Governments and private sector urged to invest in cool cities

Development Asia, the Asian Development Bank’s knowledge collaboration platform for sharing development experience and expertise, best practices, and technologies relevant to sustainable development goals, has called for more integrated planning, equitable access, community input, and local adaptation for fair, effective results on urban cooling through nature-based solutions (NbS). The platform pointed out that extreme heat is an invisible but increasingly tangible climate risk, as shown by record temperatures earlier this year across Asia, and those living in cities are worst affected. As global temperatures rise, extreme heat events (heatwaves) are becoming more frequent and severe. Cities, which are affected by urban heat island effects, face heightened temperatures. Projections show that several cities in Asia and the Pacific could see temperatures rise by up to 4°C if greenhouse gas emissions remain unchanged. Urbanisation and growth in these regions compound the impact of rising temperatures. By 2050, Asia’s urban population is expected to grow by 50%, adding 1.2 billion people, while Pacific urban populations could reach 51% of the population. This growth will replace natural environments – essential for cooling – with heat-trapping surfaces, said Development Asia. “Heat impacts vary across cities, often adding to equity and environmental justice issues. Green spaces, usually linked to wealth, are unevenly distributed. Cooler, greener neighbourhoods are often home to high-income residents, while informal, lower-income areas experience more extreme heat. In Bandung, Indonesia, a study revealed a temperature difference of up to 7°C between the hottest and coolest neighbourhoods. Impoverished communities, including women in developing countries, are especially vulnerable. The Asia-Pacific region must find ways to implement scalable cooling solutions that ensure equitable access to thermal comfort for its growing urban populations,” stressed the platform. Nature-based solutions for cooling such as street trees, urban parks, green roofs and wetlands are part of the answer, said Development Asia. “These solutions provide cooling by offering shade, promoting evapotranspiration, and acting as heat sinks that mitigate the urban heat island effect. For instance, tree canopies and vegetation can reduce peak summer temperatures by 1° to 5°C,” it pointed out. Maximum cooling is achieved when green and blue solutions are combined, but approaches must be tailored to local conditions. For example, dense tree canopies may trap heat and increase humidity, so pairing them with wind solutions could help disperse hot air. Development Asia said that nature-based solutions are particularly relevant in developing countries due to their cost-effectiveness and multiple benefits. “In addition to cooling, well-designed NbS can help control erosion, improve health and contribute to climate targets. Studies show that green and blue infrastructure, combined with urban design and reflective surfaces, can offer up to 12 times their cost in net benefits,” said the platform. Nature-based solutions can also offer co-benefits for carbon sequestration, biodiversity value and health benefits. For example, a green roof can support biodiversity by providing habitat and attracting pollinators. As urbanisation accelerates, cities across Asia and the Pacific have embraced nature-based solutions for cooling and broader sustainability. Development Asia cites three examples of cities in Asia that have already made great strides in this area: Singapore, Kochi in India and Seoul in Korea. “Singapore exemplifies how green buildings can cool cities. City planning incentivises greening the built environment through sky gardens, green facades, landscaping, water features, and urban farms. Green infrastructure promotes evapotranspiration, creates shade, and increases the albedo of built surfaces. Today, 40% of Singapore is green, with a target to green 80% of its buildings by 2030 under the City in Nature vision. “Green roofs and walls, depending on vegetation type and density, can reduce surface temperatures by 17°C, contributing to ambient temperature drops of up to 5°C. A key driver of this is the Landscaping for Urban Spaces and High-Rises (LUSH) programme, initiated in 2009. LUSH mandates on-site greenery equivalent to the size of the development and incentivises rooftop greenery through gross floor area exemptions. The government also covers 50% of the costs for green roofs and facades on existing buildings,” stated the platform. OF Kochi Development Asia states: “Despite their broad potential, nature-based solutions are often overlooked in city cooling strategies. Key barriers include a lack of supportive policies, financial constraints and limited institutional capacity. Addressing these challenges requires a multi-pronged approach that maximises NbS benefits and integrates them into broader heat action plans. This must involve reducing waste heat (e.g. from transport and buildings), addressing cooling needs efficiently and ensuring equitable access to thermal comfort. Key considerations for incorporating NbS into urban cooling strategies include: Integrated planning: A systems approach ensures NbS are complemented by other solutions to maximise their benefits; Equity: Cooling solutions must be distributed fairly, with heat equity embedded in planning to prevent future injustices; Community participation: Involve women and vulnerable groups in designing and implementing cooling programs that deliver real benefits; and, Local solutions: NbS should be tailored to local climates, needs, and traditional approaches (e.g. architecture). Studies suggest that 30% of cities should be dedicated to green or blue spaces. “Achieving this requires enabling strategies like raising awareness, building institutional capacity and securing financing. It also involves assessing current natural assets and identifying vulnerable communities,” added the platform. “In developing countries, protecting existing green spaces from development is the most effective way to maintain cooling,” argued Development Asia. “Creating a cooling-friendly urban form requires time and sustained effort. In the near term, practical, no-regret actions to build resilience to heat stress through NbS include: Establishing champions and authorities to protect and enhance green and blue spaces; Conducting baseline assessments of green and blue spaces and identifying vulnerable communities; Investing in green and blue infrastructure, especially in public areas. “Tree planting is perhaps the simplest and most effective action to reduce urban heat –provided the right trees are planted in the right places as part of a coordinated city-wide greening effort. Steps taken today will help future generations benefit from NbS for cooling,” stated the platform. “Cities in Indonesia, Malaysia and the Philippines can be up to 5.9°C warmer than nearby areas. As cities grow, more people will face heat extremes – by the 2050s, this could be 700% more than today. Energy use, especially air conditioning, worsens the situation by straining the electric grid during extreme weather and creating a feedback loop by adding heat,” pointed out the research body. “In many Asian and Pacific cities, humidity compounds the heat. Humidity reduces the efficiency of heat convection, trapping it in water vapor instead of letting it evaporate. It also limits the body’s ability to cool through sweating, increasing discomfort. Addressing humidity is crucial in finding cooling solutions, as some options may increase moisture in the air. “As cities warm, it’s essential to provide equitable access to cooling without worsening the urban heat island effect. Reducing the need for cooling and cutting emissions is vital to mitigating global warming,” concluded Development Asia.

Governments and private sector urged to invest in cool cities

Singapore, Kochi and Seoul lead the way in nature-based solutions for cities

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