Abstract

The low-lying, arid coastal regions of the Southern Mediterranean basin, extending over 4600 km, face daunting sea level rise and hydroclimatic changes due to shifting weather patterns. The impacts of the above on coastal urban buildings and infrastructure still need to be more qualified and understood. Alexandria, a historic and densely populated port city representative of several coastal cities in the Southern Mediterranean, has experienced over 280 building collapses near its shorelines over the past two decades, with the root causes still being investigated. We explore the decadal changes in coastal and hydroclimatic drivers along the city's coastline using a GIS-based multi-criteria analysis in the areas where buildings collapsed from 1974 to 2021. 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, combined with sea level rise, upsurges seawater intrusion, which raises the groundwater levels in coastal aquifers, disrupting soil stability and accelerating corrosion in building foundations until they collapse. We identified a coastal area of high vulnerability with over 7,000 buildings at risk, surpassing any other vulnerable zone in the Mediterranean Basin. We conclude that several coastal and densely urbanized areas in the Southern Mediterranean are at greater risk of building collapses due to similar hydroclimatic changes. Therefore, we propose a landscape-based coastal mitigation approach to implement adaptive transformations to curb these risks that apply to Alexandria and other southern Mediterranean cities facing the same challenges.