52

KEY ISSUES

arming,manufacturing,and forestry characterize the Midwest. The Great

Lakes form the world's largest freshwater lake system,providing a major

recreation area as well as a regional water transportation system with

access to the Atlantic Ocean via the St.Lawrence Seaway. The region

encompasses the headwaters and upper basin of the Mississippi River

and most of the length of the Ohio River, both critical water sources

and means of industrial transportation providing an outlet to the Gulf of

Mexico. The Midwest contains some of the richest farmland in the

world and produces most of the Nation's corn and soybeans. It also has

important metropolitan centers,including Chicago and Detroit. Most of the largest

urban areas in the region are found along the Great Lakes and major rivers. The

"North Woods" are a large source of forestry products and have the advantage of

being situated near the Great Lakes,providing for easy transportation.

Observed Climate Trends

ver the 20th century, the northern portion of the Midwest,including the

upper Great Lakes,has warmed by almost 4oF (2oC),while the southern portion,along the Ohio River valley, has cooled by about 1oF (0.5oC). Annual precipitation has increased,with many of the changes quite substantial,including as much as

10 to 20% increases over the 20th centur y. Much of the precipitation has resulted

from an increased rise in the number of days with heavy and very heavy precipitation events. There have been moderate to very large increases in the number of

days with excessive moisture in the eastern portion of the basin.

Scenarios of Future Climate

uring the 21st century, models project that temperatures will increase

throughout the Midwest,and at a greater rate than has been observed in the

20th century. Even over the northern portion of the region,where warming has

been the largest,an accelerated warming trend is projected for the 21st century,

with temperatures increasing by 5 to 10oF (3 to 6oC). The average minimum temperature is likely to increase as much as 1 to 2oF (0.5 to 1oC) more than the maximum temperature. Precipitation is likely to continue its upward trend,at a slightly

accelerated rate;10 to 30% increases are projected across much of the region.

Despite the increases in precipitation,increases in temperature and other meteorological factors are likely to lead to a substantial increase in evaporation,causing a

soil moisture deficit, reduction in lake and river levels,and more drought-like conditions in much of the region. In addition,increases in the proportion of precipitation coming from heavy and extreme precipitation are very likely.

• Reduction in Lake and

River Levels

• Health and Quality of Life

in Urban Areas

• Agricultural Shifts

• Changes in Semi-natural

and Natural Ecosystems

Climate Extremes Create

Critical Transportation

Problems

Climate extremes in the Midwest can drastically impede the highly weather-sensitive

transportation systems that serve not only

the region, but the entire nation. Chicago is

the nation's rail hub handling much of the

nation freight traffic. Barges operating on

the Mississippi River system, that includes

the Ohio, Illinois, and Missouri Rivers, handle a large fraction of the country’s bulk

commodities, such as grain and coal.

Prolonged heavy rainfall in the spring and

summer of 1993 produced extensive flooding across nine states in the upper Midwest.

The flood waters poured over and through

many levees and inundated numerous

floodplains that many of the key rail lines

cross. The flood waters became an 

F

O

D

MIDWEST
Temperature Change - 20th & 21st Centuries

53

An accelerated warming trend is projected for the 21st century, with temperatures increasing by 5 to 10 ̊F (3 to 6 ̊C).

Precipitation is likely to continue its upward trend, at a

slightly accelerated rate; 10 to 30% increases are projected

across much of the region.

absolute barrier to surface transportation in

the region for more than six weeks. Train

traffic had to be rerouted around the flood

area, resulting in long delays and large

costs to manufacturing. River barge traffic

suffered a similar fate with the additional

costs to shipping and manufacturing

approaching $2 billion. 

This came on the heels of the 1988

drought that also had a major impact on

barge shipping due to low river levels, illustrating the sensitivity of transportation systems to both wet and dry climate extremes.

Precipitation Change - 20th & 21st Centuries

Observed 20th Canadian Model 21st

The Hadley model indicates

that this trend will continue,

resulting in increases of

about 25% from the present.

The Canadian model suggests

that these increases will be

confined to the northern and

western parts of the region.

On average,

Midwest

precipitation over

the 20th

century has

increased. 

100%

75%

50%

25%

0

-25%

-50%

-75%

-100%

100%

80%

60%

40%

20%

0

-20%

-40%

-60%

-80%

-100%

Hadley Model 21st

Canadian Model Hadley Model

Both climate models indicate that the northern part of the

Midwest will experience the largest increases in winter

temperatures. The Canadian Model suggests the greatest

increases, approaching 15oF in Minnesota and the Upper

Peninsula of Michigan. 

Winter Minimum Temperature Change

21st Century Average

+15oF

+10oF

+5oF

0o

-5oF

Observed 20th

Canadian Model 21st Hadley Model 21st

Temperatures in the Midwest have

increased, with the largest observed

changes for the region in Minnesota

and the Upper Peninsula of Michigan.

Model scenarios suggest further

increases over the 21st century from

near 5oF (Hadley model) to more than

10oF (Canadian model). 

+15oF

+10oF

+5oF

0o

-5oF

+15oF

+10oF

+5oF

0o

-5oF

+15oF

+10oF

+5oF

0o

-5oF
Reduction in Lake and River Levels

ater levels,supply, quality, and water-based transportation and recreation

are all climate-sensitive issues affecting the region. Despite the projected increase in precipitation,increased evaporation due to higher summer air

temperatures is likely to lead to reduced levels in the Great Lakes.Of 12 models

used to assess this question,11 suggest significant decreases in lake levels while

one suggests a small increase. The total range of the 11 models' projections is

less than a one-foot increase to more than a five-foot decrease. A five-foot (1.5-

meter) reduction would lead to a 20 to 40% reduction in outflow to the St.

Lawrence Seaway. Lower lake levels cause reduced hydropower generation

downstream,with reductions of up to 15% by 2050. An increase in demand for

water across the region at the same time as net flows decrease is of particular

concern. There is a possibility of increased national and international tension

related to increased pressure for water diversions from the Lakes as demands

for water increase. For smaller lakes and rivers, reduced flows are likely to

cause water quality issues to become more acute. In addition,the projected

increase in very heavy precipitation events will likely lead to increased flash

flooding and worsen agricultural and other non-point source pollution as more

frequent heavy rains wash pollutants into rivers and lakes. Lower water levels

are likely to make water-based transportation more difficult with increases in

the costs of navigation of 5 to 40%. Some of this increase will likely be offset as

reduced ice cover extends the navigation season. Shoreline damage due to

high lake levels is likely to decrease 40 to 80% due to reduced water levels.

Adaptations: A reduction in lake and river levels would require adaptations

such as re-engineering of ship docks and locks for transportation and recreation. If flows decrease while demand increases,international commissions

focusing on Great Lakes water issues are likely to become even more important

in the future.Improved forecasts and warnings of extreme precipitation events

could help reduce some related impacts.

54

MIDWEST KEY ISSUES

W

0

30

60

90

120

150

180

1850 1900 1950 2000

Lake ice duration has decreased by

nearly one month over the past 150

years, with a record low in the winter

of 1997-98. This is consistent with

observed increases in temperature.

Lake Ice Duration at Lake Mendota

Madison, Wisconsin

142 Years (1856 - 1998)

The projected increase in

very heavy precipitation

events will likely worsen

agricultural and other nonpoint source pollution as

more frequent heavy rains

wash pollutants into rivers

and lakes.

Lower water levels are likely

to make water-based transportation more difficult with

increases in the costs of

navigation of 5 to 40%. 
Health and Quality of Life in Urban Areas

reduction in extremely low temperatures and an increase in extremely

high temperatures are expected. Thus,a reduced risk of life-threatening

cold and an increased risk of life-threatening heat are likely to accompany

warming. Reduced expenditures on snow and ice removal and fewer snow and

ice related accidents and delays are likely. During the summer, however, in

cities,heat-related stresses are very likely to be exacerbated by the urban heat

island effect,a phenomenon in which cities remain much warmer than surrounding rural areas. This elevates nighttime temperatures,and in combination

with the greater expected rise of nighttime temperatures compared to those of

daytime,there will be less relief at night during heat waves. Elevated nighttime

temperatures were a notable characteristic of the 1995 heat wave that resulted

in over 700 deaths in Chicago. In addition,during heat waves in the Midwest,

air pollutants are trapped near the surface,as atmospheric ventilation is

reduced. Without strict attention to regional emissions of air pollutants,the

undesirable combination of extreme heat and unhealthy air quality is likely to

result. There is also a possibility of an increased risk of water-borne diseases

with increases in extreme precipitation events,and increased insect- or tickborne diseases,such as St.Louis encephalitis. Recreational activities will very

likely shift as cold-season recreation such as skiing,snowmobiling,ice skating,

and ice-fishing,are reduced,and warm-season recreation such as swimming,hiking,and golf, are expanded,although during mid-summer, these activities are

likely to be affected by excessive heat.

Adaptations: Active responses,such as those taken by Chicago during the 1999

heat wave,are likely to help reduce the death toll due to extreme heat.

Separate storm water and sewer lines and other appropriate preventative measures can help mitigate the possible increased risk of water-borne diseases.

55

Canadian Model Hadley Model

A

Summer Precipitation

Summer Average Temperature

Illustration of how the summer climate of Illinois would shift under the Canadian and Hadley model scenarios. Under the Canadian

scenario, the summer climate of Illinois would become more like the current climate of southern Missouri in 2030 and more like

Oklahoma's current climate in 2090. The primary difference in the resulting climates of the two models relates to the amount of summer rainfall.

During the summer, in cities,

heat-related stresses are

very likely to be exacerbated

by the urban heat island

effect, a phenomenon in

which cities remain much

warmer than surrounding

rural areas. 

Elevated nighttime temperatures were a notable characteristic of the 1995 heat

wave that resulted in over

700 deaths in Chicago.
MIDWEST KEY ISSUES

Agricultural Shifts

griculture is of vital importance

to this region,the nation,and

the world. It has exhibited a capacity

to adapt to moderate differences in

growing season climate,and it is likely that agriculture would be able to

continue to adapt. With an increase

in the length of the growing season,

double cropping,the practice of

planting a second crop after the first

is harvested,is likely to become more

prevalent. The CO2fertilization effect

is likely to enhance plant growth and

contribute to generally higher yields.

The largest increases are projected to

occur in the northern areas of the

region,where crop yields are currently temperature limited. However,

yields are not likely to increase in all

parts of the region. For example,in

the southern portions of Indiana and

Illinois,corn yields are likely to

decline,with 10-20% decreases projected in some locations. Consumers

are likely to pay lower prices due to

generally increased yields,while most

producers are likely to suffer reduced

profits due to declining prices.

Increased use of pesticides and herbicides are very likely to be required

and to present new challenges.

Adaptations: Plant breeding programs can use skilled climate predictions to aid in breeding new varieties

for the new growing conditions.

Farmers can then choose varieties

that are better attuned to the expected climate. It is likely that plant

breeders will need to use all the tools

of plant breeding,including genetic

engineering,in adapting to climate

change.Changing planting and harvest dates and planting densities,and

using integrated pest management,

conservation tillage,and new farm

technologies are additional options.

There is also the potential for shifting

or expanding the area where certain

crops are grown if climate conditions

become more favorable. Weather

conditions during the growing season

are the primary factor in year-to-year

differences in corn and soybean

yields. Droughts and floods result in

large yield reductions;severe

droughts,like the drought of 1988,

cause yield reductions of over 30%.

Reliable seasonal forecasts are likely

to help farmers adjust their practices

from year to year to respond to such

events.

56

Midwest Soybean Yield and Precipitation 

The relationship between

Midwest soybean yield and precipitation is shown here.

Soybean yields in thousands of

bushels are shown as the differences from the average yield in

recent decades. Precipitation is

the difference from the 1961-90

average precipitation. Note that

lower yields result from both

extreme wet and extreme dry

conditions.

A

Farm flooded by Mississippi river in 1993.

2.0

1.9

1.8

1.7

1.6

1.5

1.4

1.3

1.2

1.1

1.0

0.9

0.8

0.7

8

6

4

2

0

-2

-4

-6

-8

1975 1980 1985 1990 1995
Changes in Semi-natural and

Natural Ecosystems

he upper Midwest has a unique

combination of soil and climate

that allows for abundant coniferous

tree growth. Higher temperatures

and increased evaporation will likely

reduce boreal forest acreage,and

make current forestlands more susceptible to pests and diseases. It is

likely that the southern transition

zone of the boreal forest will be susceptible to expansion of temperate

forests, which in turn will have to

compete with other land use pressures. However, warmer weather

(coupled with beneficial effects of

increased CO2),are likely to lead to

an increase in tree growth rates on

marginal forestlands that are currently temperature-limited. Most climate

models indicate that higher air temperatures will cause greater evaporation and hence reduced soil moisture,

a situation conducive to forest fires.

As the 21st century progresses,there

will be an increased likelihood of

greater environmental stress on both

deciduous and coniferous trees,making them susceptible to disease and

pest infestation,likely resulting in

increased tree mortality.

As water temperatures in lakes

increase,major changes in freshwater

ecosystems will very likely occur,

such as a shift from cold water fish

species,such as trout,to warmer

water species,such as bass and catfish. Warmer water is also likely to

create an environment more susceptible to invasions by non-native

species. Runoff of excess nutrients

(such as nitrogen and phosphorus

from fertilizer) into lakes and rivers is

likely to increase due to the increase

in heavy precipitation events. This,

coupled with warmer lake temperatures,is likely to stimulate the

growth of algae,depleting the water

of oxygen to the detriment of other

living things. Declining lake levels

are likely to cause large impacts to

the current distribution of wetlands.

There is some chance that some wetlands could gradually migrate,but in

areas where their migration is limited

by the topography, they would disappear. Changes in bird populations

and other native wildlife have already

been linked to increasing temperatures and more changes are likely in

the future. Wildlife populations are

particularly susceptible to climate

extremes due to the effects of

drought on their food sources.

57

-20

-10

0

10

20

30

40

50

60

Percentiles

Light

Moderate

Heavy

-10

0

10

20

30

40

50

60

Percentiles

Light

Moderate

Heavy

Canadian Model Hadley Model 

Projected Midwest Daily Precipitation

21st Century

Annual trends in daily precipitation by percentile for the Canadian and Hadley model scenarios

for the 21st century. Notice the largest trend is in the heaviest daily precipitation amount for

both model simulations, indicating that most of the projected increase in annual precipitation

will be due to an increase in precipitation on days already receiving large amounts.

T

Runoff of excess

nutrients (such as

nitrogen and phosphorus from fertilizer)

into lakes and rivers

is likely to increase

due to the increase in

heavy precipitation

events.

Lightest 5% 

Moderate Moderate

Heaviest 5% 

Lightest 5% 

Heaviest 5% 

Days receiving precipitation, sorted by percentile.