Nature Positive Cities Efforts to Advance the Transition San Francisco 2025

2 Assessment of enabling environment CASE STUDY 1 CASE STUDY 2 CASE STUDY 3 Managing natural habitats and ecosystems in support of net-zero carbon sequestration opportunities and trade-offs in the Alameda Watershed Challenge Ambitious net-zero greenhouse gas (GHG) emissions targets set by the state and local action plans pose significant challenges for San Francisco. To meet net-zero GHG emissions targets, decision-makers and land managers are looking to California’s open space – its forests, grasslands, shrublands and wetlands – to help reduce GHG emissions and draw down atmospheric carbon dioxide (CO 2). Protecting carbon stocks and increasing carbon sequestration can support climate change mitigation and maintain healthy, resilient ecosystems. To support city land managers in making informed carbon management decisions, the Alameda Watershed Carbon Assessment offers scientific guidance on the watershed’s current and potential performance as a natural climate solution. Solution The San Francisco Public Utilities Commission (SFPUC) and the San Francisco Estuary Institute conducted an analysis of the current and future carbon sequestration potential of the Alameda watershed lands (40,000 acres of land owned by the county). 24 This assessment was framed by two main objectives: to quantify current carbon stocks in the Alameda Watershed and to evaluate opportunities to enhance carbon sequestration in its vegetation and soils. The study provided insight into the relative carbon sequestration potential of different ecosystem types, and the extent to which the city can rely on carbon sequestration to achieve net zero by 2040. Analysis of the current levels of carbon storage highlighted six potential carbon management strategies to be used across the watershed that may be applicable to other open spaces in the state. Impact The watershed stores 2.5 million tonnes of carbon within its ecosystems (as of 2022). The riparian forests and oak woodlands in the watershed store as much carbon per acre as the Amazon rainforest, with 80% of the carbon being stored in soil organic matter. 25 A central tenet of this analysis is that the value of any management action depends on the ecological context. While the analysis demonstrated that the six potential strategies can increase carbon sequestration and restore biodiversity, an important finding was that open space preservation, i.e. simply keeping wild open spaces whole and healthy, is the most effective strategy. The study played a key role in San Francisco’s assessment of the potential for and limits of carbon sequestration in achieving the city’s GHG reduction goals. The most important conclusion from the analysis was that even with an “all-in” approach that implements all carbon farming strategies, regardless of co-liabilities and economics, the maximum annual carbon sequestration would equal 0.4% of San Francisco’s 1990 GHG emissions. While the city’s lands are critically important for local and regional biodiversity, they cannot be relied upon significantly for a carbon sequestration strategy relative to the city’s emissions reduction targets. Source: San Francisco Public Utilities Commission. (n.d.). Regional Watersheds. https://www.sfpuc.gov/about-us/our-systems/regional-watersheds. 32 Nature Positive: Cities’ Efforts to Advance the Transition