Introduction

The Great Lakes region, for purposes of this paper, includes all of the Great Lakes drainage basin, and all of Minnesota, Wisconsin, and Michigan. The drainage basin includes portions of Ontario and Quebec, Canada, as well as portions of Minnesota, Wisconsin, Illinois, Indiana, Ohio, Pennsylvania, and New York, and all of Michigan. Since 1900, the population of this region has increased more than 4 fold -- from approximately 10 million to the present level of over 40 million. The importance of the region is related to the Lakes. The five Great Lakes -- Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario -- span more than 750 miles from east to west, cover more than 94 thousand square miles, and drain more than twice as much land. With about 5,500 cubic miles of fresh water, nearly 20% of the world's supply, the Great Lakes comprise the largest system of fresh surface water on our planet. In fact, only the polar ice caps contain more fresh water.

Weather in the Great Lakes Basin, the watershed area of the Great Lakes, is influenced by air masses from other regions, the location of the basin, and the moderating influence of the lakes themselves. Generally, air movement in the region is from west to east. However, the weather is highly variable because of the alternating flows of warm, humid air from the Gulf of Mexico and cold, dry air from the Arctic. Further, because this region is so large, its weather and vegetation can vary tremendously due to the synergistic (combination/enhanced) impacts of the air masses from other regions, the geographic location, and the moderating influence of the lakes.

For example, to the north and west (e.g., International Falls, MN), the climate is cold, has a large seasonal temperature range, and winter nighttime temperatures are typically subzero. Conifers, cone-bearing trees, dominate the northwestern forests. In the south and east (e.g., Detroit MI), it is warmer, experiences less range in temperatures, and has more annual and seasonally distributed precipitation than in the north and west. The original deciduous, or leaf-bearing, forests in the south and east have given way to agricultural and urban areas. The fertile soils of the southern area serve as prime agricultural land, some of the richest in the world.

Most of the basin of Lake Superior -- the largest and most westerly of the Great Lakes -- is forested, with little agriculture because of the basin's poor soils and cool climate. Harvesting of timber figures prominently in the economy of this area, with transportation of forestry products enhanced by easy access to this and other lakes.

Lake Michigan is the second largest of the lakes and the only one located completely within the United States. The northern part of the lake is colder and the area surrounding that part of the lake is sparsely populated, except for the Fox River valley that drains into Green Bay. Green Bay supports one of the most productive Great Lakes fisheries but also receives the wastes from the world's largest concentration of pulp and paper mills. The more temperate southern basin of Lake Michigan is among the most urbanized areas in the Great Lakes region. It is home to the Milwaukee and Chicago metropolitan areas and eight million people, or one-fifth of the total population of the Great Lakes Basin. Chicago, the largest financial and retailing center in this region, is the third largest city in the US.

Lake Huron, which frames northeastern Michigan, is the third largest of the Great Lakes by volume. Its Saginaw River basin is intensively farmed and is home to the Flint and Saginaw-Bay City metropolitan areas. Saginaw Bay, like Green Bay, contains a very productive fishery.

Lake Erie is the fourth largest of the Great Lakes and is the shallowest. It is partially icebound in the winter and is usually closed to navigation for about 4 months of the year. Lake Erie is bordered on the Canadian shore by rich agricultural lands and on both shores by numerous port cities whose economics have been based on heavy industry. Untreated industrial and municipal wastes from cities on both sides of the border contaminated the lake until those discharges were stopped in 1972. The environment has greatly recovered and now boasts numerous recreational facilities along the coasts in both the US and Canada. Detroit, the largest city in Michigan is located on the Detroit River (actually a strait) that connects Lake Erie to Lake St. Claire (to Lake Ontario). Detroit is the largest city in Michigan accommodating about 45% of the population and is also the state's largest port. Detroit is commonly known as the Automobile Center of the World or the Motor City because more automobiles are produced here than anywhere else in the US.

The smallest and lowest (in relation to sea level) of the Great Lakes is Lake Ontario. Oceangoing vessels from the upper Great Lakes reach Lake Ontario by way of the Welland Canal that by-passes Niagara Falls. Navigation of Lake Ontario is not usually impeded by winter ice. Lake Ontario is bordered by the Canadian cities of: St. Catherine's, Hamilton, Toronto, Oshawa, and Kingston; and the US cities of Rochester and Oswego, NY. While fishing is important, pollution has historically been a problem. Water quality is improving and recreational facilities are provided on both sides of the lake at state and provincial parks.

During the past century, temperatures in the Great Lakes region have changed, with warming of almost 4° F in the Upper Great Lakes (northern and western) areas. The opposite pattern typifies the southern portion of the region (along the Ohio River Valley), which has generally cooled by about 1° in the past century. Both upper and lower areas of this region are characterized by increasing annual precipitation, reaching as much as 10-20% increases over the 20^th century. Much of the precipitation has resulted from an increase in the number of days with occurrences of heavy to very heavy precipitation. There have also been significant increases in the number of days with excessive moisture in the eastern portion of the basin.

Possible Futures

Based on the results of global computer models, future climatic conditions for this region are projected to lead to increases in the typical low and the typical high temperatures, as well as increases in overall precipitation through the end of the 21^st century. Although these models are not as reliable at the regional level as at the global level, nonetheless the information can be used to help in identifying a region's vulnerabilities to climate change and to increase its preparation and resilience.

During the 21^st century, temperatures are expected to increase everywhere in this region. The rate of increase given by these model projections is larger than that observed in the 20^th century. Even over the northern portion of the region where warming has been the most pronounced -- the models project an increase in the warming of 5 to 10^oF in the 21^st century. The minimum temperature (e.g., winter or night time) is expected to increase more than the maximum, perhaps by 1 to 2^oF more over the century. Precipitation is likely to continue its upward trend, with 10-30% increases projected across much of the region.

In spite of the increases in precipitation, increases in temperature and changes in meteorological factors such as cloud cover and wind and biological factors such as evapotranspiration (the water given off by soil and plants) are expected to lead to a substantial increase in overall evaporation. This increase in evaporation is very likely to lead to a soil moisture deficit, reduction in lake and river levels, and more drought-like conditions in many areas. This overall drying is projected even though there are also likely to be increases in the frequency and intensity of heavy and very heavy precipitation events across the region. This will be occurring because a higher percentage of rain will be occurring on the 10% of days that already receive the most rain, so a higher percentage of the precipitation will be runoff rather than being available as soil moisture for plants.