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Research Findings: Objective 3

Apply the Model to the City of Montreal to Identify Census Tracts with the Least Tree-Cover and Greatest Heat Vulnerability

Results from the three model segments are outlined below.

(1) Canopy Cover

The model isolates trees from the LiDAR point cloud and develops a shapefile of canopy coverage for the City of Montreal (Figure 5). This shape-file is then aggregated to the census tract and the 25% of tracts with the lowest tree canopy coverage are identified (Figure 6). Canopy cover among the tracts with lowest coverage ranges from 4.6 to 14.3%.  Canopy cover in all populated tracts ranges from 4.6 to 58.0%. 

A map of the Island of Montreal which shows tree canopy cover which was derived from LiDAR data. The canopy is highly variable across the island. There is a large patch of treeless area near the centre of the island, indicating the location of Pierre Elliot Trudeau Airport. There are large clustering of trees around Mount Royal as well as on the western portion of the island near Kirkland.

Figure 5. Tree canopy cover for the Island of Montreal derived from LiDAR data.

Map of Census Tracts Identified as High Priority for the Canopy Cover Variable. Highlighted tracts have minimal tree-cover ranging from 4.6 to 12.9 per cent coverage. Notable neighbourhoods containing a large number of high vulnerability tracts are La Salle to the centre-south, Ville Marie to the centre-east, and the centre-north neighbourhood of Montreal-Nord.

Figure 6. Map of Census Tracts Identified as High Priority for the Canopy Cover Variable.

 

(2) Socioeconomic Variables

Each tract is indexed based on percent prevalence of variables 1-7, and the 25% most vulnerable census tracts are identified for each socioeconomic variable. Figures 7-13 show high- and low-vulnerability tracts within the City of Montreal based on each socioeconomic variable: Age (Figure 7), Income (Figure 8), Education (Figure 9), Ethnicity (Figure 10), Social Isolation (Figure 11), Height of Housing Structure (Figure 12), and Age of Housing structure (Figure 13). In each figure the high priority tracts are identified in pink, and low priority tracts are shown in grey.

(3) Proximity to cooling centers

Average proximity to cooling infrastructure is derived for each census tract. Figure 14 shows the top 25% most vulnerable census tracts based on proximity to cooling infrastructure; residents of these tracts have the greatest average Euclidean distance to travel to access their nearest cooling center. 
 

Final Model Output

A bivariate heat vulnerability map shows the distribution of combined vulnerability throughout Montreal based on the indexed multi-variable vulnerability scores (Figure 15). Those tracts with greatest social heat-vulnerability and lowest tree cover make up the highest-priority tracts. 

Bivariate map of the Island of Montreal showing the census tracts falling into 9 categories ranging over 2 criterion, Tree Canopy Coverage and Socioeconomic Vulnerability. Groupings of low vulnerability, high canopy cover neighbourhoods are towards the southwest and centre of the city. Highly vulnerably and low canopy cover tracts are concentrated toward the centre-east and northern portion of the island.

Figure 15. Bivariate heat map of the Island of Montreal. Tracts are ranked on a spectrum of both Canopy Cover and Socioecnomic Vulnerability. Tracts with High Vulnerability and Poor Cover (highest priority) are designated dark green while tracts with Low Vulnerability and Good Canopy coverage are denoted in light green.

The choropleth resulting from Equation 1 is used to conduct the Hot Spot Getis-Ord Gi* analysis. This analysis identifies areas of greatest vulnerability (hot spots) and least (cold spots) vulnerability to heat. The model identifies three areas of high vulnerability with a 99% confidence level as shown in Figure 16. These areas are extracted from the map and overlaid onto the bivariate heat map of tree cover and socioeconomic vulnerability to find the most vulnerable tracts in Montreal. Figure 17 shows the 10 high-priority tracts located within two of the three high-priority areas. These ten tracts are highly vulnerable to heat and have minimal canopy cover. These are the tracts that require increased canopy cover and should be the focus of future tree planting efforts in Montreal. 

A map of the Island of Montreal showing the areas of highest and lowest heat vulnerability. Three areas were shown to be highly vulnerable with ninety nine percent confidence. These neighbourhoods are Ville-Marie, Montreal-Nord/Saint Leonard, and LaSalle.

Figure 16. Heat map of census tracts in Montreal that represent areas of highest and lowest heat vulnerability. The three areas that are highly vulnerable with 99% confidence are Ville-Marie (centre-right), Montreal-Nord/Saint Leonard (top), and LaSalle (bottom).

A map of Montreal indicating the ten most vulnerable census tracts. The majority of the tracts lie near the right edge of the Island in the neighbourhood of Ville-Marie. Two of the tracts are located in the Montreal Nord/Saint Leonard area in the North of the island.

Figure 17. Map of the ten most heat vulnerable census tracts in Montreal. The model has determined that these tracts would benefit the most from increased tree planting to mitigate heat vulnerability.

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