Urban heat island facts for kids

An urban heat island, or UHI, is what happens when a city is warmer than the area around it. It happens because things in cities like concrete take longer to give off heat than things like trees, which are common outside of cities. The urban heat island effect is stronger at night and when there is not much wind. Cities can be 3°C warmer than nearby countryside.

In country areas, a large part of the incoming solar energy goes to evaporate water from vegetation and soil. But cities have less vegetation and soil. In cities, most of the sun’s energy is absorbed by urban building and asphalt paving. During warm daylight hours, there is less evaporative cooling in cities than in country areas. So, surface temperatures rise higher in cities than in country areas.

Also, vehicles, factories, and industrial and domestic heating and cooling units give off more heat in cities. This problem is growing. This effect causes the city to become 2 to 10^o F (1 to 6^o C) warmer than surrounding rural areas.

Images for kids

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  echanism of Urban heat island

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  Thermal (top) and vegetation (bottom) locations around New York City via infrared satellite imagery. A comparison of the images shows that where vegetation is dense, temperatures are lower.

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  Monthly variation in day-time UHI in the pre and post-monsoon seasons. (a–d) Day-time UHI (°C) for the post monsoon season (October–January), (e–h) day-time UHI for the pre-monsoon season (February–May). All the values were estimated for LST and NDVI data from MODIS Aqua sensor. The red and blue colours indicate positive and negative values of UHI. The size of the circles represents the intensities in °C. The coloured regions show different climate zones based on Koppen Geiger climate classification map. The dominant climate regions across India is classified as: Cold Desert (CD), Warm Mediterranean (WM), Cool Continental (CC), Tropical Monsoon (TM), Tropical Savannah (TS), Warm Semi-arid (WSA), Cold Semi-arid (CSA), Warm Desert Climate (WDC), Warm Humid Subtropical (WHS), Humid Continental (HC) and Hot-Humid Subtropical (HHS).

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  Image of Atlanta, Georgia, showing temperature distribution, with blue showing cool temperatures, red warm, and hot areas appear white.

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  Green roof of Chicago City Hall.

See also

In Spanish: Isla de calor para niños