Remote sensing-based assessment of tsunami vulnerability and risk in Alexandria, Egypt

Tsunamis can cause catastrophic loss of life, destruction of property, engineered structures and coastal infrastructure, and they can lead to major economic losses. Even though tsunamis are relatively rare in the Mediterranean Sea, their potential danger to cities along the Mediterranean coast cannot be neglected. In order to create awareness among the potentially affected people it is important to know the risk and vulnerability of the population and infrastructure related to a possible tsunami impact. In this work a hazard, vulnerability and risk analysis for buildings in two districts of Alexandria was carried out. Relevant input parameters were derived mainly from remote sensing and field data and were analyzed with a geographical information system (GIS). Based on historical records of past tsunamis, two inundation scenarios of 5 m and 9 m were defined and modeled applying a bath-type model. The resulting tsunami building risk zone maps showed that 12% of the buildings in El Gomrok district are at high or very high risk for the 5 m scenario, while the risk for El Montazah area is low. For the 9 m scenario, on the other hand, the majority of the buildings in both districts, 56% of El Gomrok, and 60% of El Montazah, are in the high or very high risk zone. An analysis of the building use indicated that the majority of these buildings are residential and commercial types, highlighting that the potential consequences of a tsunami could be severe. Due to the scarcity of historical data no frequency could be associated with the two selected scenarios. While both are credible we consider the 5 m scenario as possible but unlikely and the 9 m scenario as unlikely.

► Digital surface and elevation model were generated from VHR stereo satellite data.
► Physical vulnerability of buildings was calculated deriving relevant parameters from VHR stereo satellite data.
► Tsunami risk was assessed relating the modeled hazard to the calculated physical vulnerability.
► In a 9 m flood scenario >50% of the buildings are located in the very high risk zone.