What is the urban heat island effect?
Maybe you have noticed that when entering an urban area, the air suddenly feels warmer, even unpleasantly hot, compared to outside the city. Then you have experienced the urban heat island effect. UHIs occur when natural land cover (e.g., meadows, forests, lakes, riverbanks, etc.) are replaced by the densely sealed surface of a city. Streets, buildings, parking lots, pavements, and building materials absorb and retain heat. They also prevent rainwater from being absorbed into the ground. Consequently, the rainwater evaporates quickly from such surfaces, and without any plants to ensure transpiration, no cooling effect occurs.
As a result, the temperature in an urban area is considerably higher than in the rural area, especially during summer and in warm regions, and builds an urban heat island. For example, in summer, the temperature of New York City is 4°C higher than its surrounding rural area. This may seem a small difference, but already small increases in temperature can have negative consequences for humans and nature.
Heat: A danger for the environment and public health
Heat Islands Increase Energy Consumption
With every 2 degree in temperature rise, the electricity demand for air conditioning increases 1-9% percent, according to the United States Environmental Protection Agency.
UHIs exacerbate extreme heat events. This is not only problematic as it can lead to electricity shortages and blackouts during such events, but higher electricity expanses mean also higher consumption of resources to produce energy. With the continuously high share of fossil fuels in energy production, an increase in electricity use leads to an increase in the emission of air pollutants and greenhouse gas emissions.