About The Maps

Recommended citation for the web application

Veloz, S., M. Fitzgibbon, D. Stralberg, S. Michaile, D. Jongsomjit, D. Moody, N. Nur, L. Salas, J. Wood, M. Elrod, and G. Ballard. 2014. Future San Francisco Bay Tidal Marshes: A climate-smart planning tool. [web application]. Petaluma, California. (www.pointblue.org/sfbayslr).

Tidal marsh elevation models

Understanding San Francisco Bay’s vulnerabilities to sea level rise is important for both biodiversity conservation and for management of public infrastructure. Coastal marshes provide essential ecosystem services such as water filtration and flood abatement while also providing important habitat for species of conservation concern. Improving our understanding of how tidal marsh habitats will be affected by sea level rise is important so that we maximize ecosystem services that coastal marshes provide and ensure that endemic populations of plants and animals persist into the future.

For this project, marsh accretion was modeled by ESA PWA using the Marsh-98 model (Orr et al. 2003) and described here. The model assumes that rates of marsh plain elevation change depend on the availability of suspended sediment and organic material, water depth, and duration of inundation periods. If enough suspended sediment is available, then tidal marsh elevations can keep pace with increased inundation.

Model outputs were linearly interpolated in 10-cm increments for starting elevations ranging from -3.7 to 1.7 m (relative to mean higher high water, or MHHW), and applied to a composite 5-m elevation grid (see below) for SF Bay. Results for each possible combination of projected sea level rise, sediment and organic material availability, and target year were combined to produce the scenario layers.

Species distribution modeling

Maps of the distribution of tidal marsh bird species were modeled using boosted regression trees (Elith et al. 2008)and described by Veloz et al. (2011). This method is able to fit non-linear functions between environmental variables and the presence/absence of a species. Map values represent the predicted density (birds per hectare) of a species.

By analyzing changes in species distributions under the different future tidal marsh elevation scenarios we can test how sensitive species are to future climate change and estimate the uncertainty in species responses to our future scenarios.

About The Data

Elevation modeling

The digital elevation model (DEM) was developed by The USGS Earth Resources Observation and Science (EROS) Data Center and based on recently collected multibeam bathymetry data and topographic Light Detection and Ranging (LiDAR) remote sensing data (http://viewer.nationalmap.gov/viewer/). Elevations at locations within Suisun Bay were field sampled with GPS data to investigate systematic bias in the data. In some areas, errors due to impenetrable mats of vegetation caused erroneously high elevations. Where possible, vegetation data was used to develop correction factors for these errors then applied to the elevation layer. All datasets were converted to the NAVD88 vertical datum and resampled to a 5 meter resolution. The NAVD88 vertical datum of the elevation data was converted to MHHW reference levels using NOAA tidal gauge and benchmark data. Our models are designed to easily incorporate more accurate elevation data as it becomes available.

Rates of sea level rise were based on two non-linear scenarios provided by the US Army Corps of Engineers (2009) from curves provided by the National Research Council to project moderate and high sea level rise over the next century (0.52m and 1.65m). Different input parameter values for sediment supply and organic accumulation were given to 15 geographic sub-regions within the bay to account for the regional variability in these values. Each subregion was assigned a high and low value for sediment supply and organic accumulation based on a combination of USGS monitoring reports, observed accretion rates from restored sites, and expert opinion. For future scenarios, six different suspended sediment concentrations were modeled: 25, 50, 100, 150, 200, 250 and 300 mg/L. Three rates of organic matter accumulation were modeled: 1, 2 and 3 mm/yr, encompassing the presumed range of variability within San Francisco Bay including Suisun Bay (see Figure 1 below).

"Diked areas" are areas that are currently restricted from tidal inundation by dikes, levees or roads. A composite diked areas layer was developed based on the San Francisco Estuary Institute's EcoAtlas (http://www.sfei.org/ecoatlas)modern baylands layer, a levee layer developed for the Pacific Institute's sea level rise impacts study (http://www.pacinst.org/reports/sea_level_rise/data/index.htm)and inspection of aerial photography from Google Maps and the Natural Resource Conservation Service.

The urbanization layer was obtained from the NOAA coastal change analysis program (NOAA C-CAP) and is used to identify areas of current and future residential development.