Development of a coastal vulnerability index using analytical hierarchy process and application to Ravenna province (Italy)

The assessment of coastal vulnerability to natural hazards is a major concern in coastal areas worldwide, particularly in the context of climate change and increased coastal development. In this work an index of physical vulnerability to sea level rise and marine floods was designed and applied over the coast of the Ravenna Province (Italy), a low-lying coastal area historically known as being susceptible to coastal flooding and erosion. The index is intended to be at the same time scientifically sound and easy to apply, so it is composed of five relevant variables (elevation, dunes, artificial protection structures, shoreline change rates, and land cover) that were weighted by using a multi-criteria decision making approach, namely the analytical hierarchy process. The weightings were assigned by experts familiar with coastal processes in the area, and all with background in environmental science. This enabled a transparent approach on integrating established expert knowledge to assign the relative importance of the variables in defining vulnerability scores. The final vulnerability score for each segment along the investigated coast was calculated by applying the weighted sum of all variables. For verification purposes, the obtained vulnerability ranking was compared to existing coastal flood hazard maps developed by regional authorities in the framework of the EU Floods Directive (2007/60/EC), and to real inundation events generated by historical storms. The integration of this framework into geographical information systems resulted in informative maps, useful to a variety of end-users such as coastal managers and decision makers.