Exclusive: the role of nature-based systems in addressing urban heatwave and flood risk

As experts and leaders meet in Montreal for two weeks of discussions focussing on the biodiversity crisis, we take a look at how the role of nature-based solutions are crucial to help address the various physical risks cities face, namely heatwaves and floods. 

According to the United Nations, the global population is expected reach 9.8 billion by 2050, with 70% living in cities. Given that 2050 is also a target date for achieving net zero emissions,  ensuring cities are healthy and sustainable places to live is imperative.

Nature-based solutions are sustainable design, management, and engineering practices that weave natural features or processes into the built environment to benefit both people and nature. They leverage nature, such as trees and soft landscaping, to address multiple issues at once, including water quality improvement, coastal property protection from storm surges, and erosion prevention by stabilising shorelines and hilly terrains.

Cities can enjoy numerous benefits by adopting nature-based solutions designed to address specific issues. These range from providing shade during warmer months and habitat for pollinators and wildlife, and filtering air pollutants, to offering an increased sense of wellbeing to people by incorporating greenery and additional recreational spaces. Heat-retaining materials, from concrete and asphalt to steel and glass, are ubiquitous in cities, and vegetated spaces can help reduce the risk of extreme heat. The benefits of nature-based solutions also extend to urban flood risk mitigation.

Urban flood risk and heatwaves on the rise

Global warming has supercharged the water cycle, leading to increasingly severe and frequent rain events all over the world. This has caused floods of unprecedented scale that have severely impacted communities, homes and investments. Swiss RE Institute estimates insured losses for natural disasters globally reached $35 billion in the first six months of 2022, a 22% increase on the 10-year average.

Due to the prevalence of impervious surfaces, lack of natural drainage paths, and high density, urban areas are particularly vulnerable to the impacts of sudden, extreme downpours, leading to flash floods. Cities with antiquated wastewater systems are particularly susceptible. Left with limited drainage for the water to go during extreme downpours, minor localised floods in these cities often transform to major events.

Urban floods become localised because of small-scale factors such as slight changes in topography and elevation, stormwater management infrastructure, and building design. Strategically placed nature-based solutions, such as green spaces for runoff control, can contain localised floods and keep them from expanding.

Many cities that deal with flash floods also suffer from extreme heat and urban heat island effect, aggravated by the same non-pervious paved surfaces that radiate the heat back to the environment and people. This could also be mitigated by adding more planting and green spaces, creating more opportunities for natural cooling, as vegetation can deflect radiation from the sun and release moisture into the atmosphere. 

For both flood risk and extreme heat mitigation, nature-based solutions are a logical, lower cost option which brings a multitude of other benefits into the urban environment. 

Bringing green back for environmental and social cohesion

From constructed wetlands at the former London Olympic Park to urban farms in Singapore and Detroit, the range of responses developed by cities speaks to the benefits of tailored ecological approaches. In addition to environmental benefits, strategies such as urban agriculture offer social benefits, tackling food insecurity in areas of need and brining community members together.

In Washington DC, a series of nature-based solutions, including rain gardens, has been introduced to address both flooding and pollution caused by stormwater runoff flowing into the Chesapeake Bay. Financial incentives offered by the local government encouraged 4,000 homeowners to join the scheme, which currently runs a waitlist.

As we look to the work ahead for a net zero carbon future, nature-based solutions can serve as an effective tool to enrich our urban spaces environmentally, socially, and economically.

Authors: Hyon Rah (left, above), director in ESG Consultancy, US and Dr Kat Martindale (r), head of ESG research at Savills.