Sea level rise is coming, and its impacts will be far reaching. For the state of California, the threat of sea level rise may prove existential. More than two-thirds of its population lives in the states’ 21 coastal counties, which are responsible for 85 percent of the state’s GDP.
However, sea level rise will not just impact human activity. Rising tides will also drastically alter, and in some cases destroy, important coastal habitats. Conserving California’s Coastal Habitats, a new report from The Nature Conservancy, provides a startling analysis of the future of California’s coast and charts a path forward for coastal conservation efforts.
The California coast represents the most biodiverse region in the country’s most biodiverse state, lending nationwide significance to coastal conservation efforts there. “The state of California has been a leader in environmental policy for over a century,” say the report’s authors, praising the state’s “legacy of coastal conservation.”
“However, current policy and decision-making frameworks were developed to reflect static existing conditions and are not well suited for the dynamic needs of adapting to sea level rise,” the authors warn.
At risk are “nesting areas along global migrations for diversity of species, as well as nesting and pupping habitat, nursery habitat, and important feeding grounds critical to populations of many species, some which are found nowhere else in the world.”
Sea level rise threatens areas of human settlement and activity, too. The conversion of land to tidal and subtidal coastline will reduce the size of natural buffers, providing less protection to human settlements in coastal flooding events. Saltwater intrusion will impact agriculture. According to the authors, “sea level rise and associated flooding will threaten nearly $100 billion worth of property along the California coast by 2100.”
The report’s authors used GIS to identify and map the coastal habitats, ecosystems, and infrastructure most at risk from sea level rise. They based their projections on two and five feet of sea level rise, which they say are in keeping with projections issued by the California Coastal Commission. The authors then developed metrics to measure the potential impact of sea level rise on a given area and the area’s vulnerability and ability to adapt.
Their findings are worrying. “As much as 25 percent of the existing public conservation lands within the analytic zone will be lost to subtidal waters,” they warn. Habitats for eight imperiled species will be completely inundated. Large portions of other significant coastal habitats are “highly vulnerable,” including 58 percent of rocky intertidal habitats, 60 percent of upper beaches, and 58 percent of regularly-flooded estuarine marshes. “At least half of the documented haul-outs for Pacific harbor seals and Northern elephant seals, and nesting habitats for focal shorebirds like black oystercatchers, are also highly vulnerable.”
The report’s maps show that habitats in the San Francisco Bay Area are particularly at risk. There, vulnerable landscapes and habitats–such as 87 percent of the state’s regularly-flooded estuarine marsh–will be trapped between rising seas on one side and human development on the other. “The built environment–including roads and other infrastructure–creates barriers that prevent coastal habitats from moving inland,” while “dikes, levees, and other water control features negatively impact the health and function” of these threatened landscapes.
The authors found that sea level rise could adversely affect public access to California’s coast. “Sea level rise will diminish coastal access opportunities throughout the state by reducing beach widths, submerging rocky intertidal areas, and flooding coastal beach infrastructure.”
In the face of these potentially-devastating impacts, the report’s authors present a suite of strategies for conservation in the era of climate change. According to the authors, conservation managers need to “conserve and manage for resilience.” This includes maintaining the conservation status of existing conserved lands and identifying and protecting resilient coastal landscapes that are not vulnerable to sea level rise.
The Nature Conservancy recommends managing for resilience through the use of sediment augmentation and sand placement. “The majority of highly vulnerable conservation lands in need of managing in place for resilience are found in the San Francisco Bay Delta,” an observation that speaks to the importance of landscape-led initiatives such as the recent Resilient by Design Bay Area Challenge.
The authors also call for conserving nearly 200 square kilometers of potential future habitat areas and adapting the built environment “with more natural coastal processes in mind” – in effect, giving the coastline room to change.
“As sea levels rise, California’s coast will erode and evolve, and habitats will need to shift. Our current conservation efforts and land use management decisions must focus on further supporting these natural processes and enabling the transition and movement of coastal habitats as sea levels rise. Conservation in the face of sea level rise requires an adaptive process that embraces the reality of a dynamic coastline.”
The reports’ recommendations and strategies are “spatially explicit,” with specific recommendations for areas depending on their vulnerability and adaptive capacity. There are detailed high-resolution maps that illustrate the location, distribution, and severity of risks as well as opportunities.
“The results of this spatially explicit assessment provide a foundation of information to support immediate action to conserve habitats and biodiversity in the face of sea level rise,” the authors argue. “With so much of California’s coastal habitats, imperiled species, and managed lands at risk from sea level rise, immediate collective action is necessary to conserve these natural resources into the future.”