Southern cities lack refreshing green spaces

Cities in the global South are more exposed to extreme heat because they lack cooling green spaces, a new study has found. The study found that cities in the global South have only 70% of the “cooling capacity” provided by urban green spaces in the global North. The study, published in the journal Nature Communicationsis titled “Green infrastructure provides substantial but uneven urban cooling globally.”

With rising temperatures and the “urban heat island” effect making cities warmer than rural areas, heat-related illnesses and deaths are becoming more common in cities. Urban green spaces can help reduce this risk by cooling outdoor environments and providing vital refuges.

The research, led by an international team including Nanjing, Exeter, Aarhus and North Carolina State Universities, finds there is “vast potential” to improve urban cooling in the Global South and reduce inequality.

“Urban greenery is a highly effective way to combat the sometimes fatal effects of extreme heat and humidity,” said Professor Tim Lenton, from the University of Exeter’s Global Systems Institute.

“Currently, people dying from climate change often live in the slums of cities in the global south, such as in the hottest parts of India. Our analysis suggests that green spaces can cool the surface temperature of an average city by about 3°C ​​during hot seasons, a vital difference in extreme heat.”

The cooling effect of urban green spaces, especially urban forests, is due to shading and cooling by transpiration (evaporation of water).

The new study used satellite data on the world’s 500 largest cities to assess “cooling capacity” – the extent to which urban green spaces cool a city’s surface temperatures.

The top ten cities in terms of cooling capacity are all in the United States, with Charlotte and Raleigh-Durham leading the way, followed by Kansas and Baltimore. Many American cities have low population densities, which leads to urban sprawl issues, but this brings benefits in terms of green space and cooling.

Mogadishu, Somalia, is the city with the lowest cooling capacity, followed by Sanaa in Yemen and Rosario in Argentina. Chicago is the fourth lowest, the only US city on the list with a cooling capacity below 1°C.

“Refreshing advantage”

The countries of the South, which include Africa, Latin America and much of Asia, are home to the areas most exposed to extreme heat.

A previous study found that current climate policies would expose more than a fifth of humanity to dangerously high temperatures by 2100, with populations most at risk in India and Nigeria.

The new study assessed population density and location to estimate the “cooling benefit” received by the average citizen, since green spaces are often found in a city’s wealthiest neighborhoods.

According to Professor Chi Xu of Nanjing University, “Southern cities lag behind in terms of cooling capacity, but the cooling benefit for an average resident is 2.2°C, compared with 3.4°C for a northerner. The differences are mainly due to the amount of vegetation, but cooling efficiency is also better in the north, perhaps due to the management of green spaces and different tree species.”

Professor Jens-Christian Svenning, from the Centre for Ecological Dynamics in a New Biosphere (ECONOVO) at Aarhus University, said: “The good news is that this nature-based cooling solution can be significantly scaled up in the Global South, helping to combat future heat stress for billions of people.”

Professor Rob Dunn of North Carolina State University said: “Regreening cities will not be easy. It can be costly in the short term. Yet it will be essential to making cities liveable in the near future. It will also be essential to work to prevent the loss of green space in cities that have it, or at least some of it.”

“Changes could include ground-level green spaces, vertical and rooftop gardens, and even forests, to help protect city dwellers from extreme heat.”