In Alexandria, Egypt, building collapse rates have increased, according to a published study from the Keck School of Medicine. ​​The study, published in the scientific journal Earth’s Future on Feb. 12, found that over the past two decades, collapse rates in Alexandria have surged by 40%, and warned that similar effects could hit Los Angeles.

“California [has] the same characteristics,” said Oula Amrouni, a contributor to the study and associate professor at the University of Carthage. “We have the temperate climate … We have the same sandy beach and the same risk.”

The study was a collaboration between USC, the Technical University of Munich and the University of Carthage, which initially aimed to investigate the physical connections between rising seas, groundwater changes and structural instability.

Essam Heggy, a USC scientist who co-authored the study, said disbelief in climate change has made preparing for these risks harder.

“People who don’t believe in climate change think that we have it all,” Heggy said. “When we talk about sea level rise in 50 years, people think it’s a joke.”

The researchers tracked Alexandria’s shoreline retreat using satellite imagery, Geographic Information System mapping and field surveys. They documented both visible damage and hidden risks underground.

As seawater intrudes into freshwater aquifers beneath coastal cities, it pushes up groundwater, Heggy said. Rising saltwater infiltrates building foundations from below, corroding them slowly over time.

“Salt water that is intrusive in this aquifer, and this aquifer when it has salt water, will penetrate in your house,” Amrouni said. “My office is in front of the sea, every year we need to mix some paint because we have salt coming from the [floor].”

Co-author Sara Fouad, a landscape architect at the Technical University of Munich, spent months documenting collapsed structures in Alexandria by comparing historical maps to satellite images dating back decades to measure how much the coastline has retreated, Fouad said. In some areas, Alexandria’s beaches had shrunk by more than five meters per year — far faster than expected.

Although Alexandria and Los Angeles differ in some geography — Alexandria is low-lying, while parts of Southern California are bordered by cliffs — Heggy said the parallels are troubling.

“All these beautiful houses we build on the coastline of California do damage,” Heggy said. “They act as a barrier to transport these sediments to the coastline.”

Traditional methods, such as seawalls and beach nourishment, may no longer be sufficient to protect cities like Alexandria or LA, the study states. Instead, researchers proposed taking approaches based on restoring natural defenses.

“The solution now is based on the ecosystem,” Amrouni said. “Nature doesn’t like artificial barriers. Nature wants a natural barrier.”

These nature-based solutions not only slow erosion but also provide habitats for wildlife and improve overall coastal resilience, Amrouni said.

Beyond infrastructure, Heggy said changing public perception is crucial as “people don’t believe” coastal erosion is a problem. Without public support for adaptation measures, he warned, many coastal communities may be caught unprepared.

The researchers plan to apply their methods to study the changing coastlines of other vulnerable cities, including potential future studies of Los Angeles’ coastline, Fouad and Heggy said.

For Amrouni, the loss is not just scientific or economic — it’s personal. She pointed out that natural beaches can take thousands of years to form, time that future generations may not have if today’s coastlines are allowed to vanish.