Urban Heat Island (UHI) intensity

Urban heat island (UHI) is a phenomenon, where urban areas are significantly warmer than their surrounding rural areas. This occurs mainly due to the built environment (roads, buildings) that absorbs and retains heat during the day and slowly releases at night. Lack of vegetation in urban areas limits the natural cooling through shade and evaporation. UHI increases the exposure to heat among urban populations. Heat exposure can lead to heat exhaustion, heatstroke, and worsening many chronic diseases.

Short method description

This indicator tracks ambient urban heat island (UHI) density by calculating the area-weighted difference of daily temperatures between urban and rural zones during summer months in 820 cities in 29 European countries, from 2003-2020.

Main findings

​​ European cities​ presented an​​ annual average of​ 7.7 days with​ urban heat island​ intensit​y​​ higher than ​​1·5°C ​​from 2003-2020.

Caveats

Difficulties calculating the UHI intensity originates from the definition of city boundaries, which often reflect administrative boundaries with large unpopulated areas and significant elevation gradients that could affect the temperature. Therefore, an elevation filter was applied, to minimize the overestimation of UHI intensity.