Geography
Why Land Surface Temperature Varies Within a Single Metropolitan Area
Quick fact
On a sunny summer afternoon, a dark asphalt parking lot can be 30–40°C hotter than the air temperature, while a shaded, grassy park may be closer to air temperature, creating a temperature difference of more than 10°C across just a few hundred meters.
Why this is interesting
When you step out of the subway on a scorching summer day, the air feels heavier and hotter than just a few blocks away in the park. Why can two places in the same city feel like different climates?
Read the full explanation
Understanding Why Land Surface Temperature Varies Within a Single Metropolitan Area
Imagine a city as a patchwork quilt of surfaces: concrete sidewalks, metal rooftops, asphalt roads, brick walls, glass windows, lawns, and tree canopies. Each of these materials interacts with sunlight differently. Dark, rough materials (like asphalt) absorb a large portion of incoming solar radiation, becoming very hot, while light-colored, shiny surfaces (like white concrete or glass) reflect more sunlight, staying cooler. But that’s only part of the story. The shape of the city also matters: tall buildings create deep 'canyons' that trap heat, and they block wind and shade each other differently throughout the day. Water and vegetation act as natural air conditioners: they absorb water and release it through evaporation (from soil and leaves), pulling heat from the air and cooling the surroundings. Even human activities—cars engines, industrial processes, air conditioning units—dump extra heat into the street. In this way, every block has its own microclimate, and the temperature you feel at a bus stop is the product of these local factors combined with the regional weather.
A deeper explanation
The variation in land surface temperature (LST) arises from the spatial distribution of surface energy balance components. The key equation is: Net radiation = sensible heat flux (warming the air) + latent heat flux (evaporation) + ground heat flux (stored in the ground). Surfaces with high albedo (reflectivity) receive less net solar radiation, so they warm less. Dark pavements have low albedo (~0.05–0.1) and high heat storage capacity, absorbing heat during the day and releasing it long after sunset—this is the urban heat island's core. Vegetation and water have high latent heat flux because they use the absorbed energy to evaporate water, cooling the surface (a process called evaporative cooling). Urban geometry—building height, street width—modulates solar exposure and ventilation: narrow street canyons trap radiation through multiple reflections and reduce wind speed, keeping heat stored between buildings. Additionally, anthropogenic heat from transportation and buildings adds a direct thermal input. Therefore, LST varies because different urban land uses have different radiative properties, thermal inertia, and moisture availability, producing a mosaic of cool and hot spots that can be observed on satellite thermal imagery or felt on the ground.