|National Water Availability and Use Program|
U.S. Geological Survey Scientific Investigations Report 2007–5118
By Glenn A. Hodgkins, Robert W. Dudley, and Stephen S. Aichele
This report is available below as a 37-page PDF for viewing and printing.
The total amount of water in the Great Lakes Basin is important in the long-term allocation of water to human use and to riparian and aquatic ecosystems. The water available during low-flow periods is particularly important because the short-term demands for the water can exceed the supply.
Precipitation increased over the last 90 years in the U.S. Great Lakes Basin. Total annual precipitation increased by 4.5 inches from 1915 to 2004 (based on the average of 34 U.S. Historical Climatology Network stations), 3.5 inches from 1935 to 2004 (average of 34 stations), and 4.2 inches from 1955 to 2004 (average of 37 stations). Variability in precipitation from year to year was large, but there were numerous years with relatively low precipitation in the 1930s and 1960s and many years with relatively high precipitation after about 1970.
Annual runoff increased over the last 50 years in the U.S. Great Lakes Basin. Mean annual runoff increased by 2.6 inches, based on the average of 43 U.S. Geological Survey streamflow-gaging stations from 1955 to 2004 on streams that were relatively free of human influences. Variability in runoff from year to year was large, but on average runoff was relatively low from 1955 to about 1970 and relatively high from about 1970 to 1995. Runoff increased at all stations in the basin except in and near the Upper Peninsula of Michigan, where relatively small runoff decreases occurred. Changes in annual runoff for the 16 stations with data from 1935 to 2004 were similar to the changes from 1955 to 2004. The mean annual 7-day low runoff (the lowest annual average of 7 consecutive days of runoff) increased from 1955 to 2004 by 0.048 cubic feet per second per square mile based on the average of 27 stations.
Runoff in the U.S. Great Lakes Basin from 1955 to 2004 increased for all months except April. November through January and July precipitation and runoff increased by similar amounts. There were differences between precipitation and runoff changes for February, March, and April, which were likely due to lower ratios of snowfall to rain and earlier snowmelt runoff in recent years. Increases in precipitation were larger than increases in runoff for May, June, August, September, and October. Some of this difference could be due to the different locations of the precipitation and streamflow stations in the basin. Part of the difference may be explained by changes in evapotranspiration.
Some of the few highly urbanized and highly regulated stations analyzed in this report had larger increases in annual 7-day low-runoff from 1955 to 2004 than any of the stations in the U.S. Great Lakes Basin that are on streams relatively free of human influences. This demonstrates the human influence over time on very low streamflows.
Changes—even over periods as long as 90 years—can be part of longer cycles. Previous studies of Great Lakes Basin precipitation and St. Lawrence River streamflow, using data from the mid-1800s to the late-1900s, showed low precipitation and streamflow in the late 1800s and early 1900s relative to earlier and later periods.
Purpose and Scope
Previous Studies of Streamflow and Precipitation Changes in the Great Lakes Basin
Physical Description of the Great Lakes Basin
Climate of the Great Lakes Basin in the United States
Streamflow and Meteorological Data and Analysis
Selection of Stations
Calculation of Statistics
Calculation of Basin Land Use
Calculation of Basin Population
Streams Relatively Free of Human Influences
Comparison of Streamflow Changes and Precipitation Changes
Relation of Low-Flow Changes to Agricultural Land Use
Highly Urbanized Streams
Highly Regulated Streams
Long-Term Perspective on Precipitation and Streamflow Changes
Summary and Conclusions
|1.||Map showing drainage area of the Great Lakes Basin, United States and Canada.|
|2.||Graph showing total annual precipitation for the average of 34 stations in the U.S. Great Lakes Basin, 1915–2004.|
|3.||Maps showing changes in annual precipitation, by station, for 1915–2004, 1935–2004, and 1955–2004.|
|4.||Maps showing changes in monthly precipitation, by station, 1955–2004.|
|5.||Graph showing annual runoff for the average of 43 stations in the U.S. Great Lakes Basin, 1955–2004.|
|6.||Maps showing changes in annual runoff, by station, for 1955–2004 and 1935–2004.|
|7.||Maps showing trends in monthly runoff, by station, 1955–2004.|
|8.||Map showing changes in annual 7-day low runoff, by station, 1955–2004.|
|9.||Graph showing relation between annual 7-day low runoff change, 1955–2004, and agricultural land use for 27 basins in the U.S. Great Lakes Basin.|
|10.||Graph showing annual 7-day low runoff for River Rouge at Detroit, Michigan, 1955–2004.|
|1.||Annual precipitation changes in the U.S. Great Lakes Basin, 1915–2004.|
|2.||Annual precipitation changes in the U.S. Great Lakes Basin, 1935–2004.|
|3.||Annual precipitation changes in the U.S. Great Lakes Basin, 1955–2004.|
|4.||Monthly precipitation changes in the U.S. Great Lakes Basin for 1915–2004, 1935–2004, and 1955–2004.|
|5.||Monthly precipitation changes in the U.S. Great Lakes Basin, 1955–2004.|
|6.||Mean annual runoff changes in the U.S. Great Lakes Basin, 1955–2004.|
|7.||Mean annual runoff changes in the U.S. Great Lakes basin, 1935–2004.|
|8.||Mean monthly runoff changes in the U.S. Great Lakes Basin, 1955–2004.|
|9A.||January through June monthly runoff changes in the U.S. Great Lakes Basin, 1955–2004.|
|9B.||July through December monthly runoff and annual 7-day low runoff changes in the U.S. Great Lakes Basin, 1955–2004.|
|10.||Mean monthly precipitation and runoff changes in the U.S. Great Lakes Basin, 1955–2004.|
|11.||Mean annual runoff and mean 7-day low-flow changes for a highly urbanized stream in the U.S. Great Lakes Basin, 1955–2004.|
|12.||Mean annual runoff and mean 7-day low-flow changes for highly regulated streams in the U.S. Great Lakes Basin, 1955–2004.|
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Hodgkins, G.A., Dudley, R.W., and Aichele, S.S., 2007, Historical changes in precipitation and streamflow in the U.S. Great Lakes Basin, 1915–2004: U.S. Geological Survey Scientific Investigations Report 2007–5118, 31 p.
For more information about USGS activities of the USGS National Water Availability and Use Program in the Great Lakes Region, see USGS Fact Sheet 2005-3113.
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