The study focusing on flood levels along the U.S. East and Gulf Coasts found that 22 counties experience nuisance flooding at water levels much lower than what an official gauge would register as a flood. Cities in the counties include New York, Miami and Boston, which have a combined population of over 13 million people.
"Our analysis implies that large populations might currently be exposed to nuisance flooding not identified via standard measures," said the report by Frances C. Moore of the University of California, Davis' Department of Environmental Science and Policy and Nick Obradovich of the Max Plank Institute for Human Development in Berlin.
To conduct their analysis, the scientists turned to Twitter.
As the climate crisis intensifies and natural disasters become more frequent and powerful, scientists are increasingly turning to social media as a way to assess the damage and impact on a more localized scale.
In this case, Twitter was useful because the 3,700 miles of the East and Gulf Coasts have only about 132 tidal gauge stations. This means it's difficult to measure the impact of changing water levels on specific areas.
"The extent of flooding may be highly variable within a small geographic area, depending on local topography," the scientists said. Additionally, the consequences of higher water levels vary across regions. For instance, two areas could experience the same amount of flooding, but one could include a frequently trafficked road, while the other could be on farmland.
Given the geographic reach of Twitter, as well as the volume and location-specific nature of tweets, the platform can be used to track "nuisance coastal flooding that is both more regular and less consequential," the researchers said. Because the consequences of this type of flood are annoying rather than deadly, they're not always measured or recorded.
The scientists analyzed 5 million tweets between March 2014 and November 2016 that mentioned flood-related terms and were located in a county along the shoreline.
To monitor changes in Twitter activity, they defined a "remarkable threshold" for coastal flooding as when county-specific Twitter posts increased by 25%. They then compared this data with official flood records. "Minor tidal flooding that is remarkable to residents happens at a tide height different from that defining minor coastal flooding," the scientists concluded.
The researchers noted that while flooding caused by high tides and storm surges is already increasing, it's set to become "more frequent and severe as sea-levels rise globally."
This is not the first academic paper to harness the power of social media. The authors pointed to several previous studies that relied on social media, including a 2016 report that focused on using social media to access disaster damage and a 2019 paper that used Twitter to measure damages from earthquakes.
Several drawbacks and inconsistencies come with using social media, the researchers noted.
For one, Twitter is a self-selecting crowd and subset of the population. Prior research has also shown that the more people experience things, the less remarkable they become. In other words, while someone may have tweeted about the first few floods they experienced, after a while it becomes commonplace rather than notable. Additionally, places that experience frequent flooding could bolster their infrastructure, meaning still-recurring higher water levels would be less noticeable.
However, several studies have warned about the danger to coastal communities as sea levels rise.
"Coastal floods and inundation are projected to produce some of the primary social impacts of climate change, imposing significant costs on communities around the world," the report concluded.