Feasibility of Afforestation as an Equitable Nature-Based Solution in Urban Areas

Although nature-based solutions for urban heat mitigation have gained momentum, it is important to quantitatively assess the feasibility of such strategies to utilize space efficiently and prioritize lower-income communities, who have fewer options for climate change adaptation. Here we combine data from US census estimates, satellites, and satellite-derived products to develop a framework to target potentially suitable areas for urban afforestation to mitigate urban heat and minimize tree cover disparity. We test this framework for California, the most populated state in the US and the 5th largest economy (by GDP) in the world, and show that space exists for an additional 34 million (1.2 million acres of) trees in the state’s urban areas. This would reduce the average urban land surface temperature (LST) by 1.7 °C and provide multiple co-benefits totaling $1.1 billion annually, including reduction in heat-related medical visits (>3000 over 10 years) and 3.9 million metric tons of annual CO2 sequestration. Without any intervention to reduce urban LST, the net present value of the social cost of carbon from residential electricity use ranges from $12.9 million to $102.1 million. Because funding is limited, we provide suitability scores for urban afforestation at the census block group (CBG) scale based on multiple considerations. In California for instance, equitable urban afforestation in CBGs with positive suitability scores will serve 89% of the ≈9 million urban residents in the lowest income quartile for their cities. This method can guide equitable urban afforestation efforts and can be scaled to other North American cities.