Heat Wave Scorches Chicago

A young Chicagoan cools off as temperatures reached close to 100°F on July 3rd, 2012. Source: https://www.cbsnews.com/news/chicago-melts-in-heat-wave-of-triple-digit-temps/

Between July 4 and July 7, 2012, a nationwide heat wave descended upon Chicago, IL, hitting the city with the highest temperatures in almost 20 years. Chicago reached 100°F for three consecutive days, with a high of 103°F on July 5th and 6th recorded at Chicago O’Hare International Airport. Despite not being dramatic events or particularly destructive towards infrastructure, heatwaves account for the most deaths related to a natural hazard, often proving deadly to the old, the very young, the ill, and the poor. This heatwave took six lives.

In late June 2012, The heat wave formed when a dome of high pressure air center above the Baja California Peninsula and strengthened dramatically, then began to move northeastward. Underneath this high pressure, the air sinks toward the surface, which then acts as a dome capping the atmosphere. The cap traps heat and prevents it from rising. Without the lift, there is little or no convection, and thus no convective clouds form. The lack of convective clouds means small chances for rain. The final result of this is a build-up of heat at the surface.

Formation of a Heat Wave, as high pressure traps heat near the ground. Source: U. S. National Weather Service - https://www.weather.gov/jetstream/hi

An factor that tends to aggravate heat waves is Chicago’s ‘urban heat island’, which tends to raises the nocturnal temperatures by more than 4 degrees. These heat islands are caused by the concentration of buildings and pavement in urban areas, which absorb more heat in the day, ultimately making the area get hotter, as well as stay hotter.

The 103°F temperatures occurring were the highest temperatures observed since July 13th, 1995, when over 104°F was observed during a heatwave that led to 739 deaths over a period of 5 days in the Chicagoland area. The warmest consecutive days of each of these heat waves were virtually the same, temperature-wise. A key difference is the humidity factor, as the Temperature Humidity Index was considerably higher in 1995. Additionally, the 1995 heat wave daytime heat indices average (the combination of temperature and relative humidity) was much more intense, as the heat index reached 114.2°F on Day 2 of the event. When heat indices get over 105°F, the ability of the body to keep its internal temperature regulated decreases dramatically.

Charts indicating the high intensity of the 1995 heatwave,
 and additionally showing the high temperatures of the 2012 heat wave.
Source: https://www.wunderground.com/blog/weatherhistorian/why-was-the-chicago-heat-wave-of-2012-so-much-less-deadly-than-that-of.html

One thing that additionally improved Chicago’s response to the heat wave was the local emergency response to extreme weather events. The heat watch, warning, and advisory system has improved since 1995, as in 1995, a heat emergency was only issued city-wide on the last day of the event. Additionally, since 1995, the Chicago Office of Emergency Management and Communications has consolidated emergency responders, the 311 Call Center, Traffic Management Authority and a public infrastructure center all under one roof. This allows for better mobilization of emergency response. During a heatwave, the National weather service advises minimum time outside, wearing loose fitting clothing, drinking plenty of water, and scheduling rest breaks for oneself.

However, much of Chicago is still in danger in the event of a high intensity heat wave. During a heat wave, residents of areas with high crime rates tend to avoid sleeping outside and will not open their windows, a reminder that those most impacted by hazards such as heat waves are often inhibited by factors beyond their control.

Works Cited:

Burt, Christopher C. “Why Was the Chicago Heat Wave of 2012 so Much Less Deadly than That of 1995?” Weather Underground, 27 July 2012, 6:22 PM, www.wunderground.com/blog/weatherhistorian/why-was-the-chicago-heat-wave-of-2012-so-much-less-deadly-than-that-of.html.

Burt, Christopher C. “The Amazing June Heatwave of 2012. Part 1: The West and Plains June 23-27” Weather Underground, 29 June 2012, 8:17 PM, https://www.wunderground.com/blog/weatherhistorian/the-amazing-june-heat-wave-of-2012-part-1-the-west-and-plains-june-2.html. 

Hyndman, David and Donald Hyndman. Natural Hazards and Disasters. 5th ed., Cengage Learning, 2017.

Rubin, Bonnie Miller, and Jeremy Gorner. “Fatal Heat Wave 20 Years Ago Changed Chicago's Emergency Response.” Chicagotribune.com, Chicago Tribune , 21 July 2016, 6:51 AM, www.chicagotribune.com/news/ct-chicago-heat-wave-20-years-later-met-20150715-story.html.

US Department of Commerce, and NOAA. “July 4-7, 2012 Heat Wave.” National Weather Service, NOAA's National Weather Service, 17 June 2015, www.weather.gov/lot/2012July_heat.