Extreme coastal flooding events will become commonplace at nine-in-10 US coastal sites as sea levels continue to rise around the planet, new research suggests.
Sea level rise is slow but continues to accelerate as climate change increases. Projections under worst-case-scenario estimates suggest that millions of people around the world will be displaced by the end of the century, but even small increments of sea-level rise can disproportionately increase the frequency of coastal flooding, say a cohort of researchers at the US Geological Survey, the University of Illinois at Chicago, and the University of Hawaii.
“Sea-level rise will radically redefine the coastline of the 21st century. For many coastal regions, projections of global sea-level rise by the year 2100 are comparable in magnitude to today’s extreme but short-lived increases in water level due to storms,” write the study authors in Scientific Reports.
Based on historical records, extreme flooding events occur about once every 50 years as their “once-in-a-lifetime” nickname suggests. Coastal flooding is influenced by a number of factors, including tidal fluctuations, storms, and climatic cycles. This data was collected from more than 200 tidal gauges located along the US coastline in order to quantify how frequently flood events are likely to occur based on projected sea-level rise. As sea levels rise, the odds of coastal flooding increases exponentially even under moderate scenarios. By 2050, most coastal cities will see “dramatically higher” flood hazards.
“Combining these growth rates with established sea-level rise projections, we find that the odds of extreme flooding double approximately every 5 years into the future,” write the authors. “This new approach, establishing new flood hazard regimes based on a calendar date, effectively communicates the urgency for sea-level rise planning and adaptation.”
The rate of coastal flooding is expected to double every five years and in the next three decades, 50-year extremes could become annual events at nearly three-quarters of the sites tested. By the end of 2100, once-in-a-lifetime floods are predicted to be exceeded almost every day in 90 percent of cites measured across the US coasts with low-latitude areas being the most susceptible. In susceptible sites in the Caribbean and Hawaii, for example, water level rise is expected to double with every centimeter of sea-level rise.
However, each coast will experience different levels of flooding. In general, the west coast will see smaller levels of sea-level rise whereas the mean increase on the east coast is nearly double, particularly in areas exposed to tropical storms.
“Given established emissions trajectories and sea-level projections, the odds of extreme coastal flooding will double every 5 years into the foreseeable future at most locations in the US. With increased flood frequency, we expect a corresponding acceleration of a number of related coastal hazards, such as beach and cliff erosion,” write the authors.
“Our society has yet to fully comprehend the imminence of the projected regime shifts in coastal hazards and the consequences thereof.”