Land instability Compounds the risk of sea level rise in Alexandria, Egypt

The coastal region of Alexandria Governorate in Egypt holds significant strategic importance for trade while being susceptible to extreme weather events. It confronts a dual challenge of the rising sea levels and, as found in this study, land instability. While much attention has been rightly directed towards sea level rise (SLR), the stability of the land warrants equal consideration. Here, a comprehensive analysis of land stability is conducted in Alexandria by measuring Line of Sight (LOS) displacements and assessing their topographical, hydrological, and coastal impacts. Persistent Scatterer Interferometry technique is used to measure the LOS displacements in association with land cover classification and elevation data. Moreover, in the absence of a recent, openly accessible Digital Elevation Model (DEM) with satisfactory resolution, we developed a novel approach to update DEM using the Small Baseline Subset method. This approach enabled us to generate a projected DEM for the year 2040, facilitating the creation of a stream network based on this “future DEM”. Our observations revealed displacements ranging from −14.0 to 6.7 mm/year, predominantly occurring in low-lying and built-up areas, suggesting anthropogenic activities as a likely cause. The current and future stream networks show stream shifting and widening. Stream shifting indicates dynamic changes in topography and hydrological conditions, while stream widening suggests alterations in the hydrological network due to increased urban runoff or changes in the natural watershed. Furthermore, we found that sea surface temperature and SLR are projected to increase until the end of the century in the Mediterranean Sea near Alexandria. This escalation raises the likelihood of intensified tropical-like hurricane events in the region, commonly referred to as “medicanes”. The importance of this research is in offering a framework for comprehensive land stability assessments, along with demonstrating the scalability of the applied methodologies, including our distinct approach to generating both current and projected DEM.