactions between these factors drive changes in the amount of water stored in each of the Great Lakes. For example, in the late 1990s surface water temperatures on Lakes Superior and Michigan-Huron rose by roughly 2 degrees C. Water evaporates more rapidly when it is warmer, and during this period evaporation rates were nearly 30% above annual average levels. Water levels on Lake Michigan-Huron dropped to the lowest levels ever recorded.
Then in 2014 the Midwest experienced an extraordinary cold air outbreak, widely dubbed the “polar vortex.” The lakes froze and evaporation rates dropped. As a result, water levels surged.
At roughly the same time, precipitation was increasing. The 2017 Lake Ontario flood followed a spring of extreme overland precipitation in the Lake Ontario and Saint Lawrence River basins. The 2019 flood follows the wettest U.S. winter in history.
What do these trends mean for water levels? In addition to the current onset of record highs, water levels in Lake Erie have been rising earlier in spring and declining earlier in fall. More winter precipitation is falling, often as snow. The snow is melting earlier in response to rising temperatures and shorter winters. The resulting runoff is then amplified in years like 2019 with large springtime rains. The net effect of this combination of hydrological events is that Lake Erie’s current water levels are much higher than usual for this time of year.
Significant lakeshore flooding and erosion along western #LakeErie this evening. Highest levels will occur this evening. This is uncharted territory with near record high levels. Help @NWSCLE by sharing your pictures and reports of flooding! #OHwx #CLEwx #Toledo #NWS #GreatLakes pic.twitter.com/qH7Wx1cANZ
— NWS Cleveland (@NWSCLE) May 8, 2019
The role of climate change
Great Lakes water levels have varied in the past, so how do we know whether climate change is a factor in the changes taking place now?
Precipitation increases in winter and spring are consistent with the fact that a warming atmosphere can transport more water vapor. Converting water from vapor to liquid and ice releases energy. As a result, increased atmospheric moisture contributes to more precipitation during extreme events. That is, when weather patterns are wet, they are very wet.
Flooding in New York state along the Lake Ontario shoreline, May 28, 2019.
Changes in seasonal cycles of snowmelt and runoff align with the fact that spring is coming earlier in a changing climate. Climate models project that this trend will continue. Similarly, rising lake temperatures contribute to increased evaporation. When weather patterns are dry, this produces lower lake levels.
Wet and dry periods are influenced by storm tracks, which are related to global-scale processes such as El Niño. Similarly, cold air outbreaks are related to the Arctic Oscillation and associated shifts in the polar jet stream. These global patterns often have indirect effects on Great Lakes weather. It is uncertain how these relationships will change as the planet warms.
Tools for better forecasts
Rapid changes in weather and water supply conditions across the Great Lakes and upper Midwest are already challenging water management policy, engineering infrastructure and human behavior. We are undoubtedly observing the effects of a warming climate in the Great Lakes, but many questions remain to be answered.
Soils in most of the Great Lakes states are extremely wet. For example, in 99th percentile zones, soil moisture is higher than 98% of the entire historical record. Credit: NOAA
The Great Lakes are, collectively, a critical water resource. Government agencies and weather forecasters need new tools to assess how future climate conditions may affect the Great Lakes water budget and water levels, along with better shorter-term forecasts that capture changing conditions.
Innovative techniques, such as incorporating information from snow and soil moisture maps into seasonal water supply forecasts, can help capture a full picture of what is happening to the water budget. The bigger point is that past conditions around the Great Lakes are not a reliable basis for decision-making that will carry into the future.
This article was originally published on The Conversation. Read the original article.
ABOUT THE AUTHOR(S)
Associate Professor of Environment and Sustainability, University of Michigan.
Professor of Climate and Space Sciences and Engineering, University of Michigan.