Snow covering the Lake Michigan area on April 2, 2013.
Water levels in two of the Great Lakes dipped to record lows in January, but while spring conditions are expected to give these freshwater bodies a seasonal boost, scientists say the ability to forecast long-term trends remains difficult due to climate fluctuations.
"Our uncertainty on future water levels — which is considerable — is a direct reflection of our uncertainty on future climates," Drew Gronewold, a hydrologist at the National Oceanic and Atmospheric Administration's Great Lakes Environmental Research Laboratory in Ann Arbor, Mich., said in a news briefing today (April 23).
In January, average water levels in Lake Michigan and Lake Huron fell to 576.02 feet (175.57 meters), the lowest levels since 1964. Gronewold says these drops were largely due to warmer and dryer conditions the previous year, which produced less snowpack in the region.
Scientists monitor changes in the so-called Great Lakes water budget to make short- and long-term forecasts of water levels. This budget takes into account the water that comes into the Great Lakes basin through precipitation, ice cover and runoff, and the water that leaves through evaporation.
"The interplay between relative increases in precipitation and relative increases in evaporation are what will drive water levels," Gronewold said.
But, these calculations can be tricky because they incorporate so many different variables, including the effects of climate change, he added. Changes in solar energy, for example, which would increase or decrease evaporation, can affect how much rainfall eventually runs off into the lakes, or gets sent back into the atmosphere.
And whereas NOAA closely monitors the interplay between precipitation and evaporation for all the Great Lakes, Gronewold said it is difficult to know how these changes will play out over the next several decades.
In the meantime, the spring season may bring some short-term relief to the area. It is not unusual for springtime runoff, coupled with melting snowpacks, to contribute 5 inches (12.7 centimeters) to the lakes, Gronewold explained.
"This is a time of year when water levels typically rise naturally," Gronewold said.