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Chicago
Pilot Cities
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definition
The City of Chicago is located on Lake Michigan in northeast Illinois. The city has a population of approximately three million people and covers over 225 square miles. The Chicago metropolitan region includes more than 7 million people in a six-county area and covers approximately 3,750 square miles.
Chicago's Heat Island
In 1999, researchers from Northwestern University used data from the National Climatic Data Center (NCDC) to identify the location of Chicago's heat island. They collected data from locations in Chicago that corresponded to ground-level ozone monitoring so that the relationship between ozone and temperature could be evaluated.
The researchers found that the Chicago heat island consistently appears in the western suburbs, not in the core downtown area. Lake Michigan, to a great extent, influences Chicago's climate. Further, the western suburbs are developing rapidly. The temperature gradient between areas in the far west suburbs and downtown Chicago is on average 3-5°F (1.7-2.8°C).
Before determining how heat island reduction strategies impact an area, researchers need to evaluate existing surface characteristics of the area. Aerial photos are useful for estimating the proportions of vegetative, roofed, and paved surface cover relative to the total urban surface in a city. Having this urban fabric information can help researchers simulate the meteorological and air quality impacts of heat island reduction strategies.
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Chicago's Climate
Chicago's climate is predominantly continental, ranging from warm in the summer to cold in the winter. Its climate is partially modified by Lake Michigan, and to a lesser extent by other Great Lakes.
The flat terrain of the Midwest and Lake Michigan make Chicago's weather unpredictable and frequently extreme. Summer is very warm and often humid. The highest temperatures occur throughout July and August and can reach 95-100°F (35-38°C). The coldest days are usually in January when the temperature can drop below 0°F (-18°C). Average monthly temperatures for Chicago range from 21°F (-6°C) in January to 73°F (23°C) in July.
Chicago receives an average annual rainfall of 31.7
inches per year and has an average relative humidity of
80% in the morning and 62% in the afternoon. Based on
1961-1990 NCDC data, Chicago has, on average, 752
cooling degree
days
and 6,536
heating degree
days
.
Local climate data, such as cooling and heating degree days, can help researchers estimate the potential energy savings and air quality impacts of heat island reduction strategies. For example, areas with long, sunny, hot summers and high cooling degree day values, generally can achieve substantial energy savings.
Information on an area's local climate can also help
communities focus on heat island reduction activities
that best suit their region. For example, cities with
predominantly dry climates may achieve greater benefits
from increasing vegetation than would cities in humid
climates. Dry-climate cities more effectively capture
the cooling benefits of evapotranspiration – or
evaporation of water from leaves. However, dry-climate
cities also need to consider the availability and cost
of water to maintain vegetation.