The Great Lakes – which provide drinking water to nearly 20 million Americans – are suffering from a major drought.
An unusually dry September combined with the seasonal drop in water levels has caused water levels to fall between five and eight inches below normal.
For Lake Superior, Lake Michigan and Lake Huron, this is the lowest level since 2014.
The Great Lakes, which span eight states, account for 21 percent of the world’s fresh water, and 10 percent of the U.S. population depends on them for drinking water.
Lake Superior has seen the most drastic decline after receiving just 38 percent of the rain it normally receives in September.
On October 11, the water level for Lake Superior was 600 feet, which is six inches lower than the long-term average for October.
Above-average temperatures in September have also played a role in this drought, as the heat has increased the amount of evaporation from the Great Lakes.
30 million people live along the approximately 7,000 kilometer long coastline of the Great Lakes and depend on these lakes for their drinking water
The Great Lakes are the largest group of freshwater lakes in the world by total area, and the second largest by volume.
They include Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Pennsylvania and Wisconsin.
This isn’t the first time the Great Lakes have suffered from drought. In 2013, water levels fell to a historic low, after a year of record high temperatures in 2012.
This had a major impact on tourism, fishing, local businesses and other industries linked to the lakes, with many harbor masters forced to resort to dredging to keep their ports open.
Water levels could continue to drop until March, when spring rains and snowmelt provide some replenishment.
This corresponds to a seasonal decline that begins around September each year and lasts until early spring.
The Great Lakes depend on precipitation for replenishment. Each lake is surrounded by a drainage basin – an area of land where water from rain or melting snow drains downhill into a body of water (in this case, the lake).
Of the five lakes, Lake Superior received the least amount of rain in September, receiving just 38 percent of normal precipitation. MLive.com reported.
The Great Lakes are the largest group of freshwater lakes in the world by total area, and the second largest by volume
This is the longest Lake Superior water levels have remained below the September monthly average since 2014.
Lake Michigan and Lake Huron – which are considered one lake when discussing water levels – also fell below the September monthly average for the first time since 2014.
In September of this year, the Lake Michigan-Huron basin experienced hot, dry temperatures that increased evaporation, and only 1.5 inches of rain fell – just 44 percent of the precipitation that normally falls.
Lake Ontario’s water level fluctuates the most of the five Great Lakes. That’s mainly because dams control some of the outflow from this lake to the St. Lawrence Seaway.
Currently, this lake is at its long-term average water level for September, and is expected to remain near normal for the next six months.
Although Lake Ontario received the most rainfall in September, it still received only 80 percent of normal rainfall.
Lake Erie’s water level is currently about eight inches higher than the long-term average for September, but still received only 55 percent of normal rainfall that month. The water levels of this lake have remained normal since March 2015.
Climate scientists use Great Lakes water levels as an indicator of climate change because their fluctuations are directly affected by changing weather patterns.
According to Michigan Technological University, water levels in the Great Lakes have undergone dramatic fluctuations in recent decades, ranging more than 6 feet.
Water levels are determined by climate-induced changes in three major factors: lake precipitation, lake evaporation, and basin discharge.
Climate change has a direct effect on all three of these factors. In the short term, rising temperatures linked to global warming make droughts like this more likely.
But in the long term, scientists have predicted that climate change could cause Great Lakes water levels to rise over the next three decades.
According to one study, lake base levels for Lake Superior, Michigan-Huron and Erie are expected to rise by about 8 to 8 inches by 2050 due to increasing precipitation due to climate change.
This could cause serious problems for the more than 30 million people who live along the lakes’ approximately 4,500 miles of coastline, including densely populated cities such as Chicago, Detroit and Buffalo.
Previous cases of record high water levels in the Great Lakes have already shown how the resulting flooding can wreak havoc on infrastructure, communities and ecosystems.