A new study has found that cities in the Global South are increasingly vulnerable to extreme heat due to a lack of green spaces.
The study, which was led by an international team including Nanjing, Exeter, Aarhus and North Carolina State universities, found that cities in the Global South have just 70% of the cooling capacity of more developed cities, due to a lack of urban greenery amidst global warming’s intensifying effects..
This means that as temperatures rise, the ‘urban heat island’ effect of these cities becomes more severe, leading to heat-related illnesses and death.
According to the researchers, there is ‘vast potential’ to accelerate urban cooling in the Global South through the introduction of more urban green spaces, as well as reduce inequality.
“Urban greenery is a really effective way of tackling what can be fatal effects of extreme heat and humidity,” commented Professor Tim Lenton, of the Global Systems Institute at the University of Exeter. “Currently, the people dying due to climate change are often in the slums of cities in the Global South, such as the hottest parts of India.
“Our analysis suggests green spaces can cool the surface temperature in the average city by about 3°C during warm seasons – a vital difference during extreme heat.”
The study incorporated satellite data on the world’s 500 largest cities to assess their cooling capacity, in other words the extent to which urban green spaces reduce a city’s surface temperatures.
The Global South is a term to described developing and under-developed nations in Africa, Latin America and much of Asia, many of which are located in areas most at risk from extreme heat.
Cooling capacity
The findings revealed that the top ten cities with the highest cooling capacity are all located in the United States. Charlotte and Raleigh-Durham ranked first, followed by Kansas City and Baltimore. This is partly attributed to the lower population density in many US cities, which, despite contributing to urban sprawl, also provides more green spaces that help cool down surface temperatures.
At the opposite end of the spectrum, Mogadishu in Somalia was identified as the city with the lowest cooling capacity, followed by Sana’a in Yemen and Rosario in Argentina. Interestingly, Chicago ranked fourth-lowest, with a cooling effect of less than 1°C.
“As well as Global South cities lagging behind in terms of cooling capacity, the cooling benefit for an average resident is 2.2°C – compared to 3.4°C for a city dweller in the Global North,” commented Professor Chi Xu, of Nanjing University.
“The differences are mostly due to quantity of vegetation, but efficiency of cooling is also better in the Global North – possibly due to management of green spaces and different tree species.”
‘Not an easy task’
Elsewhere, Professor Rob Dunn, of North Carolina State University, added that it “won’t be easy” to enhance urban greenery in many cities, with the cost of doing so often prohibitive.
“Yet, it will be key to making cities liveable in the immediate future,” he noted. “Also key will be working to prevent the loss of green space in those cities that have it, or at least that have a little. Changes could include ground-level green spaces and vertical and rooftop gardens, or even forests, to help protect city people from extreme heat.”
The full study was published in the journal Nature Communications, and is entitled Green infrastructure provides substantial but unequal urban cooling globally.
