The study was just published in the journal Environmental Research Letters.
"Most studies focus on the direct effects of inundation," said lead author Nadia Seeteram, a postdoctoral researcher at Columbia University's Lamont-Doherty Earth Observatory. "Here, we were able to look at flooding on a very granular level, and add in other vulnerabilities."
The study combines building-by-building projections of flooding caused by direct sea-level rise, rainfall or storm surge with fine-grained demographic data to determine how residents will be affected. Along with flood maps, the researchers used U.S. Census Bureau data to chart economic and social factors that would make people more or less vulnerable, including age, race, level of education, income and status of employment, and whether they owned or rented their homes, among other measures. They then divided the population into four categories.
With a one-meter sea-level increase-a middle-of-the-road scenario for the end of this century-56 percent of the population, primarily on higher ground, could face pressures to relocate, they say. The researchers call these people "displaced."
The next largest group they labeled the "trapped"-some 19 percent of the population, living in chronically flooded territory, but without the means to flee to safer nearby ground. About another 19 percent would be "stable," according to the researchers-living in areas not prone to flooding and able to remain there. Just 7 percent-basically the wealthiest, which the researchers labeled as "migrating"-would be directly exposed to flooding in waterfront or low-lying areas, but able to move to safer spots within the metro area.
Not surprisingly, the study says that if sea levels rise even more than a meter, direct flooding, not economic pressures, will become the dominant force affecting residents. At two meters-fairly high amid the current range of estimates, but not out of the question-about 55 percent of the population will be directly inundated through a combination of high sea level and, to an increasing extent, rainfall. Under this scenario, 49 percent of the population would become trapped, and 25 percent displaced. Only 8 percent would be classified as stable.
"This is where it gets to be more drastic, more existential," said Seeteram, who did much of the research during her Ph.D. studies at Florida International University. In either scenario, she said, the results would include potential depopulation of the area and devaluation of flooded properties, as people flee to safer inland regions. This could make it increasingly difficult for authorities to collect taxes to fund adaptations of infrastructure to keep the ocean at bay-a circular process that could send Miami-Dade into an increasingly dire downward spiral, both physical and fiscal.
The study does not look at how many people are currently being affected by flooding, either directly or indirectly. But floods have already become a routine part of life, as monthly peaks in tides percolate up through the sewers during so-called sunny day flooding, and rain with nowhere to drain pools in streets. The kind of flash flooding in New York City that made big news after a big storm at the end of September would be viewed as just another day in parts of Miami during the May-October wet season, said Seeteram. A still unpublished survey by Seeteram and colleagues indicates that nearly three quarters of Miamians say they have been personally affected by flooding from rainfall in one way or another.
There are also some indications that so-called climate gentrification-the displacement of lower-income people from higher-elevation areas predicted by the study-is already taking place. For instance, in the last few years, the Little Haiti neighborhood, a relatively lofty 10 feet above sea level, has seen a sudden surge in development and property values, worrying the largely Black residents that they may not be able to remain.
Study coauthor Katharine Mach of the University of Miami said there is a great, raging debate" about whether climate gentrification is underway. "I suspect it is already happening," she said. However, she said, at least for now, other factors may be playing larger roles in rapidly shifting real-estate values, including longtime pro-development policies and what she calls "real-estate tourism," with speculators snapping up relatively inexpensive properties in a still booming region. "The question is, what fraction [of rising prices] can you put on climate?" she said. She pointed out that real-estate prices are also going up in low-lying and waterfront areas, but not as fast as in less flood-prone areas-one possible indicator that predicted sea-level rise is playing a role in buyers' decisions.
Seteeram said the projections in the new study may not necessarily come to pass, at least with lower estimates of sea-level rise; it depends on how the metro area confronts the problems in coming years. If it revamps infrastructure to lessen flooding and takes other measures, that could blunt the effects, she said. "We could see different kinds of housing development, to make the population denser in some areas, or more climate resilient. But then you would have to see what the intersection would be with affordability for a lot of people."
The other authors of the study are Kevin Ash of the University of Florida, Gainesville, and Brett Sanders and Jochen Schubert of the University of California, Irvine.
Research Report:Modes of climate mobility under sea-level rise
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