A recent global study conducted by the Joint Research Centre looks at the difference between surface temperatures of urban areas and their neighbouring rural areas in summer.
Worldwide, more than half of the people live in cities, and the share of city dwellers is projected to grow further. Cities often suffer from ‘heat islands’, the phenomenon of temperatures being higher within cities than in neighbouring rural zones. This amplifies the effect of heatwaves in cities and increases the risk to human health.
Scientists at the European Commission’s Joint Research Centre examined the difference between land surface temperatures in urban areas with a population over 50,000 people and in their rural surroundings in summer between 2003 and 2020.
Working with satellite data, scientists measured that surface temperatures in cities were sometimes up to 10-15°C higher than in their rural surroundings. The study also estimated that the temperature in extreme heat islands in cities around the world has risen on average by 1°C in since 2003.
The global scale of the study and high-resolution of the spatial analysis make it possible to compare cities in different climate zones and even different parts within megacities.
Hotspots and cooler areas within global megacities
Across global megacities, such as Tokyo, New York, Paris and London, the study observed a very high intra-city variability in temperature. Hotspots are often found in industrial areas, where waste heat, the use of dark construction material and absence of vegetation can result in very high land surface temperatures. For example, in Paris hotspots are found east of Saint-Denis and near Chevilly Larue, around large industrial complexes.
The study highlights that slums can also form hotspots of heat due to their chaotic, dense and unregulated urbanisation. Intense heat exposure, combined with poverty, poor housing conditions and reduced access to cooling options poses serious health threats to people.
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