What is Urban Heat Island (UHI)?
Urban heat island is a term describing the effect on cities and urban areas that are hotter than nearby rural areas. It is the difference in mean air temperature of a city compared to the surrounding countryside that can be some 1.8–5.4°F (1–3°C) higher on annual average and around 22°F (12°C) during the evening according to the American EPA (www.epa.gov). This effect is the result of building roofs as well as roads, sidewalks, parking lots and other gray infrastructure blocking the heat coming from the ground from rising and dispersing into the air. At night heat remains trapped lower to the ground which makes the air temperature warmer. Side effects include poorer air quality, due to higher concentrations of pollutants in the air (waste products from people, industry, vehicles) and lower water quality.
Current extreme heatwaves are contributing to even bigger UHI effects
Southern and Southwestern Europe are facing extreme heatwaves this July, which affect communities by increasing summer’s peak energy demand, air conditioning costs, greenhouse gas emissions, air pollution, even heat-related illness and mortality rates. The heatwave, enveloping Spain, France, Italy, Switzerland, Austria and the Balkan Countries, has continued since late June and is expected to continue in the near future. In several cities temperatures are rising to as high as 40°C. Those suffering the most are the densely populated and built-up urban areas. And as people are trying to ease the heat in their homes by using electric fans and air-conditioning, they are at the same time contributing to an even warmer urban heat island effect. And so the process comes full circle.