By Mark Watts, Executive Director of C40 Cities

High angle view on Montreal downtown
© Pierre Ogeron / Getty Images

This week’s COP15 biodiversity summit is crucial for the future of life on our planet. At COP27, the architects of the Paris Agreement warned that limiting global heating to 1.5°C is impossible without adequate protection and restoration of ecosystems. Nature has an absolutely vital role to play in combatting the climate crisis – including in urban environments.  

Many of us will instinctively appreciate the way that nature can make the city a more pleasant place to live and work. For those of us who have experienced pandemic lockdowns in cities and have been fortunate enough to have access to green space, urban nature has often proved to be a lifeline. However, green infrastructure in the built environment can offer enormous benefits beyond health and leisure for urban residents. Cities can implement nature-based solutions that build resilience to climate impacts, absorb carbon, improve biodiversity, boost people’s wellbeing and create good, green jobs.

One simple but effective intervention that global cities are implementing is the use of tree cover and green corridors, which provide evapotranspiration and shade for cooling and protection from rising urban heat. In Colombia, Medellín has planted 30 green corridors across the city to reduce urban heat and improve biodiversity and air quality. This has resulted in a reduction of the urban heat island effect by two degrees since the programme began three years ago. Melbourne’s ‘Urban Forest’ strategy, which is working to increase the city’s tree canopy from 22% to 40% by 2040, is designed to increase the diversity of tree species, as well as reduce inner-city temperatures. Mumbai is developing an urban forest as part of its plan to reduce the land surface temperature around some of the city’s major infrastructure, such as its metro line. The project will include stone pathways, a pond and over 140 species of trees.

Nature-based solutions are also an important tool for flood prevention in cities. Freetown, the capital of Sierra Leone, has experienced devastating flooding and landslides due to heavy rains and deforestation in recent years. Since 2020, the city’s #FreetownTheTreeTown initiative has planted and verified more than 500,000 trees, prioritising areas at risk of landslides, riverbanks and low-income areas that are most in need of re-greening. An innovative tree-health tracking app has ensured a long-term survival rate of 80%. In addition to protecting the city from floods, the trees represent a valuable carbon sink.

The ‘Freetown The Treetown’ project on Wednesday, Oct. 5, 2022 in Freetown, Sierra Leone. The city has taken action to reduce landslide and flooding risk through the “Freetown the TreeTown” initiative, which aims to increase the city’s green space and vegetation cover. (Michael Duff/AP Images for C40)
© Michael Duff / AP Images for C40

Wuhan’s ‘sponge city’ programme, which makes use of green infrastructure to prevent flooding, is CNY 4 billion (US$600 million) cheaper than upgrading the city’s drainage systems. The city has initiated 389 sponge city projects, including urban gardens, parks and green space, which are designed to allow water to infiltrate when it rains and direct water away from urban areas during flooding. As well as preventing flooding, the project brings multiple co-benefits – the area around the city’s Yangtze River Beach Park sequesters 724 tonnes of carbon annually, while temperatures in the park can be three degrees cooler than the rest of the city. 

Restoring riverbanks is one of the most dynamic ways for cities to generate benefits for both people and wildlife. Portland is restoring the watershed along the Crystal Springs Creek by planting 7,220 trees and shrubs. The estimated flood reduction benefits of the project are between US$160,000 and US$380,000 per hectare, and for the first time in decades scientists have recorded spawning pairs of three fish species that were previously thought to have been driven out of this ecosystem. 

Investing in nature also creates good, green jobs. In South Africa, Ethekwini’s Transformative Riverine Management Programme is improving resilience and creating thousands of green jobs. Analysis by C40 in 2020 found that investment in a green and just recovery would create over 50 million good, sustainable jobs by 2025, particularly in South Asia and Africa.  

Crucially too, there is evidence that contact with natural environments, such as parks, is associated with better health and wellbeing. A study in Toronto, Canada, found that adding just ten trees to a city block has a huge impact on people’s perceptions of their health and well-being, equivalent to the effect of earning $10,000 more per household or being 7 years younger. A number of cities have put in place targets to increase people’s access to greenery:  Lisbon plans for 90% of the population to be less than 300m from a green space bigger than 2,000m2 by 2030, while Los Angeles is aiming for at least 65% of residents to live within half a mile of a park or open space by 2025. Quito has set a target to increase its green space to at least 20m2 per resident by 2030, with a focus on the equitable distribution of green space across the city.

It is truly inspiring to see how cities are bringing nature into urban environments, improving quality of life for residents, building resilience, mitigating the climate crisis and boosting biodiversity. As many of the world’s cities are demonstrating, the future of cities is green.

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