The 1995 Chicago heat wave was a heat wave which led to approximately 750 heat-related deaths in Chicago over a period of five days.[1] Eric Klinenberg, author of the 2002 book Heat Wave: A Social Autopsy of Disaster in Chicago, has noted that in the United States, the loss of human life in hot spells in summer exceeds that caused by all other weather events combined, including lightning, rain, floods, hurricanes, and tornadoes.[2][3] The heat wave heavily impacted the wider Midwestern region, with additional deaths in both St. Louis, Missouri[4] and Milwaukee, Wisconsin,[5] as well.
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The temperatures soared to record highs in July with the hottest weather occurring from July 12 to July 16. The high of 106 °F (41 °C) on July 13 was the second warmest July temperature (warmest being 110 °F (43 °C) set on July 23, 1934) since records began at Chicago Midway International Airport in 1928. Nighttime low temperatures were unusually high; in the upper 70s and lower 80s °F (about 26 °C)—as well. Record humidity levels also accompanied the hot weather. The heat index reached 119 °F (48 °C) at O'Hare airport, and 125 °F (52 °C) at Midway Airport.
At the peak of the heat wave, as was the case in the summer of 1988, and possibly 1977, Madison, Wisconsin probably would have broken its all-time maximum temperature record of 107 °F (42 °C) had the reporting station been in the same location as it was during the 1930s.
The humidity made a large difference for the heat in this heat wave when compared to the majority of those of the 1930s, 1988, 1976–78 and 1954–56, which were powered by extremely hot, dry, bare soil and/or air masses which had originated in the desert South-West. Each of the above mentioned years' summers did indubitably have high-humidity heat waves as well, although 1988 was a possible exception in some areas. Moisture from previous rains and transpiration by plants drove up the humidity to record levels and the most humid air mass originated over Iowa previous to and during the early stages of the heat wave. Numerous stations in Iowa, Wisconsin, Illinois and elsewhere reported record dew point temperatures above 80 °F (27 °C) with a probable peak at 86 °F (30 °C) reported from at least one station in Wisconsin on 13 July 1995; this added to the heat to cause heat indices above 130 °F (54 °C) in Iowa and southern Wisconsin on several days of the heat wave as the sun bore down from a cloudless sky and evaporated even more water seven days in a row.
A more typical result of surface dew points above 80 °F (27 °C) are extreme precipitable water readings as well as other indices used to forecast severe thunderstorms and flooding such as Convective available potential energy as was illustrated in early June 2008 when thunderstorms originating in Minnesota and Iowa mushroomed when hitting the area of extreme dew points in South-Central and South-East Wisconsin from 77 to 84 °F (25 to 29 °C) and inaugurated the third wave of upper Middle West flooding (the first was snowmelt from the record-breaking winter snows and the third was the widespread rains in excess of 10 inches (250 mm) and up to 21 inches (530 mm) during early August 1997) by producing extremely heavy rain over the region, with many areas receiving 5 inches (130 mm) and a few areas of 10 to 15 inches (250 to 380 mm) in 3 to 6 hours' time.
A few days after, the heat moved to the east, with temperatures in Pittsburgh, Pennsylvania reaching 100 °F (38 °C) and in Danbury, Connecticut, 106 °F (41 °C) which is Connecticut's highest recorded temperature.
The dew points in question appear to be at or near national and continental records set a various times in the past; dew point records are not as widely kept as those of temperature and so on. Evidence points to the world record most likely being close to or in excess of 100 °F (38 °C) at locations along the Red Sea coast of Saudi Arabia.
Most of the heat wave victims were the elderly poor living in the heart of the city, who either had no working air conditioning or could not afford to turn it on. Many older citizens were also hesitant to open windows and doors at night for fear of crime.[6] Elderly women, who may have been more socially engaged, were less vulnerable than elderly men. By contrast, during the heat waves of the 1930s, many residents slept outside in the parks or along the shore of Lake Michigan.[2]
Because of the nature of the disaster, and the slow response of authorities to recognize it, no official "death toll" has been determined. However, figures show that 739 additional people died in that particular week above the usual weekly average.[7] Further epidemiologic analysis showed that blacks were more likely to die than whites, and that Hispanics had an unusually low death rate due to heat. At the time, many blacks lived in areas of sub-standard housing and less cohesive neighborhoods, while Hispanics at the time lived in places with higher population density, and more social cohesion.[2]
Mortality displacement refers to the deaths that occur during a heat wave that would have occurred anyway in a near future, but which were precipitated by the heat wave itself. In other words, people who are already very ill and close to death (expected to die, for instance, within days or a few weeks) might die sooner than they might have otherwise, because of the impact of the heat wave on their health. However, because their deaths have been hastened by the heat wave, in the months that follow the number of deaths becomes lower than average. This is also called a harvesting effect, in which part of the expected (future) mortality shifts forward a few weeks to the period of the heat wave. Initially some public officials suggested that the high death toll during the weeks of the heat wave was due to mortality displacement, an analysis of the data later found that mortality displacement during the heat wave was limited to about 26% of the estimated 692 excess deaths in the period between June 21 and August 10, 1995. Mortality risks affected Blacks disproportionally. Appropriately targeted interventions may have a tangible effect on life expectancy.[8]
Impacts in the Chicago urban center were exacerbated by an urban heat island that raised nocturnal temperatures by more than 2 °C (3.6 °F).[9] Urban heat islands are caused by the concentration of buildings and pavement in urban areas, which tend to absorb more heat in the day and radiate less heat at night into their immediate surroundings than comparable rural sites. Therefore, built-up areas get hotter and stay hotter.
Other aggravating factors were inadequate warnings, power failures, inadequate ambulance service and hospital facilities, and lack of preparation.[10] City officials did not release a heat emergency warning until 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.[2]
Another powerful factor in the heat wave was that a temperature inversion grew over the city, and air stagnated in this situation. Pollutants and humidity were confined to ground level, and the air was becalmed and devoid of wind. Without wind to stir the air, temperatures grew even hotter than could be expected with just an urban heat island, and without wind there was truly no relief. Without any way to relieve the heat, even the inside of homes became ovens, with indoor temperature exceeding 90 °F (32 °C) at night. This was especially noticeable in areas which experienced frequent power outages. At Northwestern University just north of Chicago, summer school students lived in dormitories without air conditioning. In order to ease the effects of the heat, some of the students slept at night with water-soaked towels as blankets.
The scale of the human tragedy sparked denial in some quarters, grief and blame elsewhere.[2] From the moment the local medical examiner began to report heat-related mortality figures, political leaders, journalists, and in turn the Chicago public have actively denied the disaster's significance. Although so many city residents died that the coroner had to call in nine refrigerated trucks to store the bodies, skepticism about the trauma continues today. In Chicago, people still debate whether the medical examiner exaggerated the numbers and wonder if the crisis was a "media event."[3] The American Journal of Public Health established that the medical examiner's numbers actually undercounted the mortality by about 250 since hundreds of bodies were buried before they could be autopsied.[7]
Chicago's daily low and high in 1995:
During the week of the heat wave, there were 11% more hospital admissions than average for comparison weeks and 35% more than expected among patients aged 65 years and older. The majority of this excess (59%) were treatments for dehydration, heat stroke, and heat exhaustion.[11]