Urban heat island

What’s a urban heat island? To answer this question we need to start from explaining that air temperature and surface temperature are two different things. Have you ever walked on the beach bare foot? Of course, so you know the difference. The sand can get way hotter than the air. But why? What makes the difference here? The color and the chemical composition of the surface.

Streets and roofs are usually dark and, because of this, they absorb more heat than white objects. Asphalt and concrete is also water resistant. Didn’t you notice that after the rain there’re a lot of puddles here and there? This happens because water can’t pass through the concrete. In our cities, everywhere you look you can see concrete, asphalt, roofs and parking lots. All of this contributes to the urban heat island effect, which explains why cities are usually a few degrees hotter than the countryside surrounding them.

isola di calore

This affects also the night time. During the night buildings and streets release the heat absorbed during the day.
Does this happen even in winter? Yes. Maybe we don’t feel it, but the city is hotter that the surround areas even during the coldest months of the year. This is why, in some cities, snow it’s not that common.