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The urban heat island effect
Green spaces in cities mitigate the effects of pollution and can reduce a phenomenon known as the urban heat island effect, which refers to heat trapped in built-up areas.
The urban heat island effect appears in towns and cities as a result of human activity. The heat generated by people, transport, shops and industry is trapped in the narrow roads and concrete structures, unable to escape to the atmosphere. This can bring the temperature in urban areas up 3-4°C higher than the surrounding countryside, and with that comes a vicious cycle.
Increased temperatures in summer leads to an increased demand for cooling. This expands our energy consumption, which in turn intensifies fossil fuel consumption, increasing pollutants in the air and harmful smog on our streets.
Hotter pavements also damage the water cycle. In summer, surface temperatures can be a staggering 50°C hotter than the surrounding air, and that heat is transferred to the rainwater that drains into our sewers, which in turn raises water temperatures as it is released into streams, rivers, and lakes. This can be destructive to aquatic ecosystems, as changes in water temperature can be stressful or even fatal for marine life.
City life: Why are green spaces important? - Natural History Museum (nhm.ac.uk)

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