Urban heat island

An urban heat island is the tendency of a dense, paved city to stay noticeably hotter than the countryside around it — often several degrees warmer, and most stubbornly at night. Dark asphalt, concrete and roofs soak up sunlight all day and radiate it back after dark, while traffic, industry and air-conditioners add their own waste heat.

Because the effect stays invisible until people suffer in a heatwave, cities first try to measure it. Gründau publishes a live community heat map fed by LoRaWAN sensors at playgrounds across the town. Cooling things down then means shade, greenery and less trapped traffic. A superblock like Barcelona's Sant Antoni pushes cars to the perimeter and greens the freed-up squares, and Singapore's Marina Bay district cooling network cuts customer cooling energy by more than 40%, which also means fewer AC units dumping heat into the street.

The honest catch is fairness and time. Heat islands hit hardest in poorer neighbourhoods with the least tree cover, trees take years to mature, and mechanical cooling can simply move the energy burden elsewhere. Measuring the problem is easy; funding the green infrastructure that fixes it is not.