Urban Heat Island Calculator
An estimate of the urban heat island effect from a neighbourhood's hard surface, tree canopy and surface reflectance — and how much cooling more canopy or lighter surfaces would buy.
Hard, dark surfaces absorb heat by day and release it at night; canopy shades and evaporates; light surfaces reflect.
How the urban heat island calculator works
Hard, dark surfaces absorb heat by day and release it at night; canopy shades and evaporates; light surfaces reflect. The estimate here is a simple linear model fitted to the published relationships — roughly 0.06 °C per percentage point of impervious surface, offset by canopy and albedo.
It is an estimate for comparing options, not a measurement. Its value is in the deltas: what 10% more canopy does is far more reliable than the absolute number.
Formula: ΔT ≈ 0.06 × impervious% − 0.04 × canopy% − 8 × (albedo − 0.2)
Worked examples
| Inputs | Estimated heat island intensity (°C) | Note |
|---|---|---|
| A typical suburb | 3.46 | about 3.5 °C |
| A leafy suburb | 1.46 | about 1.5 °C |
| An industrial area | 5.92 | severe |
FAQFrequently asked questions
What is the urban heat island effect?
Cities running warmer than their surroundings, especially at night, because hard surfaces store the day's heat and there is less evaporation to shed it.
How big is it?
Two to five degrees on a summer night in most cities; up to ten in extreme cases. It is the difference between a warm night and a dangerous one.
What cools a neighbourhood fastest?
Tree canopy, by a wide margin — shade plus evapotranspiration. Light-coloured roofs and pavements are the next lever, and the cheapest.
How reliable is this estimate?
The differences between options are reasonably robust; the absolute number is not. Use it to compare designs, not to predict a temperature.
What is albedo?
The share of sunlight a surface reflects. Fresh asphalt is about 0.05, concrete 0.3, a white roof 0.7 or more.
Where these figures come from
- UN-Habitat — Urban Indicators Guidelines — density, green space and public space benchmarks
- World Health Organization — Urban green spaces — the 9 m² per person minimum
- ITE — Parking Generation Manual — parking demand rates by land use
- Office for National Statistics — Population estimates — the UK's national statistics agency
Last checked: September 2026. Default per-capita rates are mid-range figures from national statistical agencies and utility reports; every one is an input you should replace with the local figure.