The Role of Maps in Neighborhood-Level Heat Vulnerability Assessment for the City of Toronto

Article excerpt


Hot weather can have a serious impact on human health. Researchers have studied the effects of extreme heat events on the human body and found a spectrum of impacts ranging from heat rash and sun burn to more complicated illnesses such as heat cramps, fainting, and heat exhaustion (Smoyer-Tomic and Rainham 2001 ; Basu and Samet 2002; Smoyer-Tomic et al. 2003; Ebi 2007; Pengelly et al. 2007). Heat stroke is the most severe illness related to heat and occurs when the body's core temperature reaches 41[degrees]C or more (Ebi 2007). This usually only occurs when heat exhaustion is not noticed or treated, and it is accompanied by hot, dry skin, fast pulse, headache, or coma. Heat stroke can result in complications including kidney, liver, and brain damage and ultimately death (Barrow and Clark 1998; Bouchama and Knochel 2002). According to statistics available from the U.S. National Weather Service, over the past ten years, heat accounted for almost half of all deaths and injuries attributed to atmospheric phenomena in the country--more than any other weather-related cause (NWS 2008).

The health effects vary depending upon the length and severity of the heat wave as well as the body's ability to dissipate extra heat. A number of studies have shown that heat-related mortality significantly increases during prolonged hot and oppressive weather conditions (Kalkstein and Greene 1997; Kilbourne 1997); this impact is exacerbated with the additional effect of air pollution (Cheng et al. 2007). Further, morbidity as indicated by emergency calls and emergency department visits has also been shown to increase during periods of high daily temperatures (Semenza et al. 1999; Dolney and Sheridan 2006; Bassil et al. 2007). Populations in temperate regions tend to be at an increased risk for heat stress in comparison with warmer regions, in large part due to the greater seasonal fluctuation in temperatures and the lack of acclimatization to increasing temperatures (Kalkstein and Davis 1989; Basu and Samet 2002). The health impacts of insufficient acclimatization have been demonstrated in studies which suggest that heat waves earlier in the season result in more deaths than those occurring later in the summer (Kalkstein and Davis 1989).

Environment Canada predicts that the number of days with temperatures over 30 degrees in Toronto will more than triple from about 15 days per year between 1961-1990 to about 65 days per year by 2080-2100. A historical analysis of heat-related mortality for the period 1953 to 2000 estimated that on average, 120 people die prematurely each year in Toronto due to summer heat, with large variations from year to year depending on weather conditions (Pengelly et al. 2007). Many studies indicate that urban areas such as Toronto are at increased risk for health effects from increased heat. The urban environment poses a particular risk for heat episodes, given the presence of the "urban heat island" where temperatures can range up to 11[degrees]C warmer than surrounding regions due to limited vegetative cover and large expanses of asphalt (Aniello et al. 1995).

The City of Toronto has a heat health alert system in place which guides the Medical Officer of Health in calling heat alerts when the weather conditions pose an increased risk to health (Toronto Public Health 2009a). In response to an alert, Toronto's hot weather response plan is activated by Toronto Public Health, which initiates a number of interventions including mass media broadcast messaging, opening cooling centers, and providing outreach through social services. Over the summer of 2007 there were 10 days with a heat alert and five clays with an extreme heat alert (Toronto Public Health 2009a). Over the summer of 2008, there were three days with a heat alert and six days with an extreme heat alert (Toronto Public Health 2009a).

In addition to the general physiological risk of heat-related illness there are intrinsic and extrinsic factors that can increase this risk for individual persons and for population groups, making them particularly vulnerable. …