Lake LevelsFebruary 10th, 2013 at 2:00 am by Bill Steffen under Bill's Blog, Weather
The first image is the MODIS Great Lakes satellite image from Weds. (Feb. 6). You can see ice in Green Bay, some ice east of Chicago and there is ice up toward the Mac Bridge. There’s a fair amount of ice on Saginaw Bay and on Lake Erie, which despite being the Great Lake that is farthest south, often has the highest percentage of surface ice cover of any of the Great Lakes because it’s the shallowest of the Great Lakes. The second image from NOAA (here’s another image) shows Great Lakes ice as we enter the 2nd week of February. You probably heard that Lake Michigan has reached it’s lowest water level since records began in 1918. The article cited “USACE (Army Corps of Engineers) says below-average snowfall last winter, combined with a hot dry summer, contributed to more evaporation and the record low levels”. Let’s explore that statement a little. Lake Michigan is down 15″ in the past year. Season snowfall last year in G.R. was 51.2″, below the current average of 74″ (that average went UP 2″ when the new 30-year averages were implemented (1981-2010)…the decade of the 2000s was the snowiest decade EVER in G.R.). First, with a snow/water equivalent of 15 to 1, that would only amount for a 2″ drop (assuming that the watershed had similar low snowfall totals) on the lake, not 15″. However, we shouldn’t look at snowfall. A better measure would be total precipitation (rain and snow). If we had below average snowfall, but above average rainfall – then Lake Michigan’s water level would probably go UP instead of down and you couldn’t blame a substantial loss of water like that on a lack of snowfall…well…read on.
Precipitation for G.R. was ABOVE AVERAGE in G.R. in December 2011 AND in January, February and March of 2012. Yeah, it was dry during the summer, but on those really hot days in July, look at how light the wind was. With calm or very light winds, a cooler layer of air with higher relative humidity would have been sitting over the lake water. Also, precipitation for Grand Rapids over the last 2 years has been ABOVE AVERAGE. Precipitation in 2012 for G.R. was 33.85″. That was 4.42″ below the 1981-2010 average of 38.85″ (or 88.45% of average). Precipitation in 2011 for G.R. was 45.09″ or 6.82″ ABOVE average (or 116% of average). That average precipitation for G.R. has been increasing. The average we used for G.R. from the 1941-1970 data was 32.39″. Part of the increase is changes in land use. We have now planted the Midwest in corn and soybeans and yields have increased as we now plant individual plants very close together. I’ve talked before about transpiring corn and soybeans and how much water they can add to the air. If you’re old enough to remember corn fields back in the 1950s you’ll know that they plant corn plants much closer to each other now than they did back then. Look at the graph on this page and you can see the increase in yield per acre. Even in a drought year like last year, the average yield per acre is higher than it was for any year back in the 1980s. Side note, the Texas State Climatologist, Dr. John Nielsen-Gammon states in this article that “There is no evidence that climate change contributed to the lack of rainfall, because rainfall has risen over the past century…” If you look at the 2012 Climate Summary for Muskegon, the average wind speed was 8.9 mph and the average humidity was 67%. This chart from the National Climate Data Center gives an average annual relative humidity for Muskegon of 64% (lower than last year). Now, Muskegon is just one location. I don’t have time to do a detailed study on the Lake Michigan/Lake Huron Watershed. About 30% of the equation for the later level of Lake Michigan/Huron (for lake-level purposes these 2 lakes are really one big lake, connected at the Mac. Bridge) is water that comes down the St. Mary’s River from Lake Superior. Lake Superior’s water level has not dropped like Lake Michigan/Huron, as it’s unchanged from one year ago (compared to the 15-inch drop in Lake Michigan/Huron). You may also see in related articles that Lake Erie has also dropped quite a bit (down 20″ in the past year). That’s true, but Lake Erie fluctuates to a much greater degree than Lakes Michigan, Huron or Superior. Lake Erie is only 4″ below average water level, which means with a 20″ drop, it was actually 16″ above average one year ago.
So, let’s look elsewhere. Read this article from the Milwaukee Journal. The first sentence says: “Pressure is mounting on the U.S. and Canadian governments to explore ways to restore water levels on Lakes Michigan and Huron that have been lowered nearly two feet due to historic dredging on the St. Clair River.” Again that’s “…due to historic dredging on the St. Clair River.” The article also says: “the federal government has long acknowledged that this human meddling in the riverbed has led to a permanent drop of about 16 inches from Michigan and Huron’s long-term average.” and “…a Canadian conservation group created by property owners from northern Lake Huron’s Georgian Bay hired its own engineering firm to conduct a study of what was going on in the St. Clair River back in 2004. That study said the water lost from the lakes by expanding the river channel was actually much greater than 16 inches – and getting worse.” Thanks to Dan Egan for the work he did on this article. He went beyond just retyping a press release. While some are blaming lower snowfall for a single winter or the general “climate change” for the 15″ drop in a year of Lake Michigan’s water level, maybe that’s only part of the answer, or not the answer at all.
While, I’m at it…one more point. Look at this climate page from the GRR NWS. This is a comparison of the 1971-2000 30-year climate averages for Grand Rapids and the current 1981-2010 climate averages. Look at snowfall. The average snowfall for Grand Rapids went up! By eliminating the 1970s and adding the 2000s, the average snowfall increased from 72.2″ to 74.9″. People my age remember the big blizzard of 1978 and the cold winters from 1976 to 1979 when we had few thaws and the snow hung around longer. However, those winters were not average. The winter of 1976-77 was the coldest winter in G.R. in the last 100 years. The following winter we had the big Blizzard of ’78, followed by the coldest February and the 5th coldest March ever…and in 1979, Lake Michigan pretty much froze over. That was an unusual trio of cold winters, not average winters. While we were below average for snowfall last winter, that’s hardly been the trend. I wish I had more time to study this issue myself. I grew up about two miles from Lake Michigan and I remember the low water of the mid 1960s and the high water of 1986-1987. The water level of a lake like Lake Michigan is a complicated conglomerate of many different variables. The below average snowfall of last winter does not explain a 15-inch drop in the water level of Lake Michigan.