It is estimated that two out of every three people will live in cities by 2050. As the world becomes increasingly urbanized, cities face the challenge of growing and developing while providing a healthy, safe, equitable and sustainable living environment for their residents. For many cities, this is especially challenging due to the increasing frequency and severity of climate change-related hazards such as extreme weather events and sea level rise. More and more, city leaders are looking for efficient, low-cost solutions that reduce the impact of these hazards and deliver multiple benefits to improve the resilience and livability of urban areas. To this end, nature-based solutions, often in the form of “green infrastructure”, may provide critical ecosystem services that improve air and water quality, mitigate flooding and extreme temperatures, and enhance health and well-being. However, the value of urban ecosystem services often remains uncertain, as it varies greatly with the specific characteristics of a city or neighborhood. To better understand this variation and help decision-makers assess the suitability of nature-based solutions for their city, we reviewed research on ten urban ecosystem services and identified the contextual factors, co-benefits, trade-offs and equity implications that influence the value of nature in cities.
Results/Conclusions
We found that the value of urban ecosystem services depends on a multitude of social, ecological, and technical factors, such as household income, climate, and quality of existing built infrastructure. Beyond these contextual factors, nature’s value in cities is also influenced by the co-benefits it can provide, and the trade-offs that must be considered. For example, street trees may improve air quality, but they can also regulate temperatures, supply shade, retain stormwater, sequester CO2, and provide aesthetic benefits. On the other hand, they often require maintenance and irrigation, and can produce leaf litter and allergens. We also outline cases in which alternative interventions may be more cost-effective than nature-based solutions. Most importantly, we highlight the importance of comprehensively assessing the distribution of benefits and costs associated with nature-based solutions to ensure equitable outcomes and the protection of vulnerable urban populations. We synthesize these insights and identify strategies to more efficiently, effectively, and equitably implement nature-based solutions with the goal of enhancing sustainability, human well-being, and resilience to extreme events in cities across the world.