EU Cities and Heat Extremes
This policy brief outlines different ways to tackle heat extremes in cities, suggesting strategic recommendations, best practices, and analytical approaches that local authorities can make use of. Heatwaves and Urban Heat Islands Heatwaves and their local manifestations are some of the most severe consequences of climate change and the increase in frequency and intensity of recordbreaking temperatures is projected to continue. Around half a trillion euros over the past 40 years
have been accounted for, together with between 85 000 and 145 000 human fatalities across Europe because of extreme weather and climate-related events. Among these fatalities, more than 85% as the result of heatwaves between 1981 and 2020.
In the last summer periods, many densely populated areas experienced record heat. Notably, of throughly 10 000 cities in the world, nearly half faced an increasing trend in heat exposure between 1983 and 2016. For example, recent studies revealed that potential exposure to extreme heat among urban dwellers exceeded 1.7 billion people. Consequently, monitoring such exposure is very relevant to address risk reduction. Heatwaves refer to prolonged, extremely high
temperatures that can cause the microclimatic phenomenon known as ‘Urban Heat Island’ (UHI). The consequences of increasing temperatures are exacerbated in cities where health threats and other severe risks are more likely to happen. Notably,
the urban warming component is on the increase and local temperatures can go up, whereby cities become hotter than surrounding suburban regions and rural areas, causing urban overheating.
The reason why temperatures within urban areas can become generally higher than their surroundings may be attributed to more sealed surfaces (which absorb heat during the day and release it at night), and higher density of both people and heat-emitting infrastructures. These factors combine with often low ventilation and fewer green areas and waterways to provide cooling. By altering the nature of the city’s surface, and generating large amounts of anthropogenic heat, cities modify the microclimate and air quality, increasing their ecological footprint.
A UHI also traps atmospheric pollutants (‘urban pollution island’) which in turn deteriorate the quality of life and have a direct impact on energy demand. In cities characterised by a high density of built surfaces, peak temperatures may be up to 10°C higher than in surrounding rural areas with an average between 4 and 6°C. The intensity of an UHI is usually quantified through the ‘Land Surface Temperature’ (LST) and is referred to as ‘Surface Urban Heat Island’ (SUHI), leading to a strong relation with landscape patterns. Notably, land cover types represent an important factor influencing local temperatures, due to the significant difference between impervious and vegetated surfaces.
source :
https://publications.jrc.ec.europa.eu/repository/handle/JRC137891#