Ground surfaces and trees decide how hot a street feels. Asphalt stores the sun and sends the heat back to people. Depaving removes that heat source at once. Trees block the sun, but need years to grow. This example study puts numbers on both, for one real site, and compares four design options side by side.
This is an example study. It shows the method and how to compare options. It is not a design.
The question
Downtown Memphis has large asphalt parking lots and little shade. The city wants cooler streets for people who walk. Which change gives the most cooling for the money: more trees, depaved lots, or both? And where should the trees go?
Four design options
All four options change only trees and ground. Buildings and weather stay the same in every run.
| Option | Trees added | Acres depaved |
|---|---|---|
| Trees only | 62 | 0 |
| Depave + 60 trees, busiest places | 60 | 5.9 |
| Depave + 120 trees | 120 | 5.9 |
| Depave + 60 trees, coolest spots | 60 | 5.9 |
What we simulate: felt temperature
Felt temperature (UTCI, the Universal Thermal Climate Index) is how hot it feels to a person who walks outdoors. A model of the human body takes in air temperature, humidity, wind and radiation. Under a tree, the air temperature changes very little, but the felt temperature changes a lot. That is why we simulate felt temperature, not air temperature.
Infrared Core computes the felt temperature for every 3 ft × 3 ft cell at head height, over 83 acres (1,410 × 2,575 ft). Inputs: 3D buildings and trees from USGS lidar (2017), ground surfaces from land cover and OpenStreetMap, and a typical-year weather file for Memphis International Airport. Method: UTCI after Bröde et al. (2012).
We look at two time windows:
- Hottest July afternoon: 3 pm on a typical hottest July day, air temperature 96 °F.
- Summer daytime: June to August, 9 am to 6 pm, 920 hours. We count the hours that feel too hot: felt temperature above 79 °F, the start of moderate heat stress.
Result 1: the hottest afternoon
Today, a typical spot on the lots feels like 110 °F at 3 pm. Trees alone change the typical spot on the lots very little (−0.1 °F); under the new trees it is 1.2 °F cooler. Depaving the lots and planting 60 trees cools the lots by about 2 °F. With 120 trees, the lots cool by 2.5 °F.
Result 2: the whole summer
On the lots, 879 of 920 summer daytime hours feel too hot today. Depaving with 120 trees removes 13 of those hours, depaving with 60 trees removes 7. A single hot afternoon and a whole summer tell different stories: the peak changes more than the count of hot hours.
Key figures
Change against today, same weather.
| Option | Felt temp. at 3 pm, lots | Felt temp. at 3 pm, under new trees | Hours too hot, lots | Hours too hot, walkways | Cost ($M, ±50 %) | Time to effect |
|---|---|---|---|---|---|---|
| Trees only (62) | −0.1 °F | −1.2 °F | 0 h | −5 h | 0.18 | 15 to 30 years |
| Depave + 60 trees, busiest places | −1.9 °F | −2.4 °F | −7 h | −5 h | 2.7 | now / 15 to 30 years |
| Depave + 120 trees | −2.5 °F | −2.8 °F | −13 h | −5 h | 2.7 | now / 15 to 30 years |
| Depave + 60 trees, coolest spots | −2.0 °F | −2.8 °F | −7 h | −4 h | 2.6 | now / 15 to 30 years |
Walkways are footways and crossings within 430 ft of the changes. Depaving acts at once; trees need 15 to 30 years to give full shade (USDA Forest Service). New trees are modelled at full size: 33 ft high with a 26 ft crown.
What the study shows
- Depaving gives cooling from day one, and it is most of the cost.
- Trees give the strongest cooling per square foot, in their own shade.
- Placement matters more than count: trees placed where people walk keep most of the walkway benefit with half the trees.
Costs are national benchmarks with a range of ±50 %, not Memphis prices: $1,000 per tree in a lot (3 years of care), $6,000 per tree on Main Street Mall (soil cells), $9 per sq ft for depaving, soil and planting, $6 per sq ft for a light-concrete plaza. Design fees, utility relocation, irrigation, care after year 3, lost parking revenue and land are not included.
Run a study like this
Each option is one run of the thermal comfort models on the same 3D scene: change the trees and the ground materials, keep the buildings and the weather, and compare. Read how the engine computes felt temperature in Advanced thermal comfort and Simulation Engine Basics. To run your own options, start with the API and SDK.