🧱 Urban Heat Island — City Temperature Map
Urban surfaces (asphalt, concrete, rooftops) absorb significantly more solar energy than vegetation or water. The resulting urban heat island (UHI) effect can raise city temperatures 5–12 °C above surrounding rural areas. Paint the city grid and watch the real-time temperature heatmap evolve.
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Physics
Each cell's temperature evolves according to: C·dT/dt = α·Qsun − k·(T − Tamb) − L·max(0, T − Tamb) + D·∇²T where α is solar absorptivity, k is convective loss, L is latent cooling (evapotranspiration for vegetation), and D·∇²T is thermal diffusion from neighbours. Vegetation (grass, trees) stays cool via evapotranspiration — the same mechanism that makes forests 5–10°C cooler than nearby city centres on a hot summer day.
Did you know?
The urban heat island effect was first documented by Luke Howard in 1818 for London. Modern cities like Phoenix (AZ) or Tokyo can be over 10°C hotter than surrounding rural areas at night. Green roofs, urban trees, and reflective "cool pavements" are among the most effective countermeasures.