The city has a higher average temperature throughout the year than the country. The difference is 1 to 3 degrees. Scientists call this effect an “urban heat island.” The effect is greater at night. The difference between the city center and the countryside is about 5 degrees on a midsummer night, and in extreme cases more than 10 degrees.
Why is the city warmer at night?
Materials such as concrete, dark asphalt or stone predominate in the city. These materials absorb heat during the day and, most importantly, are very good at storing energy, much better than undeveloped land. The city functions as a battery that is charged with thermal energy from the sun during the day. At night, energy is emitted from the streets and buildings. As a result, the air cools less. In addition, the winds in urban canyons at night are significantly less than in the countryside.
Urban heat island is a well-studied effect, and the counter-recipes are well known. Building materials should be used in such a way that they absorb energy as poorly as possible during the day. This can be achieved with a light color, for example. White reflects sunlight and cannot be stored with it. The countries of the south already know this, so many homes in Greece are white.
Some examples of reflexology. The black plate reflects about 10% of sunlight, so 90% is converted into heat. Red roof tiles reflect 10 to 35% and white reflect 50 to 90% of sunlight.
Green spaces and trees are also effective. On the one hand, it cools by shading, but it’s also a natural air conditioner. Vegetation evaporates water. This process requires energy, just like boiling water. This energy is derived from the surrounding air. Evaporation cools.
If a city stores a lot of energy, it uses the energy for cooling with air conditioning systems. A cooler city also helps save energy in the summer. For every degree less ambient temperature, 4% less electricity is used for the air conditioning system.
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