Photo: Kristin Vogt from Pexels

Sea levels are rising, and will continue to rise, climate models tell us, throughout the century. It is a situation that began in the second half of the nineteenth century, in line with the industrial revolution, and continues at increasingly high rates, putting large segments of the world's population, those living in the most vulnerable coastal areas, in real danger. Risk of exposure to devastating floods.

When thinking about the consequences of sea level rise An additional factor that is often not taken into consideration enough is subsidenceThat is, the “sinking” of the soil (continental or seabed) by natural or human causes.

One StadyIt was conducted by a team of scientists from Virginia Tech together with colleagues from other research institutions and only published In the journal Nature, I provided a comprehensive overview of… Flood risk in 32 US coastal citiesHe concluded that scenarios by 2050 are likely to be worse than previous models indicate. The reason lies precisely in the fact that this is the case Many current forecasts do not accurately assess the contribution of subsidence This exacerbates the vulnerability of areas severely threatened by rising sea levels.

Nature Research Paper: The Disappearance of Cities on the Coasts of the United States https://t.co/8TEkbnQLNl

— Nature (@Nature) March 7, 2024

According to the new study, Rising sea levels could cause flooding in large coastal areas of the United StatesEspecially those located in the eastern part of the country and among the cities at risk of being affected there are also many major cities such as Boston, New Orleans and San Francisco. Researchers expect this to happen in the next three decades Up to 500,000 people could be affected by floods One in 35 private properties is at risk of suffering major damage, especially in areas with a significant lack of coastal defense structures, such as dikes, dikes or dikes (this is especially the case on the Atlantic coast).

Another absolute novelty in the study was the consideration of racial and socioeconomic demographic data related to potentially affected areas, and in this regard the researchers ascertained that in some cities, particularly those along the Gulf Coast, the greatest potential exposure falls disproportionately on people Who find themselves in a state of economic deprivation. “This really doubles the potential impact on those areas and their ability to recover from major flooding.” Comment Leonard Ohnen, first author of the study and a doctoral student at the Earth Observation and Innovation Laboratory at Virginia Tech.

Research team – led by Manouchehr Sherzai, associate professor of geophysics and remote sensing at Virginia Tech, used extremely precise data points measured by space-based radar satellites and constructed some of the first high-resolution representations of land subsidence along the entire coast of the United States. Previous work recently conducted by the same team of scientists and published At the beginning of the year in the magazine BNAS, it was already revealed that some areas of the Atlantic coast are sinking by up to 5 millimeters per year.

The East Coast of the United States has always been a special watch: The region is home to more than a third of the country's total population and climate models already exist to caution Sea levels are likely to rise by 25 to 30 cm above today's levels by 2050. The situation becomes even more alarming in light of data on subsidence, an additional vulnerability factor that also changes significantly over short distances and which is often absent from coastal risk assessments. .

Some of the authors of the paper just published in Nature, including Ohenhen and Shirzaei themselves, have already begun delving into this topic in a study. Stady Which I showed him Cumulative effects Sea level rise and fall. In this previous work, conducted from 2007 to 2020 along 3,500 kilometers of coastline, scientists found that in cities on the Atlantic Ocean, including Boston and New York, the rate of subsidence exceeds 3 millimeters per year. They may seem small, but when combined with an annual rise in water levels of five millimeters, they contribute to increased risk of flooding, destroying infrastructure and buildings, having a negative impact on coastal ecosystems and creating problems for aquifers due to groundwater seepage. salty water.

“In subsidence, even imperceptible millimeter subsidence of land exacerbates existing coastal hazards,” Ohnine noted.

Along with the new flood risk projections, the study also revealed that the 32 cities covered in the research (spread along the Atlantic, Pacific and Gulf coasts) have a total of 131 flood control structures, such as levees, dikes or dikes, but that 50% of them are located on California coast. In fact, the situation along the Pacific coast is generally less alarming, because many areas are at higher elevations, subsidence rates are lower, and conservation interventions are more widespread.

In contrast, the Gulf and Atlantic coasts present greater vulnerability: both have to deal with significant subsidence, but the cities on the Atlantic Ocean are also characterized by inadequate protection structures (levees or dikes are present only in three of the coastal cities on Sunday ten on the Atlantic coast). which the study considers).

“The purpose of this paper is to provide data to support decisions,” Sherzai said in a Virginia Tech press release. In this regard, Al-Muallem added that every city has a plan to mitigate flood risks, but so far there is no complete picture of what could happen in the not-too-distant future.

Coastal subsidence is often underrepresented in inundation models, the authors said. Moreover, this phenomenon changes significantly even over short distances, due to differences in the underlying geology and nearby human activities, such as groundwater extraction or energy sources such as oil and gas.

And in the Mediterranean?

So far we have talked about the situation in the United States however The scenario remains worrying even if we look closer to us, towards the Mediterranean Sea, which is one of the largest exhibition In the face of climate change.

One Stady It was recently created by a team of Italian researchers from the National Institute of Geophysics and Volcanology, in collaboration with Radboud University in the Netherlands. It revised its estimates of sea level rise in the Mediterranean Warning that in some areas The increase is moving at three times the speed of estimates made so farsuch as the forecasts published by the Intergovernmental Panel on Climate Change in 2021 in the AR6 report.

Even in the Mediterranean scenario, subsidence plays “a crucial role in accelerating sea level rise along the coasts, caused by global warming since 1880,” explains Marco Ansidi, a researcher at INGV and co-author of the study.

To conduct the research, scientists used data from several space geodetic stations located 5 kilometers from the sea, which allow calculating the speeds of the Earth's vertical movement with great accuracy. In light of these data, the researchers recalculated the current IPCC projections up to 2150 in 265 regions of the Mediterranean, showing that in the most vulnerable areas there could be significant impacts on the environment, human activities and infrastructure.

As a result of sea level rise, More than 38,500 square kilometers of Mediterranean coast – Only half of it is in the northern sector of the basin – They will soon become more vulnerable to flooding.

Areas most at risk of flooding are in red. Image taken from A Vecchio et al 2024 Environ. Accuracy 19 014050

As can also be seen from the figure created by the study authors, Areas at risk of being particularly affected in the next 100 years One of the consequences of sea level rise I am Egypt (With approximately 13 thousand square kilometers of land potentially at risk) It's Italy, The coastal surface, which is characterized by greater forestry, extends over an area of ​​more than 10,000 square kilometers (including about 4,000 square kilometers in the Po Delta region, where there is constribte What led to the decline was gas extraction, which was widely practiced from the 1930s to the early 1960s, when operations were halted due to the risks involved.)

The study's authors concluded by highlighting the need for concrete action to support residents of the most vulnerable areas, within a framework that also highlights the lack of awareness and knowledge gaps about the causes and expected effects of sea level rise. Owns Important implications for the adaptation policies that will be adopted in the near future to protect the inhabitants of coastal areas of the Mediterranean.