The relationship between neighbourhood tree canopy cover and heat-related ambulance calls during extreme heat events in Toronto, Canada

Abstract

The relationship between neighbourhood tree canopy cover and heat-related ambulance calls during extreme heat events in Toronto, Canada Two thirds of Canadians reside in urban areas and 85% of recent population growth occurs in these areas. The intensity and duration of extreme hot weather events are predicted to increase in Canadian cities and in cities globally. It is well established that human suffering due to extreme heat is exacerbated in urban as compared to rural environments. Understanding the characteristics of urban landscapes that play the greatest roles in exacerbating the human health impact of extreme heat is thus imperative. This study explores the relationship between the amount of canopy cover from trees and the incidence of heat-related morbidity during extreme heat events in 544 neighbourhoods of Toronto, Ontario, Canada. Four extreme heat events from three years were studied. Heat-related ambulance calls were found to be 12.3% higher during the heat events than in the preceding or the following week. The number of heat-related ambulance calls was negatively correlated to canopy cover (Spearman Rank rho = −0.094, p = 0.029) and positively correlated to hard surface cover (Spearman Rank rho = 0.150, p < 0.001). Toronto neighbourhoods, as defined by Census Tracts, with less than 5% canopy cover had approximately five times as many heat-related calls as those with greater than 5% tree canopy cover, and nearly fifteen times as many heat-related calls as Census Tracts with greater than 70% tree canopy cover. These data suggest that even a marginal increase in the tree canopy cover from <5% to >5% could reduce heat-related ambulance calls by approximately 80%. These results have important implications for human health during heat events, particularly in the context of global climate change and urban heat islands, both of which are trending toward hotter urban environments in future.

Effects of physical activity and shade on the heat balance and thermal perceptions of children in a playground microclimate

“…Human thermal comfort (TC) assessed through heat balance modeling and/or subjective surveys varies across age, sex, activity level, and location, yet few models have examined TC in children and youth during physical activity in outdoor spaces. Outdoor TC is also an essential parameter to assess the value of an outdoor recreational space based on intended use and health benefits (e.g., activity types) [1,2], to improve urban well-being using urban microclimatic design [3], and to guide sustainable urban development [4]. The majority of TC models are based on indoor studies and stem from TC perceptions and physiological parameters of adult subjects [5e7], with little-to-no certainty that the models can be applied to children [8].…”

Evidence-Based Landscape Architecture for Human Health and Well-Being

“…What is less well-known is the variation in distribution of heat-related illnesses across a city and whether the characteristics of a neighborhood has an effect. Graham et al [21] investigated the relationship between physical characteristics of urban areas and the number of emergency medical services (EMS) calls during heat waves in Toronto, Canada. Their results showed that areas with lower tree canopy cover proportions and a higher percentage of hard surfaces corresponded to higher numbers of EMS calls-up to five times higher for areas with very low amount (under 5%) of canopy cover.…”

Outdoor Thermal Comfort during Anomalous Heat at the 2015 Pan American Games in Toronto, Canada

“…and shade are routinely associated with reductions in summertime temperatures and improvements in thermal comfort (TC) [10,11]. Studies performed in Toronto demonstrate 'urban cool islands' [12], as well as associations between canopy cover and emergency response calls [13].…”

“…The COMFA human EB model is a mathematical model designed to estimate the TC of an individual at a given place and time. Studies have both tested and incorporated revisions into the model to ensure agreement between predicted TC estimates and actual TC responses during both sedentary and non-sedentary activity [13,[48][49][50]. The model requires meteorological inputs (T a , absorbed radiation (R abs ), RH, and V w ) and personal inputs (metabolic activity, M act , and activity velocity, V a ) to produce a human EB in Wm −2 , based on the following summation:…”

“…Spatial maps are helpful to guide urban planners looking to limit the highest heat levels in a city, and also help First Aid and emergency responders in determining high-risk locations for heat stress [12,13,72]. Any newly planned large-scale sporting events in the GTA can also make use of this new information for organization purposes, especially given that the mesonet station locations were situated at or near venues.…”