Potential tsunami risk assessment to the city of Alexandria, Egypt

Tsunami extreme events present a highly significant hazard and considerable risk to the coastal communities. The continued occurrence of tsunami incidents, together with population growth, increases the risk in coastal communities. Two known catastrophic historic tsunamis in Alexandria occurred in the years 365 and 1303 AD, with reported wave heights of 1 m and 2.9 m, respectively. Approximately 5000 people lost their lives and 50,000 homes were destroyed in the city after the earthquake in 365. The 1303 tsunami destroyed the great lighthouse of Alexandria, one of the seven wonders of the ancient world. In order to avoid such events in the future, a detailed knowledge about the tsunami phenomenon and its potential risk is needed. In this paper, the vulnerability and risk to the city of Alexandria will be examined by remote sensing and GIS techniques considering three scenarios. Methodology used depends on building a comprehensive GIS in addition to recent satellite images. After digitizing raster data, it was then stored into a vector format. A digital parcel map was created; attributes (like distance to shore line, elevation, land use/cover, and population) for each polygon were added. Using the Shuttle Radar Topography Mission images, a digital elevation model was created, to test all the tsunami scenarios (based on 5 m, 9 m, and 20 m wave's height). Finally, vulnerability analysis including physical as well as social and economic constraints was executed for the determination of the vulnerability level of elements. Results indicated that Alexandria city is highly vulnerable to tsunami hazard. Very high risk covers the biggest portion of the area in Alexandria (49.16% and 58.71%), followed by high risk (30% and 28.41%), medium risk (13.61% and 7.76%), and low and very low risk (20.82% and 12.88%).