Cities in the Global South have far less green space

As urban populations swell and climate change accelerates, the cooling effects of green spaces in cities become increasingly vital.

A recent study has identified a significant gap in green space – and therefore cooling capacity – between cities in the Global South and those in the Global North. 

Utilizing NASA satellite data, the research underscores the urgent need for equitable urban planning to mitigate the impacts of extreme heat.

Health risks of urban heat

Cities are often hotter than surrounding rural areas due to the urban heat island effect. Dark surfaces like roads, buildings, and sidewalks absorb and retain heat from the sun, raising temperatures in urban environments. 

This exacerbated heat poses serious health threats to city dwellers, including dehydration, heat stroke, and increased mortality rates. Greenery provides natural cooling through shade and the release of moisture into the air, helping to reduce these risks.

Cooling capacity of green spaces in cities

An international research team led by Yuxiang Li, a doctoral student at Nanjing University, analyzed the 500 largest cities globally to compare their cooling capacities. 

The experts employed data from the Landsat 8 satellite, managed by NASA and the U.S. Geological Survey, to assess land surface temperatures during the hottest months from 2017 to 2019. 

The team used the Normalized Difference Vegetation Index (NDVI) to quantify the amount of healthy vegetation in each city. NDVI measures the difference between absorbed red light and reflected infrared light to determine vegetation density from satellite images.

Disparities between Global North and South

The study revealed that cities in the Global South have only 70% of the greenery-related cooling capacity found in cities in the Global North. 

On average, green spaces in Global South cities lower temperatures by about 4.5°F (2.5°C), whereas those in Global North cities achieve a reduction of 6.5°F (3.6°C). 

This disparity intensifies existing problems, as many Global South cities are situated closer to the Equator and are expected to face more frequent and severe heat extremes due to climate change.

“It’s already clear that Global South countries will be impacted by heat waves, rising temperatures, and climatic extremes more than their Global North counterparts,” said Chi Xu, a professor of ecology at Nanjing University and co-author of the study. 

The capacity to adapt to heat is also lower in the Global South, where air conditioning is less common and power outages are more frequent.

The “luxury effect” across cities

Cities in the Global South generally have less green space, reflecting a pattern known as the “luxury effect,” where wealthier areas possess more greenery than poorer ones. 

This trend is observed both within cities and on a global scale. “Wealthier cities also have more urban green spaces than the poorest cities,” Chi noted.

Bridging the gap between cities like Mogadishu, Somalia (the study’s lowest-performing city), and Charlotte, North Carolina (the highest-performing city), is challenging. 

Factors such as dense urban development and arid climates limit vegetation growth in some regions. However, cities can learn from regional leaders in cooling capacity. 

By identifying top-performing cities within their regions, urban planners can set realistic goals to enhance their own green spaces and cooling effects.

Cooling cities with green spaces 

Increasing green space is one strategy among many to improve a city’s cooling capacity. 

“How you utilize green space is really going to vary depending on the climate and the urban environment you’re focused on,” said Christian Braneon, a climate scientist at NASA’s Goddard Institute for Space Studies who was not involved in the study.

Other methods include creating water bodies, installing green roofs, and using lighter-colored materials for roofs and pavements to reflect more sunlight. 

While greener cities in the U.S. and Canada often have lower population densities, this isn’t inherently better for the environment, as it can lead to increased car reliance and larger, less efficient homes.

Implications for future urban development

The global insights from this study enable urban planners to compare and adopt strategies suitable for cities with similar climates or densities. 

“For newly urbanized areas that aren’t completely built out, there’s a lot of room to still change the design,” Braneon emphasized.

By proactively integrating green spaces and other cooling measures into urban planning, especially in rapidly developing regions, cities can significantly enhance their resilience to rising temperatures. 

Addressing the disparities in urban green spaces is crucial for protecting vulnerable populations in the face of escalating climate challenges.

The study is published in the journal Nature Communications.

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