Adaptive Coastal Transformation to Mitigate the Increasing Risks of Building Collapses in Low-Lying Littoral Cities in North Africa

Several North African coasts, including low-lying sandy and deltaic areas, are at high risk of coastal hazards due to increased climatic fluctuations. Alexandria, a historic and densely populated Mediterranean port city that is representative of several coastal cities in North Africa, has experienced over 280 building collapses near its shorelines over the past two decades, with the root causes still being investigated. To address the potential causes, we explore several anthropogenic and hydroclimatic drivers along the coastline of Alexandria using a GIS-based multi-criteria analysis in the areas where buildings collapsed from 1974 to 2021. We considered both the coastal physical properties and the buildings’ structural elements. Our results suggest that collapses are correlated to severe coastal erosion due to sediment imbalance caused by the decades-long inefficient landscape and urban expansion along the historic city’s waterfront. This severe erosion increases seawater intrusion, which in turn raises the groundwater levels in coastal aquifers, disrupting soil stability and accelerating corrosion in building foundations until they collapse. We identified a littoral area of high vulnerability with over 7,000 buildings at risk, surpassing to an extent any other vulnerable zone in the eastern Mediterranean Basin. We conclude that coastal and densely urbanized areas in North Africa are at greater risk of being affected by hydroclimatic extremes, which can lead to higher risks of building collapses. Therefore, we propose a landscape-based coastal mitigation approach to perform adaptive transformation to curb these risks.