Da Quake

Image: KQED

This morning’s magnitude 6.5 earthquake in the waters offshore of Eureka in northern California (technically 160 km west of Ferndale, California) and raft of emails we are getting in the wake of this news provide a convenient opportunity to reiterate that responsibly and effectively dealing with the threat of coastal flooding associated with sea level rise has many additional benefits, perhaps chief among them in the context of today’s discussion is improved protection from seaquake-induced tsunami flooding.

Just this week I lectured about the threat climate change poses to our coastal zone. While there are many threats to be sure, the threat that the general public can most readily identify, is the easiest to intuitively grasp, and is the simplest to quantitatively estimate is sea level rise (often abbreviated as simply SLR).

California’s Approach to Earthquakes

Earthquakes are a part of life for those of us here in California and across the Pacific Rim’s so-called Ring of Fire. Our initial (modern) response to quakes really got going in the wake of the devastating 1906 earthquake that rocked the San Francisco Bay Area. That tumbler destroyed much of San Francisco, turned a good chunk of Golden Gate Park into a homeless encampment for more than a year, and generally reset the table on a whole host of physical and social systems. Out of that came improved policies on disaster response, municipal water systems (if we consider almost destroying Yosemite Valley and actually destroying Hetch Hetchy Valley an “improvement”…but I digress), and (eventually, after several more quakes) building codes. Much of our planning for earthquakes over the ensuing decades emphasized requiring buildings to be constructed such that occupants would survive and be able to exit the building before the quake-induced collapse of the structure. More recently (since the early 1990s) we have shifted our emphasis to begin to require new building designs that make our structures not only survivable for people but survivable for the infrastructure/society as well. The idea here is that a resilient house is vastly more desirous than a house that will need to be condemned in a quake’s wake, costing the homeowner hundreds of thousands of dollars (or more) and years of dislocation.

Homeless encampment in San Francisco’s Presidio four days-post quake/fire. Image No. 44. Entitled “More military help – 4th day.” Image: Record Group 46, Records of the United States Senate, National Archives.

We need to take a similar approach to thinking about our coastal zone. Evolving our coastal zone such that higher and higher water does not necessitate idiotic and ultimately futile ocean walls/barriers that destroy our coastal ecosystems, culture, businesses, and society is what we need now.

This is the kind of lame management decision that we want to avoid. Hardened seawalls don’t typically solve a thing. They simply make the problem worse. Image: climatetechwiki.org

Sea Level Rise in California

Over the past century, sea level has risen nearly 20 cm (8 inches) along the California coast. The Intergovernmental Panel on Climate Change (IPCC) and various general circulation model scenarios strongly suggest quite significant increases in sea level elevation off across the state’s coastline due to climate change over the coming century.

Coastal Flooding Risks

Something in the neighborhood of 40% of the residents in the continental United States reside near our coastlines. These areas in turn are home to both most of our nation’s economic activity and our greatest population growth rates. Add in the low elevations of our coastal fringes in this era of rising seas and we get increasing long-term exposure risk for to flooding. Hauer and Evans (2015) estimate that we are talking about something like 1.3 million, 3.4 million, and 11.7 million people in the continental United States at risk of inundation-related displacement under scenarios of 0.3 m, 0.9 m, and 1.8 m sea level rise by 2100. Hauer and Evans note that:

The magnitude of populations displaced from sea level rise could mirror the Great Migration of southern African-Americans during the 20th century and radically alter the future distribution of the US population. It could cost up to $US11.7 trillion to relocate these displaced populations, based on costs associated with managed retreats [from the IPCC].

San Francisco International Airport in 1946 as it began its displacement of salt marsh around the edge of San Francisco Bay. Image: Aerial Archives

Setting the people part aside, our coastal infrastructure itself is amazingly vulnerable. We have loved putting our powerplants in coastal estuaries, our airports in bays, and our economic engines just a few centimeters or meters above mean high tide. The best report on our vulnerablility in California to date has come from a 2009 study by the Pacific Institute which only used existing human populations (i.e. assumed no population growth). That reported noted:

We estimate that a 1.4 meter sea level rise will put 480,000 people at risk of a 100‐year flood event, given today’s population. Among those affected are large numbers of low‐income people and communities of color, which are especially vulnerable. Critical infrastructure, such as roads, hospitals, schools, emergency facilities, wastewater treatment plants, power plants, and more will also be at increased risk of inundation, as are vast areas of wetlands and other natural ecosystems. In addition, the cost of replacing property at risk of coastal flooding under this sea level rise scenario is estimated to be nearly $100 billion (in year 2000 dollars). A number of structural and non‐structural policies and actions could be implemented to reduce these risks. For example, we estimate that protecting some vulnerable areas from flooding by building seawalls and levees will cost at least $14 billion (in year 2000 dollars), with added maintenance costs of another $1.4 billion per year. Continued development in vulnerable areas will put additional areas at risk and raise protection costs.

Large sections of the Pacific coast are not vulnerable to flooding, but are highly susceptible to erosion. We estimate that a 1.4 meter sea‐level rise will accelerate erosion, resulting in a loss of 41 square miles (over 26,000 acres) of California’s coast by 2100. A total of 14,000 people currently live in the area at risk of future erosion. Additionally, significant transportation‐ related infrastructure and property are vulnerable to erosion. Statewide flood risk exceeds erosion risk, but in some counties and localities, coastal erosion poses a greater risk. This report also provides a comprehensive set of recommendations and strategies for adapting to sea‐level rise.

Southern California power plants vulnerable to a 100-year coastal flood with a 1.4 meter sea-level rise. Map: Pacific Institute.

See for yourself

A few years back we needed to rely on professors like me (or more accurately our undergraduate researcher assistants who would do most of the work) to generate maps and graphics of inundation. No longer! We are blessed now with a host of various online viewers where anyone with a web browser can explore the potential flooding associated with sea level rise.

Some of these are simple “bathtub” models wherein we take the elevation of the land and draw polygons at a constant elevation to show the areas at risk. This is essentially looking at a topographic model of our coast. A great example of this would be NOAA’s Sea Level Rise Viewer:

A newer suite of sea level rise viewers tries to go beyond that simple “bathtub” approach, overlaying additional dynamics into the predictions. A great example of this category of predictors is The Nature Conservancy’s modeling effort here in Ventura County. For this viewer we added in the changing impact of long-term exposure to higher water levels, erosion, conversion of various vegetation communities, saltier water intrusions, etc. Check out TNC’s Coastal Resilience Viewer here:

All of these sea level rise visualizations are also are great “first pass” estimates of tsunami vulnerability as well.


In this era where much is being made about limited political collaboration and deep philosophical divisions between various camps in our divided nation, infrastructure investment may be be one hopeful area of agreement. Here is hoping that this quake off the coast of California can remind us that ecologically responsible coastal infrastructure improvements could pay dividends for decades to come.

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