Identify Factors Related to Heat Vulnerability and Tree Canopy Heat Mitigation
Seven socioeconomic variables and two biophysical variables influencing residential heat vulnerability are described below.
Variable 1: Age
People over the age of 65 make up one of the communities most vulnerable to extreme heat (Hansen et al., 2011). Mortality of residents over the age of 65 increased during extreme heat events in Ontario cities (Smoyer et al., 2002). Elderly people are at especially high risk of heat-related illness during heat waves due to their reduced physiological capacity to regulate body temperature (Stewart et al., 2017). In addition to physiological vulnerability, Hansen et al. (2011) found that ownership and working knowledge of air conditioners were among barriers to heat adaptability among older adults. Heat events also present heightened risk to children under the age of 4; sudden infant death increases during extreme heat events (Ho, Knudby and Huang, 2015; Auger, et al., 2015).
Variable 2: Income
Low income earning is associated with increased urban heat-related mortality (Reid, 2009). People earning low incomes typically have fewer resources with which to mitigate personal heat exposure; for example, low-income residents often have insufficient money to purchase and operate home air conditioning (Ho, Knudby and Huang, 2015). Lack of air-conditioning limits low-income residents’ capacity to manage their own body temperatures, making them more susceptible to heat related illness (O’Neill, Zanobetti and Schwartz, 2005).
Variable 3: Education
Limited education associates with higher risk of heat-related illness (Ho, Knudby and Huang, 2015; Reid, 2009). This is partially attributed to the association between limited education and employment in physically demanding and often outdoor labour, which exposes workers to extreme heat during the day (O’Neill et al., 2005). Further, neighbourhoods with lower average education levels are more likely to be situated in heat-retaining urban microclimates and are more vulnerable to extreme heat (Harlan et al., 2006). The inclusion of limited education as a factor of urban residential heat vulnerability follows practice outlined in similar heat vulnerability studies (Reid et al., 2005; Harlan et al., 2006; Ho, Knudby and Huang 2015).
Variable 4: Ethnicity
Racial minorities face a heightened risk of heat-related illness (O’Neill et al., 2005). A number of phenomena explain this association. In North American cities, non-white populations associate spatially with lower residential tree-cover and greater heat-retaining neighbourhood surfaces (e.g. asphalt), thus experiencing increased heat vulnerability (Jesdale et al., 2013). Additionally, household air conditioner use (a significant heat-mitigating practice) is more prevalent among white urban residents than among other racial groups (O’Neill et al., 2005; Reid et al., 2005).
Variable 5: Social Isolation
Individuals who live alone have increased vulnerability to extreme heat events and experience higher levels of heat-related mortality than do residents with daily social contact (Ho, Knudby and Huang, 2015; Reid et al., 2009). Many heat-related deaths occur when urban residents are alone (Klinenberg, 2003) and occur at higher rates among residents who do not leave the house each day (Reid et al., 2005; Stewart, 2017).
Variable 6: Height of housing structure
High-rise apartment buildings retain more heat than fewer-story buildings (Smoyer-Tomic et al., 2002; Chan et al., 2007). Residents living within high-rise buildings are at an elevated risk of heat-related illness and mortality, and during extreme heat events residents are more likely to be exposed to higher average indoor temperatures (Xu et al., 2013; Buscail et al., 2012).
Variable 7: Age of housing structure
Similarly to high-rise apartments, old residences retain more heat than newer buildings as they have less capacity to dissipate absorbed heat (Smoyer-Tomic et al., 2002; Xu et al., 2013). During extreme heat events, residents of apartment buildings constructed prior to 1970 are more likely to be exposed to higher average indoor temperatures (Buscail et al., 2012; Ho et al., 2015). In addition to high at-home temperatures, Xu et al. (2013) found heat-related mortality increased in census tracts with a high proportion of old buildings.
Variable 8: Proximity to public cooling infrastructure
Publicly accessible air-conditioned buildings, indoor and outdoor pools, and splash pads all become critical resources for residents in a heat wave (Stewart, 2017). Proximity to these public cooling centers improves residents’ capacity to manage their own body temperatures, and especially reduces the heat vulnerability of socioeconomically disadvantaged residents (Fraser, Chester and Eisenman, 2017). The City of Montreal provides such cooling centers for the entire summer, with improved access and extended hours during heat events (Ville de Montréal, 2018).
Variable 9: Canopy Cover
Tree coverage in urban spaces is known to provide a cooling effect due to the shade that they provide in otherwise bare and hot landscapes (Leuzinger et. al, 2010; Shashua-Bara and Hoffmanab, 2000; Akabari and Taha, 1992). Where there are high temperatures, higher shade areas are required for providing residents with relief and impacting microclimates (Rahman et. al, 2017; Leuzinger et. al, 2010). In this analysis, canopy cover is used to show the total amount of shade; more canopy cover results in greater areas of shade.