Extreme heat events are responsible for more deaths in the United States than floods, hurricanes and tornados combined according to NOAA. Yet, highly publicized events, such as the 2003 heat wave in Europe which caused in excess of 35,000 deaths, and the Chicago heat wave of 1995 that produced 465 deaths, draw attention away from the countless thousands who, each year, fall victim to health emergencies and illnesses directly attributed to heat. The health impact of heat waves and excessive heat are well known. Cities world wide are seeking to better understand heat related illnesses in respect to the specifics of climate, social demographics and spatial distributions. This information can support better preparation for heat related emergency situations with regards to planning and placement of emergency resources and personnel.

This study deals specifically with the relationship between climate and heat related emergency (911) calls in Chicago, Illinois between 2003 and 2006. It is part of a larger, more complex study, that includes urban morphology and social factors that impact heat related emergency dispatch calls (HRD) in Chicago. This particular study examines the seasonality, local climate conditions, and other factors that impact HRD, particularly days with high HRD. Simple explanations for higher HRD, such as day of week, maximum temperature, or heat index are not readily evident. This study examines trends in both annual and composite HRD data sets and presents some of the patterns and complexities associated with the increases in heat related emergency dispatches, primarily in relation to the local climate conditions.