Low water level conditions continue on the Great Lakes
Toronto - December 6, 2000 - Water levels on three of the Great Lakes are at their lowest point for this time of year in several decades. There is no indication that this trend will change in the near future.
Lake Superior's level is at the lowest it has been for the beginning of December since 1925. It is 21 centimetres lower than it was one year ago and only 16 centimetres above its record low for this time of year. Lakes Michigan and Huron are at their lowest beginning of December levels since 1964, 16 centimetres lower than last year's levels, and 22 centimetres above record lows for the 20th century.
Water levels on the Great Lakes invariably decline during the fall and early winter. This is primarily due to high rates of evaporation at this time of year. However, Lake Superior's level has been falling faster than average during recent months and is currently 35 centimetres below average. There is no indication that the trend will reverse itself in the short term.
The levels of Lakes Michigan and Huron have been at least 45 centimetres below average since February. They have showed no signs of increasing towards average even though precipitation this year over their drainage basins has been about seven percent above average. Like Lake Superior, the levels of these lakes have been falling faster than average during recent months, and they are now 57 centimetres below average. High rates of evaporation and below average inflow from Lake Superior have more than offset the above average precipitation.
The continuing decline in Great Lakes water levels is causing commercial ships to carry lighter loads than during the summer. Further reductions in load will occur until navigation ceases for the winter in late December to early January. Low water levels may also cause problems for water intakes that are not designed to accommodate these conditions.
On a positive note, low water levels will significantly reduce the risk of flooding and storm damage to shoreline properties, particularly along the upper Great Lakes.
On the other Great Lakes, water levels are also low but not as far below average as on Superior, Michigan & Huron. Lake St. Clair is 21 centimetres below average, and four centimetres below the level of one year ago. Lakes Erie and Ontario are both about 10 centimetres below average and approximately the same as last year's levels. Precipitation over the drainage basins of these lakes has been 17 percent and eight percent, respectively, above average this year, which has compensated for below average water inflows from the upper lakes.
Rain, snowfall and regional air temperatures during the winter and spring will determine the water levels of the Great Lakes for next spring and summer. The seasonal forecast for the Great Lakes area issued by the Canadian Meteorological Centre suggests the probability of above average temperatures and below average precipitation for the winter months of December through February. Such conditions could lead to a steep decline in the levels of Lakes Erie and Ontario. It is expected that the levels of all the Great Lakes will remain below average for the next six months but still be above the extreme record low levels that were experienced in the 1920s, '30s and '60s. For Lakes Superior, Michigan and Huron, it is very likely that levels from December to May will be lower than they were during the corresponding months of the previous year.
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