A dramatic increase in building collapses in the ancient port city of Alexandria, Egypt, has been directly linked to rising sea levels and the intrusion of saltwater, according to a recent study.
Scientists from the University of Southern California (USC) have found that building collapses in Alexandria, one of the oldest cities on the planet and often referred to as the ‘Jewel of the Mediterranean’ for its beauty, have shifted from being rare events to alarming occurrences.
According to the scientific research, the collapse rate has gone from about one per year to a concerning number of 40 per year in the last decade.
Impact of Climate Change on Alexandria
“The real cost of this loss goes beyond bricks and cement. We are witnessing the gradual disappearance of historic coastal cities, and Alexandria has sounded the alarm. What once seemed like distant climate risks are now an immediate reality,” commented Essam Heggy, a water scientist at USC’s Viterbi School of Engineering and lead author of the study.
For centuries, Alexandria’s structures have stood as wonders of resilient engineering, enduring earthquakes, storm surges, tsunamis, and more. But now, rising sea levels and the intensification of storms, driven by climate change, are eroding in decades what took millennia of human ingenuity to build.
Even minimal increases in sea level, just a few centimeters, can have devastating effects, Heggy stated, threatening even ancient and resilient cities like Alexandria, which has withstood centuries of earthquakes, invasions, and fires, as well as modern metropolises like Los Angeles, where flash floods and landslides now complicate the recovery from recent wildfires.
Triple Analysis Approach
Published in Earth’s Future, the study used a triple analysis approach to assess the impact of changes in the coastline on Alexandria’s buildings.
First, a detailed digital map was created using geographic information system technology to identify the locations of collapsed buildings in six districts of the historic urban area of the city, one of its most densely populated regions.
The map catalogs key details about each structure, including its location, size, construction materials, age, foundation depth, and number of floors.
The data, collected from site visits, government reports, news archives, and statements from private construction companies, span from 2001 to 2021 and include both fully and partially collapsed buildings.
Next, satellite images were combined with historical maps from 1887, 1959, and 2001 to track the coastal movement and gain a deeper understanding of how parts of Alexandria’s 80-kilometer coastline have shifted tens of meters inland over the past two decades.
Combating Coastal Erosion
By calculating the rate of coastal retreat over the last century, researchers examined how coastal reduction is raising groundwater levels, bringing them into contact with the foundations of coastal buildings.
Finally, the team analyzed chemical fingerprints known as isotopes in soil samples to examine the effects of saltwater intrusion. They measured specific isotopes, such as B7, in each sample to evaluate the mechanical properties of the soil. Higher levels of B7 indicate stronger and more stable soil, while lower levels suggest erosion.
“Our isotope analysis revealed that buildings are collapsing from the bottom up, as saltwater intrusion erodes foundations and weakens the soil. It’s not the buildings themselves, but the soil beneath them that’s affected,” detailed Ibrahim H. Saleh, a soil scientist at the University of Alexandria and co-author of the study.
“Our study demonstrates that coastal buildings are at risk of collapsing even without direct saltwater intrusion as commonly believed,” Heggy added.
To combat coastal erosion and saltwater intrusion, researchers propose a nature-based solution: creating sand dunes and vegetation barriers along the coast to block saltwater invasion and prevent saltwater intrusion from raising groundwater levels to building foundations.
This sustainable and cost-effective approach can be applied in many densely urbanized coastal regions globally, highlighted Steffen Nijhuis, a landscape urbanist at the University of Alexandria.
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