Extreme Coastal Flooding Could Be Daily Event by 2100

Once-in-a-lifetime flooding events could be a daily occurrence in coastal cities, thanks to rising sea levels due to climate change.

People make their way in a flooded St. Mark’s Square in Venice, Italy, in November 2019. The city experienced tides of exceptional levels and its worst flooding in more than 50 years. (AP Photo/Luca Bruno)

(CN) — A study revealed Thursday that if sea levels continue to rise at their current rate, the extreme flooding events seen in select U.S. coastal areas could potentially double in frequency every five years.

In the study, published Thursday in the journal Scientific Reports, researchers discuss how today’s once-in-a-lifetime extreme water levels — 50-year events — may be exceeded daily along most of the U.S. coastline before the end of the 21st century.

Global sea levels have been rising at an alarming rate over the past century and more so over the past few decades, totaling at about an eighth of an inch per year according to the National Oceanic and Atmospheric Administration.

In the United States, about 40% of the nation’s population lives in coastal areas at risk of hazards such as flooding, shoreline erosion and storm hazards. On a global scale, eight of the world’s largest cities are located on coasts.

This phenomenon of increasing sea levels is caused by two major factors: thermal expansion from warmer waters and melting from land-based ice. With the former, the oceans act as a sort of sponge for the atmosphere, absorbing more than 90% of atmospheric emissions caused by human activity, including heat that causes the waters to expand.

Authors Mohsen Taherkhani, Sean Vitousek and colleagues at the U.S. Geological Survey, the University of Illinois at Chicago, and the University of Hawaii, investigated these extreme water levels with the help of 202 tide gauges along the U.S. coastline and combined the data with sea-level rise scenarios to model the rate at which flooding events may increase in the future.

They found that 73% of the tide gauges they used had a difference in water level between the 50-year extreme water level and the daily average highest tide of about less than one meter, in contrast to most sea-level rise projections that exceed one meter by 2100.

These sea level increases bring a plethora of environmental consequences, but some of the most concerning are the damages that could be done to coastal populations. Human infrastructure and wildlife habitats will be massively at risk due to destructive erosion and increased storm surges.

Ocean water reaching closer inland will result in those deadly storm surges to push farther inland than they presently do, causing much more frequent flood damage. In fact, some scientists say that some small island nations are at risk of disappearing entirely.

Additionally, when glaciers and ice sheets melt or break off into the ocean, particularly from Antarctica and Greenland, the results can be a drastic increase in sea levels. To put it in perspective, if the whole mass of the ice sheets in Greenland melted into the sea today, it would result in a staggering 23 feet increase in worldwide sea levels.

The authors’ model predicted that before 2050, current extreme water levels transitioned from 50-year, once-in-a-lifetime flooding events to annual events in 70% of US coastal regions. Before the end of 2100, once-in-a-lifetime extremes were predicted to be exceeded almost daily for 93% of the sites measured.

The resulting data suggests that the extreme water levels experienced today pose a threat to become commonplace within the next few decades. The authors predict that low-latitude areas will be the most susceptible under these new conditions, with their rate of coastal flooding predicted to double every five years.

The most susceptible sites will likely be along the Hawaiian and Caribbean coasts, where the rate at which extreme water levels occur may double with every centimeter of sea-level rise.

It is expected that these weather events will increase the number of subsequent coastal hazards. The authors suggest that hazards such as beach and cliff erosion, will likely accelerate in concert with the increased risk of flooding.

Overall, the scientists say it is becoming increasingly important to recognize the causes and effects of what global sea level increases in order to put in place effective solutions and precautions.

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