Evaluating Urban Canopy's Role in Alleviating Extreme Heat: An i-Tree Cool Air Analysis

West South Central Subregion

The West South Central subregion comprises Arkansas, Louisiana, Oklahoma and Texas. The urban area analyzed is the Houston Urban Area. The following are the maximum weather station recordings and locations for 2021:


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 96.2
90th Percentile Maximum Temperature 100.5

Heat Index

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

Attribute Degrees (°F)
Average Maximum Heat Index 98.7
90th Percentile Maximum Heat Index 106.5

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 98.2
+50% Canopy 94.4
Average temperature increase per 10% loss of canopy1 +0.4
Average temperature decrease per 10% gain of canopy1 -0.36

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:


canopy

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 101.0
Average temperature increase per 10% gain of impervious cover1 +0.96

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:


impervious

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.

Attribute Value Difference from National Urban Average
Average Temperature (°F) 96.8 +3.15
Average Heat Index(°F) 99.6 +4.46
Average temperature increase per 10% gain of impervious cover(°F) +1.0 -0.15
Average temperature increase per 10% loss of canopy(°F) +0.44 -0.19
Average temperature decrease per 10% gain of canopy(°F) -0.36 -0.04
90th percentile of temperature(°F) 100.8 -5.84
Average canopy cover for +90th percentile of temperature (%) 1.1 -1.94

Land Planning Impacts on Temperature in Houston

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:


canopy
canopy

Heat in Houston

Attribute Value Difference from Regional Values
Average Temperature (°F) 96.8 +0.6
Average Heat Index(°F) 105.4 +6.7
Average temperature increase per 10% gain of impervious cover(°F) +0.48 -0.52
Average temperature increase per 10% loss of canopy(°F) +0.04 -0.4
Average temperature decrease per 10% gain of canopy(°F) -0.26 +0.1
90th percentile of temperature(°F) 98.8 -2.0
Average canopy cover for +90th percentile of temperature (%) 0.9 -0.2