Summer is drawing to a close according to the calendar, but not in terms of the heat, which continues in much of the world. High temperatures have most severely affected large cities in southern regions, and a new scientific study sought to uncover what these cities lack to successfully cope with heat waves.
The study, published in Nature Communications, reveals that cities in the Global South are more exposed to extreme heat due to a lack of cooling green spaces. Compared to cities in the Global North, they only have 70 percent of the “cooling potential” provided by urban greenery.
An international team of experts used satellite data from the 500 largest cities in the world to assess the “cooling capacity”—the extent to which urban green spaces cool the surface temperatures of a city. The ten cities with the highest cooling capacity are located in the USA, as many cities in the United States have low population density, giving them an advantage in terms of green space.
Mogadishu in Somalia has the lowest cooling capacity, followed by Sana’a in Yemen and Rosario in Argentina. Chicago is the only American city on the list with a cooling capacity below 1°C.
The Global South, which includes Africa, Latin America, and much of Asia, contains areas most vulnerable to extreme heat. A previous study showed that current climate policies will leave more than one-fifth of humanity exposed to dangerously high temperatures by the year 2100, with the highest risk population in India and Nigeria.
The new study goes further by estimating the “cooling benefit” an average citizen receives, showing that the cooling advantage for an average resident in the Global South is 2.2°C, compared to 3.4°C for a resident of a city in the Global North. These differences are mainly due to the amount of vegetation and the efficiency of cooling, which is better in the Global North.
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The Importance of Nature-Based Solutions
The analysis suggests that green spaces can lower the surface temperature in an average city by about 3°C during summer, a crucial difference during periods of extreme heat. The cooling effect of urban green spaces, especially urban forests, is caused by shading and transpiration cooling.
“Urban greenery is a very effective way to combat what could be the fatal effects of extreme heat and humidity,” said Professor Tim Lenton, one of the study’s authors.
With rising temperatures and the effects of the “urban heat island,” heat-related illnesses and mortality in cities are becoming more common. Experts emphasize that nature-based solutions can significantly reduce future heat stress for billions of people.
Therefore, re-greening urban environments and preserving existing greenery is crucial to making southern cities livable in the near future.
