Final Report for Sea-level Rise Response Modeling for San Francisco Bay Estuary Tidal Marshes

Coastal ecosystems have been identified by the International Panel on Climate Change (2007) as areas that will be disproportionally affected by climate change. Recent sea-level rise projections range from 0.57 to 1.1 m (Jevrejeva et al. 2012) or 0.75 to 1.9 m by Grinsted et al. (2010) and Vermeer and Rahmstorf (2009) by 2100, which are contingent upon the ambient temperature conditions and CO2 emissions. Sea-level rise projections for San Francisco Bay are 1.24 m by 2100 (Cayan et al. 2008). The expected accelerated rate of sea-level rise through the 21st century will put many coastal ecosystems at risk, especially those in topographically low-gradient areas.
Sea-level rise response modeling was conducted at 12 tidal salt marshes around San Francisco Bay estuary where marsh accretion and plant community state changes were assessed to 2100. Detailed ground elevation, vegetation, accretion, and water level data were collected at all sites between 2008 and 2011 and used as model inputs. A modification of the Callaway et al. (1996) model, the Wetland Accretion Rate Model for Ecosystem Resilience (WARMER), was developed to run sea-level rise response models for all sites (Swanson et al. submitted). Our results showed that the vast majority, 95.8% (1,942 ha), of the marshes in our study were projected to lose marsh plant communities by 2100 and transition to mudflats. Three marshes were projected to maintain marsh vegetation to 2100, but they only comprised 4.2% (85 ha) of the total marsh area surveyed.