KEY TAKEAWAYS: Tulane-led study finds 100-year coastal floods now occur about 12 times more often worldwide. Researchers say climate change has made extreme coastal flooding roughly four times more likely since 1900. Study highlights growing need for updated flood planning and resilient coasta l infrastructure. Findings reinforce the importance of maintaining New Orleans‘ post-Katrina flood protection system.   A new study led by a Tulane University researcher has found that human-caused sea-level rise has significantly increased the frequency of extreme coastal flooding around the world, with floods once expected only every 100 years now occurring about 12 times more often on average. The research, published in the journal Nature Climate Change, concludes that climate change has made these rare flooding events roughly four times more likely since 1900. Researchers said the findings underscore the growing challenges facing coastal communities and the need for continued investment in flood protection and long-term resilience. The study was led by Sönke Dangendorf, the David and Jane Flowerree Associate Professor in River-Coastal Science and Engineering at Tulane University’s School of Science and Engineering, in collaboration with an international team of researchers. The team analyzed long-term tide gauge records and climate model simulations to distinguish the effects of human activity, natural climate variability and local land movement on rising sea levels and flood frequency. “Extreme sea levels occur when high tides, storm surge and rising baseline sea levels combine. As sea levels rise, smaller storms can produce flooding that previously required more severe conditions,” Dangendorf said. “At nearly half of the 130 sites analyzed in the study, a flood expected once every 100 years in 1900 now occurs at least once per decade.” Researchers found the increase in flood frequency varies by location. At Sandy Hook, New Jersey, what was once considered a 100-year flood event had become roughly a 16-year event by 2005. In Wellington, New Zealand, a similar event now occurs about twice each year. The study also identified local factors that can worsen flood risks. In Manila, land subsidence associated with groundwater extraction has increased the frequency of extreme flooding by more than 300 times. However, researchers said human-caused climate change remains the primary driver behind rising flood risk at most of the 130 locations studied. The findings have implications for coastal infrastructure planning, insurance and flood risk management, as historical estimates of flood frequency may no longer accurately reflect current conditions. The research also highlights the importance of maintaining flood protection systems in cities such as New Orleans, which has invested heavily in hurricane and flood defenses since Hurricane Katrina. “New Orleans has made enormous progress in reducing flood risk after Katrina,” Dangendorf said. “Our results show that as environmental conditions continue to evolve, sustained maintenance and forward-looking planning are key to preserving that level of protection.” According to the study, natural climate variability played a larger role in sea-level changes during the early 20th century, but the influence of human-caused warming has steadily increased since the 1960s and now represents the largest contributor to rising sea levels and associated coastal flood risk. Dangendorf said the findings demonstrate that continued adaptation and infrastructure investment will be essential for coastal communities seeking to manage growing flood threats. “New Orleans is a global example of how to manage coastal risk,” Dangendorf said. “Our work highlights that with continued attention and adaptation, that leadership can be maintained even as conditions change.” ...read more read less