Projected Loss of Western Snowy Plover Critical Habitat in the San Francisco Bay Area Due to Sea Level Rise

Source: Monterey Bay Aquarium

Climate change is expected to impact a wide range of species across a variety of ecosystems and geographies. Coastal ecosystems may face the most devastating alterations, as sea level rise (SLR) caused by accelerated melting of land-ice and thermal expansion of the oceans is expected to rapidly transform coastlines. At this point, SLR of at least 3 ft seems certain by the end of the 21st century¹.

The western snowy plover (WSP; Charadrius nivosus nivosus), a small shorebird found in the western and southern United States, as well as parts of South America and the Caribbean, may be one of the first species to feel the effects of sea level rise. The WSP nests just above the high tide line on sandy beaches, vegetated dunes, and on levees and salt pond flats from March through September². Current challenges facing the WSP include low reproductive success, loss of nesting habitat due to human disturbance and invasive species, predation, and severe weather³. So sensitive is the WSP that even something as simple as a kite flying over the nest may prompt a mother to abandon its young for fear of predators⁴. While the global WSP population is listed as Near Threatened by the IUCN, the Pacific population, which spans from the coast of Washington to Baja California, has been listed as federally threatened by the US Fish and Wildlife Service (USFWS) since 1993³.

SLR may exacerbate conservation concerns for the WSP by reducing, fragmenting, and, in some cases, completely inundating critical nesting habitat. Identifying vulnerable areas and prioritizing habitat for protection can help managers get ahead of the crisis. However, understanding where and when habitat will be impacted is not so simple, as coastal geography and the level of human development influence how habitat will be inundated and whether there is an upland buffer area for the birds to retreat. In order to begin addressing this knowledge gap, I seek to model critical habitat loss in the San Francisco Bay Area under a scenario of SLR of 3 ft.

I use Carto to develop simple web maps depicting the extent of critical habitat impacted by 3 ft of SLR at each location in the San Francisco Bay Area. The WSP critical habitat data is taken from the USFWS, as revised in 2011. Critical habitat is a term defined by the Endangered Species Act (ESA) as an area that contains features essential for the conservation of a threatened or endangered species and that may require special management and protection. Critical habitat may include an area that is not currently occupied by the species but that will be needed for its recovery. The sea level rise data is taken from the National Oceanic and Atmospheric Administration (NOAA), and depicts mean sea level rise of 3 ft above current Mean Higher High Water (MHHW) level, which represents the highest expected tide level at a given location. This measure of sea level rise is appropriate for delineating impacts on WSP nesting habitat, since the WSP typically nests just above the high tide line.

Since most WSP critical habitat is found within Marin, Napa, Alameda, and San Mateo Counties in the Bay Area, I split up my analyses by county (Figure 1) — beginning with Marin (Figure 2).

Figure 1. Study Area: San Francisco Bay Area, CA, including Marin, Napa, Alameda, and San Mateo Counties

Figure 2. Current Extent of Western Snowy Plover Habitat in Marin County, CA
#Figure 2 (above) was generated by overlaying layers of Marin County and WSP Critical Habitat. Marin County was derived from a larger dataset featuring all US counties based on its FIPS code using the following SQL query:
SELECT * FROM cb_2013_us_county_500k
WHERE countyfp = '041' AND statefp = '06'
#Another column, 'county_name' was added to the dataset in order to include the name "Marin County" as a label. The layer color and transparency were adjusted for appearance.

In Marin County, WSP critical habitat primarily occurs along beaches in Point Reyes National Seashore (PRNS). These areas appear to have a more significant elevational gradient than other habitat areas in the Bay Area, as no habitat is entirely lost in response to the given scenario of SLR (Figure 3). However, much of the habitat is diminished and disjointed, especially at Limantour Beach, where 71.37% of critical habitat is lost (Figure 4). Critical habitat at Abbotts Lagoon holds strong in the face of the 3 ft SLR, but habitat at Kehoe Beach just to the north is largely reduced, with a total of 41.31% of critical habitat being lost along the western beaches of PRNS. Just north of PRNS, across the entrance to Tomales Bay, critical habitat at Dillon Beach is reduced by 54.50%.

#Western Snowy Plover (WSP) critical habitat lost due to a scenario of 3 ft sea level rise (SLR) was determined by clipping the current habitat extent layer to the 3 ft SLR layer, using the following SQL query:
SELECT wsp_2011.unit_name, ST_INTERSECTION(wsp_2011.the_geom_webmercator, slr_3ft.the_geom_webmercator) as the_geom_webmercator
FROM wsp_2011, slr_3ft
WHERE ST_INTERSECTS(wsp_2011.the_geom_webmercator, slr_3ft.the_geom_webmercator)
Figure 3. WSP critical habitat loss due to 3 ft of SLR at Point Reyes Beach (North and South) and Limantour Beach, Point Reyes National Seashore, Marin County
#The proportion of habitat inundated by 3 ft SLR was calculated usinng the following sequence of SQL queries:
#Calculate area inundated
SELECT unit_name, SUM(area) as area_inundated
FROM (
SELECT
wsp_2011.unit_name,
slr_3ft.*,
ST_Area(
ST_Intersection(
wsp_2011.the_geom_webmercator,
slr_3ft.the_geom_webmercator
)
) AS area
FROM
wsp_2011, slr_3ft
WHERE
ST_Intersects(
wsp_2011.the_geom_webmercator,
slr_3ft.the_geom_webmercator
)
) AS mytable
GROUP BY unit_name
#Calculate current habitat area
SELECT unit_name, ST_Area(the_geom_webmercator) as current_area
FROM wsp_2011
#Calculate proportion
SELECT unit_name, area_inundated / current_area as proportion
FROM
(SELECT area_sqm.*, wsp_2011_st_area.st_area
FROM wsp_2011_st_area
INNER JOIN area_sqm
ON wsp_2011_st_area.unit_name=area_sqm.unit_name) as mytable
Figure 4. WSP critical habitat loss due to 3 ft of SLR at Limantour Beach, Point Reyes National Seashore, Marin County
Figure 5. WSP critical habitat loss due to 3 ft of SLR at Abbotts Lagoon and Kehoe Beaches, Point Reyes National Seashore, Marin County
Figure 6. WSP critical habitat loss due to 3 ft of SLR at Dillon Beach, Marin County

Figure 7. Current Extent of Western Snowy Plover Habitat in Napa County, CA

WSP critical habitat only occurs at one isolated location in Napa County (Figure 7) — at Napa Slough near the confluence of Napa River and San Pablo Bay. Under the scenario of 3 ft SLR, 99.70% of critical habitat at Napa Slough is lost (Figure 8). Although the elevational gradient appears limited, the surrounding areas are less developed than other parts of the bay, and the WSP could potentially adjust its habitat setting at Napa Slough to accommodate the change in sea level.

#Figure 7(above) was generated by overlaying layers of Napa County and WSP Critical Habitat. Napa County was derived from a larger dataset featuring all US counties based on its FIPS code using the following SQL query:
SELECT * FROM cb_2013_us_county_500k
WHERE countyfp = '055' AND statefp = '06'
#Another column, 'county_name' was added to the dataset in order to include the name "Napa County" as a label. The layer color and transparency were adjusted for appearance.
Figure 8. WSP critical habitat loss due to 3 ft of SLR at Napa Slough / Coon Island, Napa County, CA

Figure 9. Current Extent of Western Snowy Plover Habitat in Alameda County, CA
#Figure 9 (above) was generated by overlaying layers of Alameda County and WSP Critical Habitat. Alameda County was derived from a larger dataset featuring all US counties based on its FIPS code using the following SQL query:
SELECT * FROM cb_2013_us_county_500k
WHERE countyfp = '001' AND statefp = '06'
#Another column, 'county_name' was added to the dataset in order to include the name "Alameda County" as a label (Note that three labels appear because the county is divided into three separate congressional districts). The layer color and transparency were adjusted for appearance.

In Alameda County, WSP critical habitat occurs at Eden Landing Ecological Reserve and at Don Edwards National Wildlife Refuge in the Baylands district of Fremont, CA. In both cases, the habitat exists as marshland and salt pond flats with a highly restricted elevational gradient. Under the given scenario of SLR, 99.12% of habitat is inundated at Eden Landing (Figure 10) and 99.28% at Baylands (Figure 11). This is especially concerning here, because the highly developed upland areas leave little room for the birds to retreat in response to SLR. Most likely, the WSP will no longer be able to nest within San Francisco Bay.

Figure 10. WSP critical habitat loss due to 3 ft of SLR at Eden Landing Ecological Reserve, Alameda County
Figure 11. WSP critical habitat loss due to 3 ft of SLR at Don Edwards San Francisco Bay National Wildlife Refuge, Baylands, Fremont, Alameda County, CA

Figure 12. Current Extent of Western Snowy Plover Habitat in San Mateo County, CA
#Figure 12 (above) was generated by overlaying layers of San Mateo County and WSP Critical Habitat. San Mateo County was derived from a larger dataset featuring all US counties based on its FIPS code using the following SQL query:
SELECT * FROM cb_2013_us_county_500k
WHERE countyfp = '081' AND statefp = '06'
#Another column, 'county_name' was added to the dataset in order to include the name "San Mateo County" as a label. The layer color and transparency were adjusted for appearance.

In San Mateo County, WSP critical habitat only exists at Ravenswood Pond SF2, part of Don Edwards National Wildlife Refuge near the southwest end of the Dumbarton Bridge. Under the given scenario of SLR, 100% of the habitat is consumed at Ravenswood Pond SF2 (Figure13). This large salt pond flat is bordered by roads and housing development, making upland retreat of WSP nesting grounds unlikely.

Figure 13. WSP critical habitat loss due to 3 ft of SLR at Ravenswood Pond SF2, Don Edwards San Francisco Bay National Wildlife Refuge, Menlo Park, San Mateo County, CA

Results of my analyses suggest that WSP critical habitat will be significantly reduced by the end of the 21st century. The birds may be unable to adapt in areas with minimal elevational gradients and significant upland development. Land managers must consider these forecasted challenges when developing conservation strategies. Modeling gradated transformations in habitat in response to different scenarios of SLR could provide a higher-resolution view of the timeline and manner of change. Novel approaches to restoring existing habitat or creating new habitat will be needed to combat the impacts of SLR.


References:

¹NASA Science Zeros in on Ocean Rise: How Much? How Soon?, RELEASE 15–174. 2015. http://www.nasa.gov/press-release/nasa-science-zeros-in-on-ocean-rise-how-much-how-soon.

²The Cornell Lab of Ornithology, All about Birds, Internet URL: https://www.allaboutbirds.org/guide/Snowy_Plover/id, accessed March 2016.

³US Fish and Wildlife Service, Internet URL: www.fws.gov/arcata/es/birds/WSP/plover.html, accessed March 2016.

⁴Western Snowy Plover, Internet URL: http://www.westernsnowyplover.org/, accessed March 2016.

Data Sources:

Sea Level Rise Data:

WSP Critical Habitat (2011) Data: