Working with nature within and around cities can protect vulnerable urban residents from climate change impacts and disasters, improve their quality of life, and reduce the impacts of cities on other valuable systems, argues Dr Hannah Reid.
A Central Role in Adaptation
The value of nature-based solutions (NbS) and ecosystem-based adaptation (EbA) in the urban context is increasingly acknowledged. The Durban Adaptation Charter prioritises the role of functioning ecosystems as core municipal green infrastructure and recognises that sustainable management, conservation, and restoration of ecosystems and related ecosystem services are central to adaptation.
The Global Research and Action Agenda on Cities and Climate Change Science stresses the need for further research and action on EbA and on green alternatives to dominant grey infrastructure approaches to addressing climate change in rapidly developing urban areas. The UN-endorsed New Urban Agenda includes environmental sustainability and the protection of ecosystems and biodiversity as one of its three transformative commitments.
Traditionally, however, biodiversity within and around cities has often been destroyed and under-valued. Some perceive NbS as competing with urban development needs. Such perception is misleading, as the destruction of waterways, forests, mangroves, open spaces, and vegetated hillsides and coastlines reduces people’s ability to deal with climate impacts and thus hinders sustainable urban development.
For example, building on floodplains and wetlands has reduced natural drainage areas. Vital resources and ecosystem services, such as water and food, also come from areas outside urban centres, so urban adaptation cannot be considered in isolation from surrounding rural areas.
Nature’s Potential for the Urban Poor
NbS hold a lot of potential for adaptation benefits that are especially important for the urban poor. They are particularly vulnerable to a variety of risks: flood risks, in part because they often live in risky locations such as low-lying coastal areas or floodplains, have less access to drainage infrastructure and secure clean water supplies. They are also less able to control the temperatures of where they live and work. Generally, the adaptive capacity of poor people – in cities as well as rural areas – is more dependent on natural resources and the sustainable provision of ecosystem goods and services.
Natural solutions can complement or replace ‘hard infrastructure’ to support adaptation for the urban poor in various ways:
- Regulating city air temperatures. Heat stress is a major urban health issue. Global temperature increases of 1.3 to 1.8˚C are expected by 2100, but the urban heat island effect means urban air temperatures are on average 2 to 5˚C higher, and sometimes more than 10˚C higher, than outside cities. Tree cover, green roofs or walls, wetlands, and natural water reservoirs can help address this problem, reducing urban temperatures by up to 10°C. Green roofs can also provide insulation in winter.
- Managing storm water and flooding. In urban areas, impervious surfaces mean rainfall is quickly converted to surface runoff which can overwhelm drainage systems and cause flooding. Green roofs, parks and permeable pavements, tree planting and wetlands can complement storm water infrastructure, such as drains, by reducing surface runoff and increasing infiltration into soils and groundwater. For example, Bioswales – vegetated channels that convey storm water – can reduce peak flows by 89 per cent.
- Improving urban water supplies. Integrated watershed management and forest restoration in areas around urban areas can help regulate and improve the quality and sustainable delivery of urban water supplies. Protecting floodplains can recharge groundwater supplies and community gardens can increase soil water retention.
- Protecting urban coastlines. In coastal cities, reefs, wetlands, and mangroves provide natural defences against climate change induced rising sea levels, storm surges, and coastal erosion. Coral reefs and salt marshes are particularly effective at reducing wave heights.
- Reducing wind erosion. Vegetation can act as a barrier to wind, thus protecting against desertification.
The Co-Benefits of Investing in Nature
Multiple broader social and environmental benefits follow investments in nature. These contribute to a range of international development and environmental commitments, notably under the Sustainable Development Goals and the UNFCCC Paris Climate Change agreement. This is especially true for poor and vulnerable people – such as women – who depend more on ecosystem services for their livelihoods.
- Routes out of poverty. Coastal mangroves can provide poor communities with timber, fish, and honey; urban agriculture can increase income for poor households.
- Health benefits and food security from a greater variety in food sources, and better nutrition, for example from urban gardens.
- Reduced pollution and better urban water drainage and treatment. Green urban infrastructure can improve the quality of urban waste water and thus reduce the contamination of marine environments, rivers, and the water sources depended upon by urban residents. Unlike grey infrastructure, bioswales and wetlands for managing storm water and flooding can trap pollutants, nutrients, microbial contaminants, and sediments. Green infrastructure such as greenbelts can also reduce particulate air pollution.
- Amenity benefits. Parks and tree planting in cities improve scenery and provides recreation opportunities which can lead to a multitude of physical, well-being, and mental health benefits.
- Climate change mitigation. Natural infrastructure both sequesters carbon and reduces the need for carbon-intensive concrete infrastructure.
- Potential for citizen’s involvement in governance and monitoring, facilitating social cohesion and social justice for the urban poor. This can help ameliorate the potential costs and trade-offs associated with EbA, such as ‘green gentrification’.
Is Investing in Nature Economically Viable?
Evidence regarding the financial viability of investing in nature-based solutions for adaptation in urban areas is growing. Project level investments can offer high rates of return. For example, engineered solutions for flood mitigation and storm surge protection in Lami town, Fiji, generally provided less than half the benefit / cost ratio of EbA solutions.
Using nature can complement engineered solutions, and in many instances, hybrid ‘green-grey’ infrastructure solutions may work best. For example, every dollar invested in EbA measures restoring urban waterbodies in Hue City, Vietnam, returned 34 dollars, and benefits were larger when EbA measures were combined with engineered measures – in this case sluice gates.
People in The Thi Nai Lagoon, Quy Nhon, Vietnam earned twice as much from mangrove restoration (introduced to buffer the impacts of rising sea levels and more intense and frequent storms), as from aquaculture. Such wider economic benefits to society from EbA, – through growth, exports, revenues, employment, improved income, avoided costs, reduced energy demand, and increased land value – can be hard to quantify. Yet, they are significant, emphasising the continued need to invest in EbA and NbS in order to ensure truly sustainable urban development.