This model computes a surface energy balance, Q* = K↓(1−α) + L↓ − L↑ − QH − QE, separately for a city and its surrounding countryside, then shows the resulting temperature cross-section and 24-hour profile. Because urban surfaces reflect less sunlight (lower albedo) and store heat in concrete and asphalt, the city core runs warmer than the rural surroundings — the classic urban heat island.
A side-by-side temperature cross-section and time-of-day profile comparing an urban core against rural land, driven by differences in albedo, vegetation cover and city size.
Adjust City Size, Vegetation Fraction, Urban Albedo, Rural Albedo and Time of Day sliders, and watch ΔT (UHI intensity), Urban T and Rural T update in the stat rows.
Urban surfaces typically have an albedo of just 0.1–0.2 versus 0.3–0.4 for vegetated rural land — that missing reflected sunlight is absorbed as heat and re-released at night, which is why cities often stay hottest well after sunset.
It's the temperature difference between the simulated urban core and the surrounding rural area at the selected time of day — the standard metric used by climatologists to quantify how much hotter a city is than its countryside.
Plants cool their surroundings through evapotranspiration (the QE term in the energy balance) and typically have higher albedo than pavement, so raising the vegetation slider reduces both stored heat and absorbed solar radiation.
Solar input (K↓) peaks at midday and drops to zero at night, but concrete and asphalt release stored heat slowly after dark, so the urban-rural gap (ΔT) often grows largest in the evening and overnight, not at noon.
Albedo — the fraction of sunlight a surface reflects — differs sharply between dark urban materials (asphalt, roofing) and lighter vegetated or soil surfaces, so the model needs both values independently to compute each region's absorbed radiation.
Larger urban footprints hold more total stored heat and take longer to exchange energy with surrounding air, which is why bigger cities in the slider tend to show a larger and more persistent ΔT than small ones with identical materials.