14.13: It’s Not Just Sea Level Rise

Unfortunately, sea level rise—even when accounting for vertical land motion—isn’t the only factor to affect flooding of coastlines. Short-term events lead to temporary and extreme sea level rise. Factors that cause rapid sea level rise include climate cycles (e.g., El Niño), tidal cycles (e.g., king tides), storm surges (e.g., hurricanes), and large ocean waves (e.g., storm swell). Each of these factors may add additional and significant increases to sea level over timescales from days to months and longer. If they overlap—for example, if a king tide coincides with the arrival of storm surge and wave swell from a hurricane—significant damage is a greater possibilty.

Sea level rise has already contributed to the phenomenon known as nuisance flooding—a (usually) tidally driven rise in sea level that causes seawater to inundate coastal areas. NOAA defines nuisance flooding as water levels that exceed the mean high high water by 1.6 to 2.1 feet (0.5–0.65 m; e.g., Sweet et al. 2020). Though considered minor in terms of harm to citizens or damage to properties, nuisance flooding can disrupt daily activities, damage property and infrastructure, and threaten human health (Mofktakhari et al. 2018). In Miami, Florida—which has become a kind of poster child for nuisance flooding—city streets and sidewalks become impassable, parking garages and landscapes flood, and septic systems leak into the streets during king tides (e.g., Loria 2018). By NOAA’s definition, Miami experienced nine days of nuisance flooding in 2019. In Southern California, many locations—especially Newport Beach (Orange County) and Imperial Beach (San Diego)—regularly experience nuisance flooding during king tides (Jones-Bateman 2019). Researchers expect the frequency of nuisance flooding to double every five years for locations already vulnerable to nuisance flooding (Taherkhani et al. 2020). NOAA’s Margaret Davidson (1950–2017) put it this way: “Today’s flood will become tomorrow’s high tide” (e.g., Sweet et al. 2018).

Definitions based on fixed tide heights don’t always reflect conditions on the ground. One neighborhood in Key Largo—about an hour’s drive south of Miami—experienced more than 90 days of nuisance flooding in 2019 as a result of king tides (e.g., Mazzei 2019). To protect their cars from saltwater corrosion, residents drive on top of lawn sprinklers to wash away the salts (e.g., The Weather Channel 2019). The challenge of adequately describing hyperlocal impacts of nuisance flooding has led one group of researchers to turn to social media. Using number of tweets and geographic information, the researchers found that users generally did a good job of tracking flooding events (Moore and Obradovich 2020). Some researchers have begun to promote citizen science—reporting and collection of scientific data from the public—to expand flood monitoring and even flood model calibration (e.g., Reineman et al. 2017; Loftis et al. 2019; Golparvar and Wang 2020).

Oceanographers are also concerned about extreme events. When high tides coincide with other phenomena that increase sea level, potentially catastrophic sea level rise may occur. Two of the three strongest El Niños on record—1982–1983 and 1997–1998—resulted in millions of dollars of damage through loss of homes, businesses, and infrastructure, in part, due to increases in sea level (e.g., Cayan et al. 2008; NRC 2012).

The descriptions here only briefly touch on the various causes and consequences of sea level rise globally and locally. While efforts are underway to develop tools, strategies, and solutions for mitigating and adapting to sea level rise, it is unclear whether the public’s sense of urgency has yet been sufficiently awakened. In an October 16, 2020, commentary in the San Diego Tribune, Scripps oceanographer Richard Norris writes:

A recent state report notes that, in 10 years, sea level will be up to a foot higher than it is now. That is not enough to flood much, but add to that the seven additional feet of king tides every spring, and the foot or so of flooding from an El Niño, and even several feet of ocean swell from an ill-timed storm surge, and we step into dangerous territory. In 30 years, the high school fields, the golf course and Campland on the Bay could well be repeatedly underwater along with areas of Pacific Beach, Mission Beach Park, and Marina Village. The time to fix this costly situation is now, so we can make considered plans, instead of being faced with an emergency.

Underscoring these concerns, a recently published paper reported more than half of US coastal communities underestimate the extent of future sea level rise (e.g., Garner et al. 2023). With the ocean already knocking on the door, it’s more important than ever for citizens and policymakers to adopt strategies that ensure the well-being of those who live and work along our coastlines. The coastline is changing, and we’re going to have to change with it.