The relationship between extreme heat and ambulance response calls for the city of Toronto, Ontario, Canada.

Concern over the impact of extreme heat upon human health has increased in recent years. Though much research has evaluated the relationships between the two, few studies have attempted to quantify this vulnerability on a sub-metropolitan area level. Using a Geographic Information System (GIS), ambulance calls for a 4-year period from 1999 to 2002 was analyzed in relation to extreme heat for the city of Toronto, Ontario, Canada. Ambulance response calls were plotted on a map to understand the spatial variability of where calls significantly increase above normal levels during oppressively hot days. Census data were used to identify the demographic characteristics of the population within these areas. Statistical tests were also used to assess the degree of correlation among different meteorological variables and the ambulance call data. Over the 4-year period, the average number of ambulance calls increases by 10 percent over normal levels on those days considered oppressively hot. A change in the spatial pattern of calls also occurs on such days. The urban core, with the greatest density of calls, experiences the greatest absolute percentage increase in calls from normal on oppressive days. However, it is some areas of the city located along the shore of Lake Ontario, where a high majority of the population goes to cool down, that demonstrate the greatest percentage increase in calls. Other areas of the city exhibiting an increase in calls are located within industrial and recreational areas.