CNN
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The historic Egyptian city of Alexandria — the birthplace of Cleopatra — is experiencing a “dramatic surge” in building collapses linked to coastal erosion and rising levels of the Mediterranean Sea, new research has found.
Building collapses were once rare in this port city, but have accelerated from approximately one a year to a staggering 40 a year over the past decade, as sea levels rise and seawater seeps beneath city foundations, according to the study published this month by the University of Southern California.
Founded by Macedonian ruler Alexander the Great more than 2,000 years ago, Alexandria is one of the oldest cities in the world and is currently among the most populated in Africa, home to 6 million people. It’s also one of the most vulnerable to sea level rise, which threatens its historical heritage.
Nestled between the thousands of modern, mid-rise buildings are ancient structures designed and erected over centuries by Alexandria’s diverse ruling dynasties.
They have endured natural disasters, including earthquakes and tsunamis, but now rising seas and intensifying storms, both driven by human-caused climate change, are “undoing in decades what took millennia of human ingenuity to create,” said Sara Fouad, lead author on the study and a landscape architect at the Technical University of Munich.
The researchers analyzed the impact of shoreline changes in Alexandria using a variety of methods.
They created a digital map to identify locations of collapsed buildings and cataloged details about each one using data collected from site visits, government reports, news archives and statements from private construction companies, spanning twenty years from 2001 to 2021.
They combined satellite imagery and historical maps from three different years — 1887, 1959 and 2001 — to better understand how Alexandria’s 50-mile coastline has moved dozens of feet inland over the past 20 years, raising groundwater levels and bringing them into contact with the foundations of coastal buildings.
The scientists also analyzed isotopes in the soil to understand the impacts of seawater intrusion. This “revealed that buildings are collapsing from the bottom up, as seawater intrusion erodes foundations and weakens the soil,” said Ibrahim H. Saleh, a soil radiation scientist at Alexandria University in Egypt and one of the study’s co-authors.
Even a small increase in sea levels — “just a few centimeters” — can have devastating effects, said Essam Heggy, a water scientist at USC and a study author.
About 7,000 old buildings in Alexandria are at risk of collapse, the study found.
Last year a building fell in the Wardiyan neighborhood of the city, killing four people, and two years ago a 14-story building popular with domestic tourists collapsed. Although initially unclear how the building collapsed, researchers are pointing to encroaching groundwater damage as a possible reason, the Technical University of Munich’s Fouad said.
The researchers have proposed creating sand dunes and vegetation barriers along Alexandria’s coastline to block the encroaching seawater and prevent it from seeping under buildings.
“This sustainable, cost-effective approach can be applied in many coastal densely urbanized regions globally,” said Steffen Nijhuis, a landscape-based urbanist from Delft University of Technology in the Netherlands and study co-author.
Alexandria is not alone in facing threats from sea-level rise and coastal erosion as the world warms. Many Mediterranean coastal cities face similar risks, as do parts of California’s coastline.
“Our study challenges the common misconception that we’ll only need to worry when sea levels rise by a meter,” Heggy said. “However, what we’re showing here is that coastlines globally, especially Mediterranean coastlines similar to California’s, are already changing and causing building collapses at an unprecedented rate.”