(C) Verite News New Orleans This story was originally published by Verite News New Orleans and is unaltered. . . . . . . . . . . Local experts question major study on sinking land and flood risk [1] ['Drew Costley', 'More Drew Costley', 'Verite News'] Date: 2024-03-08 A national study published in the prominent science journal Nature this week found that well over 100,000 more people in greater New Orleans could be exposed to high-tide flooding by 2050, but local experts are questioning the validity of the study’s findings. Scientists from Virginia Tech and their colleagues examined how land subsidence — the sinking of land — can affect exposure to sea-level rise for 32 coastal cities in the United States. They found that in the New Orleans area, between 97,000 and 170,000 more people, hundreds of more square miles and tens of thousands more properties could be exposed to high-tide flooding because sinking land is exacerbating the effects of sea-level rise. The study’s lead author, Leonard Ohenhen, a PhD candidate studying geoscience at Virginia Tech, said cities in the Gulf Coast are sinking the fastest and that Biloxi, Mississippi and Corpus Christi, Texas have the largest median rates of sinking. But, he said, New Orleans will have the largest amount of people, property and land exposed to high-tide flooding by 2050 because the city is already below sea level. The authors also found that people of color who live in areas with low property values in New Orleans, along with the rest of the Gulf Coast, will take on a disproportionate share of the risk. Local experts on subsidence and coastal flooding who spoke to Verite News about the study agree with many of its conclusions and applauded its focus on the intersections between subsidence, race and socioeconomic status. But several took issue with how the study calculated projections of how many people who could be exposed to flooding, saying the study applied broad assumptions across all 32 cities, failing to fully account for local factors. The experts said the study could’ve taken a closer look at its local-level findings and consulted local experts. “There is really a lack of ground truthing,” said Torbjörn E. Törnqvist, a geology professor at Tulane University. “There is a lot going on at the local level and in some places you have very unique conditions. And of course, New Orleans is a really good example of that.” For one, experts said that the study did not fully account for coastal protections in the greater New Orleans area. The study itself says it projected future flood risk in cities assuming a lack of coastal defense. But that doesn’t work for greater New Orleans because the region has its own unique combination of coastal flooding protections, such as barrier islands in the Gulf of Mexico, marshland and the city’s $14.6 billion levee system constructed by the U.S. Army Corps of Engineers in the years after Hurricane Katrina. These can mitigate many of the risks that the study authors were looking at. New Orleans is most often flooded from strong stormfronts, not from high tides exacerbated by sea-level rise. “I think that they’re making a set of assumptions and applying those assumptions to every city. And I don’t think that those necessarily apply to New Orleans,” said Alex Kolker, an associate professor at the Louisiana University Marine Consortium who studies the way coastal systems function. Another persistent critique of the study was that it hedges on the question of whether the levee system in New Orleans would provide adequate protection from floods. In the study, the authors acknowledge the city’s flood protection system and the failure of the federal levees after Katrina. But it does not appear to take into account that the system was recently rebuilt or say exactly how the existing protections would impact the level of exposure. And on the question of how much the land is subsiding in coastal Louisiana, the authors found that much of the coast is subsiding at a significantly lower rate than what was found in previous studies, like one by Törnqvist and colleagues from 2017 and another by the state’s Coastal Protection and Restoration Authority from 2021. Experts who read the paper said they are inclined to trust previous findings. Finally, experts pointed out that much of the additional area exposed to high-tide flooding by 2050 is outside of the city limits, some of which has much lower population density than the city. “For New Orleans, for the kind of flooding that they’re looking at, I think they’re probably overestimating exposure,” said Denise Reed, a professor at the University of New Orleans who studies coastal wetlands. Those factors shaped the study authors’ findings regarding how many more people and how much land and property will be exposed to high-tide flooding by 2050. And that makes it hard for local scientists to gauge how much they can trust the findings on exposure. Törnqvist said he couldn’t tell whether the study authors were under- or overestimating future flood exposure. “There may be places where it’s overestimated, and it may be out of places where it’s underestimated,” he said. “I’m concerned about the the actual results.” When asked about his level of confidence in the study’s findings, Ohenhen said the research was peer-reviewed and went through several edits and corrections before it was published by Nature. The study authors did not respond to requests for additional follow-up questions based on the critiques of local experts by publication time. ‘I hope they do everything they can’ Despite their critiques, the local scientists who spoke with Verite News said it’s vital to think about land subsidence when considering future flood risk and highlighting the disproportionate effect of climate change on poor communities and communities of color. Reed said the study authors used a new approach to gauging subsidence that local experts should investigate further. The approach involves bouncing signals off of surfaces from satellites and aircraft and gauging the height of the surface from how long it takes the signal to get back to the satellite or aircraft. “It’s always good to… have new sources of data for us to look at,” she said. “We don’t have to trust them right off the bat, right? We [should] get to them and see what they mean and check the methods.” This study comes out at what may be a particularly critical time for Louisiana — two months after the inauguration of Gov. Jeff Landry. Landry, who once infamously said climate change is a hoax, took office in January and began making moves to benefit industries that could worsen climate change by continuing to emit carbon into the atmosphere. That includes appointing a number of former oil, gas and coal executives to environmental posts, committing to having the most robust oil and gas refining operations in the country and opposing President Joe Biden’s push to expand the manufacture of electric vehicles. Most local scientists who read the study and spoke with Verite said they’re unsure how its findings could be used to inform state and local environmental, climate and coastal policy. But they did say that it does a good job of underscoring the fact that coastal Louisiana is at risk, even if they question its conclusions about the scope of that risk. Barry Keim, a climatologist at Louisiana State University who recently was removed from his post as the state climatologist, said more needs to be done to protect the state’s coasts to buttress the defenses that are already in place. “I just hope the current administration takes Louisiana’s coasts very seriously,” he said, “because it’s in the best interest of the constituents of Louisiana to have a healthy, vibrant coastal ecology that takes us into the future. So I hope they do everything they can.” Related Stories Republish This Story Republish our articles for free, online or in print, under a Creative Commons license. [END] --- [1] Url: https://veritenews.org/2024/03/08/local-experts-question-major-study-on-sinking-land-and-flood-risk/ Published and (C) by Verite News New Orleans Content appears here under this condition or license: Creative Commons BY-NC-ND 3.0 US. via Magical.Fish Gopher News Feeds: gopher://magical.fish/1/feeds/news/veritenews/