[CAIRO] Buildings in the ancient Egyptian city of Alexandria have been collapsing at an alarming rate over the last two decades—a fate which could await coastal cities around the world, according to researchers.

Over the past 20 years, the densely populated port city has seen more than 280 buildings collapse—a rate ten times higher than in previous decades—according to the study published in the journal Earth Future.

It says more than 7,000 buildings in the most vulnerable part of the coastline are now at risk of crumbling, making it the most at-risk area of the Mediterranean Basin.

Severe coastal erosion and rising sea levels—a result of climate change—are driving this phenomenon, which is not unique to Alexandria, says the researchers.

Essam Heggy, a researcher at the University of Southern California, USA, who led the team, told SciDev.Net: “Alexandria is a living example of the challenges facing other coastal cities in the region due to climate change and uncontrolled urban expansion.

“The results of the study reflect the potential risks and preventive measures that can be applied globally.”

Coastal erosion and rising sea levels accelerate seawater intrusion into groundwater layers, increasing water and salt levels.

This destabilises the soil and speeds up the corrosion of building foundations, according to the study.

The researchers analysed geographic, geological and engineering data to identify the locations and characteristics of collapsed buildings.

They also used government reports and news archives to monitor damaged or threatened buildings and assessed the development of the coastline using satellite imagery and topographic maps.

“We also conducted a soil settlement analysis in different regions, which revealed a link between poor soil stability and increased building collapses, as well as a statistical analysis of geological change rates to assess the impact of coastal retreat on infrastructure,” said Sara Fouad, a visiting researcher at the Faculty of Engineering and Design at the Technical University of Munich, Germany.

The area hardest hit by extreme erosion is the Gharb district of Alexandria, where the shoreline has retreated by an average of 31 metres a year over the last century, according to the study.

Coastal erosion has led to increased salt infiltration into shallow coastal aquifers a few kilometres inland, negatively affecting soil quality and moisture levels, researchers explain.

The over-extraction of groundwater is exacerbating seawater intrusion, leading to further salt intrusion into coastal aquifers and building foundations, according to the analysis.

Areas that have undergone extensive land reclamation are particularly vulnerable due to damage to the foundations, says Heggy.

He says the problem is made worse by a lack of maintenance of old buildings, poor urban planning, weak sewage infrastructure, and insufficient legislation.

Poor management of the waterfront has also been a factor, believes Fouad. She says a comprehensive approach to risk management and sustainable urban planning is needed.

Other cities at risk

Although the study focused on Alexandria, its results carry warnings for other coastal cities in the southern Mediterranean, such as Tunis and Tripoli.

The study notes that coastal municipalities in Tunisia have reported significant structural damage from beach erosion, particularly in areas experiencing rapid urban expansion.

Building collapse rates along Italy’s southern coast meanwhile have increased by nine per cent over the past two decades, raising concerns about the safety of thousands of buildings.

Amir Gohar, senior lecturer in urban planning and management at the University of the West of England, says widespread urbanisation along Egypt’s North Coast, including the development of coastal tourist villages, is disrupting national sedimentation processes and driving sea levels up.

“Consequently, shoreline erosion, combined with rising sea levels, affects the structural foundations of coastal building strips in major cities,” he said.

He said the impact of sea level rises varies across Mediterranean countries but is “a persistent challenge for the entire region”.

‘Living beaches’

The study proposes environmental and technical solutions based on nature-based “soft defence” techniques, such as green infrastructure and eco-friendly coastal designs, to protect coastal buildings against climate change.

These solutions include so-called “living beaches”, designed to stabilise the shoreline and protect wildlife, as well as breakwaters, rain gardens, and restoration of wetlands, to reduce the risks of flooding, seawater intrusion, and soil erosion.

“We recommend designing a green street network with salt-tolerant plants along the coast, which enhances water absorption and mitigates the impact of high tides,” added Fouad.

Mattheios Santamouris, professor of high-performance architecture at the University of New South Wales, Australia, believes the study provides a strong analysis of the hydro-climatic factors affecting building collapse.

He says better coordination and cooperation with local authorities could help in implementing the preventive measures proposed by the study.

Egypt must adopt strategies for both adaptation and mitigation, adds Gohar.

These could include building sea walls and flood barriers, as well as restoration of mangrove forests and coral reefs, to provide natural defences against storm surges.

Removing buildings and relocating communities away from vulnerable areas should also be considered, says Gohar, as well as implementing regulations to stop the expansion of coastal resorts on the North Coast.

This article was produced by SciDev.Net’s Middle East and North Africa regional office.