GLOSSARY
Urban Heat Island
The urban heat island effect makes cities measurably hotter than surrounding countryside: concrete, asphalt and rooftops absorb solar radiation all day and re-radiate it, keeping urban air warmer — especially through evenings.
Also known as: Heat island effect · UHI
What the urban heat island is
Cities replace vegetation with hard, dark, dense materials. Concrete and asphalt absorb solar radiation through the day and release it slowly, waste heat from vehicles and air conditioners adds to the load, and street canyons trap it all. The result is measurable: urban districts run warmer than the countryside around them, with the gap most pronounced in the evening as stored heat radiates back out.
Why it matters for public space
The heat island empties squares, parks and walkways at exactly the hours they should be most alive. Long-term, the correction is greening — tree canopy shades and transpires. Short-term, and on hard plazas that can’t be planted, evaporative approaches fill the gap.
Where misting fits
Mist zones at gathering points, walkways and transit stops cool the spots people actually occupy without wetting them — the physics here, and the full public-space approach, including the honest trees-first hierarchy, in public space cooling.