Air Temperature

Using i-Tree Cool Air, the hottest day across the study area was simulated at a 300m raster resolution. These runs were combined to create a map representing the hottest air temperature reached throughout the area.

Attribute	Degrees (°F)
Average Maximum Temperature	92.8
90th Percentile Maximum Temperature	100.0

Heat Index

The average maximum heat index in 2021 is represented at the census block group level.

Attribute	Degrees (°F)
Average Maximum Heat Index	96.1
90th Percentile Maximum Heat Index	109.3

Heat Index is defined as the apparent temperature in shaded areas based on the air temperature and relative humidity. Thresholds of heat index safety set by the National Weather Service (NWS) are as follows:

Heat Index	Classification	Effect on the body with prolonged exposure/activity
80-90°F	Caution	Fatigue possible
90-103°F	Extreme Caution	Heat stroke, heat cramps, or heat exhaustion possible
103-124°F	Danger	Heat cramps or heat exhaustion likely, and heat stroke possible
125°F+	Extreme Danger	Heat stroke highly likely

Normalized Risk Scale

The normalized risk scale is between 0 and 1, based on the following formula:

Risk = place value of air temperature / value of maximum US region value

Effects of Canopy on Extreme Heat

Canopy cover was adjusted for i-Tree Cool Air simulations to compare the Heat Index at -50% canopy cover to +50% canopy cover.

Attribute	Temperature (°F)
-50% Canopy	95.1
+50% Canopy	91.4
Average temperature increase per 10% loss of canopy1	+0.46
Average temperature decrease per 10% gain of canopy1	-0.28

¹Where each pixel is a surface area of 90000m², 1% is equal to 900m² of canopy. For more information, see the Methodology section.

Select from a slider or GIF below to view how canopy cover affects temperature:

Effects of Impervious Cover on Extreme Heat

Impervious cover was adjusted for i-Tree Cool Air simulations to compare the Heat Index at -50% impervious cover to +50% impervious cover.

Attribute	Temperature (°F)
+50% Impervious Cover	95.7
Average temperature increase per 10% gain of impervious cover1	+0.58

¹Where each pixel is a surface area of 90000m², 1% is equal to 900m² of impervious area. For more information, see the Methodology section.

Select from a slider or GIF below to view how impervious cover affects temperature:

Heat in Urban Areas

Census block groups within urban areas as defined by the United States census were isolated for a separate analysis. For a more in-depth look at urban heat, see the maps on the next tab.

Land Planning Impacts on Temperature in Boston

A Census-designated Urban Area was chosen for each subregion as an example of finer-resolution analyses that can be done with i-Tree Cool Air outputs.

Select canopy or impervious cover below to view its impacts on the urban center: