This visualization implements the rooftop cooling transfer functions described by Guerin & Melkonian. Three intervention strategies reduce urban heat island intensity in Charlestown.
λ = latent heat of vaporization (~2450 kJ/kg), ET = evapotranspiration rate. Grass and small plants cool ~50-150 W/m²; mature tree canopy can reach ~150-400 W/m² at peak daytime.
Isolar ~ 800-1000 W/m² at peak. Every 0.1 increase in albedo reduces absorbed heat by ~80-100 W/m². White roof coatings are among the fastest, lowest-cost interventions.
Each liter of water evaporated per m² yields ~680 Wh of cooling. 1 liter over 8 hours provides ~85 W/m² average cooling.
| Strategy | Typical Cooling |
|---|---|
| Vegetation (grass/plants) | ~50-150 W/m² |
| Vegetation (trees/canopy) | ~150-400 W/m² |
| Albedo increase (Δα = 0.1) | ~80-100 W/m² |
| Evaporating 1 L/m² over 8h | ~85 W/m² |
Absorbance controls water retention ("sponginess"). Low absorbance = more water retained = more evaporative cooling (up to 85 W/m²).
Albedo controls surface reflectance. Higher values reflect more sunlight, reducing heat absorption by ~90 W/m² per 0.1 step.
Greenery controls vegetation coverage. Higher values increase evapotranspiration cooling up to ~300 W/m².
Stephen Guerin, Harvard Visualization Lab, Earth & Planetary Sciences
Alec Melkonian, Harvard Graduate School of Design