Modeling Sea-Level Rise in San Francisco Bay Estuary

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RISING CONCERNS

Anthropogenic climate change is projected to result in at least a 2°C increase in global mean temperature by 2100 (IPCC 2007). Coastal ecosystems, including salt marshes, will be impacted by climate change through accelerating sea-level rise (SLR, Holgate and Woodworth 2004, Kemp et al. 2011), shifting precipitation patterns (Hamlet and Lettenmaier 2007, Bengtsson et al. 2009), and changing frequency and intensity of storms (Emanuel 2005, Webster et al. 2005, IPCC 2007, Cayan et al. 2008). Global sea-level rise (SLR) projections range from 1.0 to 1.9m by 2100 (IPCC 2007; Jevrejeva et al. 2010; Vermeer and Rahmstrof 2009), which will result in the loss of salt marshes and their associated wildlife species.  Melting continental ice at the poles, retreating glaciers, and the thermal expansion of the ocean all contribute to SLR.

It is the aim of our program to provide site specific sea-level rise predictions to land managers through the intensive collection of field data and innovative predictive modeling.  In 2009 and 2010, thousands of elevation and vegetation survey points were collected in salt marsh at 12 sites surrounding San Francisco Bay. The elevation data was synthesized into a continuous elevation model for each site, providing land owners valuable baseline data. 

A new marsh accretion model, WARMER, (Swanson et al., submitted) was developed to assess the risk of sea-level rise to salt marsh parcels around San Francisco Bay.  Additional sediment data was collected at four representative sites to provide inputs for the WARMER model.  The results of WARMER were then extrapolated to the remaining study sites.  WARMER indicates that most salt marsh around San Francisco Bay will transition from high to mid marsh by 2040, to low marsh by 2060 and to mudflat by 2080, however there is a great deal of variation around the bay.  The rate of sea-level rise and local accretion rates may be very different than the parameters used for the model, thus WARMER results are best characterized as one possible scenario of how the salt marsh platform may respond to rising sea-levels.

www.werc.usgs.gov/SFBaySLR