Street Canyon Sky View Factor

Canyon Geometry

Building height H 18 m

Street width W 14 m

Building albedo (reflectivity) 20%

Simulation speed 1×

Live Readout

Time of day06:00

Sky view factor Ψ

1.00

Aspect ratio H/W

1.29

Canyon air temp

18.0 °C

Rural (open) temp

18.0 °C

Urban heat island intensity ΔT

0.0 °C

How it works

A street canyon's sky view factor Ψ is the fraction of the overhead hemisphere still visible from street level once the flanking buildings block part of the sky. For an (idealised, infinitely long) canyon of height H and width W, with aspect ratio a = H/W:

Ψ = √(1 + a²) − a        (a = H/W, at the canyon midline)

Ψ → 1 for an open field (a → 0) and Ψ → 0 for a deep, narrow canyon. At night, surfaces cool by radiating long-wave energy to the cold sky; a low Ψ traps that radiation between the building walls instead, so a taller, narrower canyon cools far more slowly than open ground — the classic mechanism behind why the urban heat island is strongest after dark. A simplified surface energy balance drives both a canyon and a reference rural site through a full day/night cycle:

dT/dt = S(t)·(1−albedo) − k_rad·Ψ·(T−T_sky) − k_conv·(T−T_amb)

where S(t) is solar input (zero at night, peaked at noon), the radiative term scales with Ψ (a low Ψ chokes off nighttime cooling), and a convective term relaxes both sites toward a shared background temperature. The rural site always uses Ψ = 1; only the canyon's Ψ depends on your height/width sliders — the growing gap between the two temperature traces at night is the modelled UHI intensity.

Height H / Width W — reshape the 3D canyon and recompute Ψ live.
Albedo — lighter building/pavement surfaces absorb less daytime solar heat (the "cool roof" strategy).
Simulation speed — how many simulated hours pass per second.

Real-world relevance: this Ψ-based canyon model traces back to Oke (1981) and still underlies modern urban-canopy schemes used in city climate-adaptation planning.

Canyon temp Rural temp

⚠ Couldn't load the 3D engineThree.js failed to load from the CDN. Check your connection and reload.