Illinois State Water Survey - University of Illinois at Urbana-Champaign

State Climatologist Office for Illinois

The 1995 Heat Wave in Chicago, Illinois

Dr. Jim Angel, State Climatologist

The heat wave in July 1995 in Chicago was one of the worst weather-related disasters in Illinois history with over 700 deaths over a 5-day period. According to the National Weather Service, "Heat is the number one weather-related killer in the United States, resulting in hundreds of fatalities each year. In fact, on average excessive heat claims more lives each year than floods, lightning, tornadoes, and hurricanes combined."

Why was the July 1995 event so severe?

Here are the records for Chicago at Midway airport:

STATION: CHICAGO_MIDWAY_AP_3_SW, IL   (Station ID: 111577)

            Precip-  |<--temperature->|          Snow  Snow
            itation  High    Low   Mean  Degree  Fall  Depth Observe
Year Mo Dy   (in)    (F)     (F)   (F)    Days   (in)   (in)   Time  Source
1995 07 01   0.00     77     60     69      4     0.0     0     MID     F
1995 07 02   0.00     78     57     68      3     0.0     0     MID     F
1995 07 03   0.00     83     63     73      8     0.0     0     MID     F
1995 07 04   0.28     86     69     78     13     0.0     0     MID     F
1995 07 05   0.09     87     67     77     12     0.0     0     MID     F
1995 07 06   0.00     81     69     75     10     0.0     0     MID     F
1995 07 07   0.00     81     63     72      7     0.0     0     MID     F
1995 07 08   0.00     84     60     72      7     0.0     0     MID     F
1995 07 09   0.04     85     66     76     11     0.0     0     MID     F
1995 07 10   0.00     90     64     77     12     0.0     0     MID     F
1995 07 11   0.00     90     73     82     17     0.0     0     MID     F
1995 07 12   0.00     98     76     87     22     0.0     0     MID     F
1995 07 13   0.00    106     81     94     29     0.0     0     MID     F
1995 07 14   0.00    102     84     93     28     0.0     0     MID     F
1995 07 15   0.47     99     77     88     23     0.0     0     MID     F
1995 07 16   0.00     94     76     85     20     0.0     0     MID     F
1995 07 17   0.00     89     73     81     16     0.0     0     MID     F

The really hot weather occurred from July 12 to July 16. The 106° F on July 13th set the record for the warmest July temperature since records began at Midway in 1928. Not only were the daytime temperatures high but the nighttime low temperatures were quite high (upper 70s and lower 80s) as well. Record humidity levels also accompanied the hot weather. The high humidity and high nighttime temperatures provided little relief from the heat.

Urban Heat Island

Another contributing factor in the heat wave is the so-called "urban heat island". Urban heat islands are caused by the high concentration of buildings, parking lots, and roads in urban areas, which tend to absorb more heat in the day and radiate more heat at night than comparable rural sites. Therefore, urban areas usually experience a lot less cooling at night than do rural sites. Furthermore, temperature measurements at O’Hare Airport, a more suburban site, will not reflect the severity of the 1995 heat wave in the inner city.

Most of the victims of the 1995 heat wave were the elderly in the heart of the urban area. Many of the poorer older citizens either had no air conditioning or could not afford to operate the system they had. Many older citizens were also hesitant to open windows and doors at night for fear of crime. By contrast, in the heat waves of the 1930s, many residents slept outside in the parks or along the shore of Lake Michigan.

Other factors that contributed to the high number of deaths were an inadequate local heat wave warning system, power failures, inadequate ambulance service and hospital facilities, and the aging of the population in the urban areas. City officials did not release a heat emergency warning until June 15, the last day of the heat wave. Thus, such emergency measures as Chicago’s five cooling centers were not fully utilized. The medical system of Chicago was severely taxed as thousands were taken to local hospitals with heat-related problems. In some cases, fire trucks were used as substitute ambulances.

Unfortunately, Chicago will continue to be vulnerable to heat waves because of the urban heat island and the socio-economic makeup of the urban area (high percentage of lower-income elderly). However, the number of deaths may be reduced by: a) implementing an early-warning system that takes into account the local conditions, b) better define the heat island conditions associated with heat waves to improve forecasts, c) develop a uniform means for classifying heat-related deaths, and d) increase the research on the conditions of heat stress and heat waves.

For further reading:

Changnon, S. A., K. E. Kunkel, and B. C. Reinke, 1996: Impacts and Responses to the 1995 Heat Wave: A Call to Action. Bulletin of the American Meteorological Society, Vol. 77, No. 7, 1497-1506.

Kunkel, K. E., S. A. Changnon, B. C. Reinke, and R. W. Arritt, 1996: The July 1995 Heat Wave in the Midwest: A Climatic Perspective and Critical Weather Factors. Bulletin of the American Meteorological Society, Vol. 77, No. 7, 1507-1518.

Klinenberg, E, 2002. Heat Wave: A Social Autopsy of Disaster in Chicago. The University of Chicago Press. 320 p.

Illinois State Water Survey

2204 Griffith Dr
Champaign, IL 61820-7463
217-333-0729
jimangel@illinois.edu

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