An integrated indicator-based approach for constructing an urban flood vulnerability index as an urban decision-making tool using the PCA and AHP techniques: A case study of Alexandria, Egypt

Several cities are exceptionally vulnerable to flood impacts due to increasing urbanization, population growth, and climate change. Quantifying flood vulnerability is useful for identifying the system's weakness, monitoring its evolution, and supporting targeted flood risk adaptation policies. One of the vital aims of assessing urban flood vulnerability is to create an understandable link between flood vulnerability conceptual theories and the daily decision-making process through an easily accessible tool. Although several studies have described the development of an integrated flood vulnerability index (FVI) combining physical, social, and economic dimensions in urban areas, this index has not been assessed in developing countries. Therefore, this study focuses on an integrated indicator-based approach to develop an urban FVI based on exposure, susceptibility, and resilience to urban flooding at the neighbourhood scale. To evaluate the flood vulnerability of the population, we used the Improvement of Vulnerability Assessment in Europe (MOVE) framework. Accordingly, the vulnerability indices cover exposure, susceptibility and resilience aspects. The index is applied to Alexandria, one of the most important coastal cities of Egypt, which is highly vulnerable due to its dense population, low adaptive capacity, flat topography, and exposure to various water-related disasters, such as cyclones, storm surges, bank erosion, sea-level rise, tidal floods, and frequent urban floods. In this study, we use inductive principal component analysis (PCA) to develop a composite indicator for the FVI and to evaluate the vulnerability of 101 census administrative units (sheyakhahs) in Alexandria. We apply the Kaiser-Meyer-Olkin (KMO) test and Bartlett's test of sphericity to assess sample adequacy and perform data standardization for all indicators. Furthermore, the analytic hierarchy process (AHP) is adopted for simplicity and comparison with the PCA results to assess their robustness. We clustered 58 and 13 flood vulnerability-related indicators into three major dimensions, i.e., physical, social, and economic, through PCA and the AHP, respectively. Official collected data are analysed using combined methods using advanced statistical analysis (SPSS) software and a geographic information system (GIS). The findings highlight the variability in flood vulnerability across highly urbanized and suburban areas. Based on the PCA, 38 indicators were defined as the most comprehensive flood vulnerability assessment (FVA) used in Egyptian cities. Additionally, due to reliability of the approach to indicator selection and the weighting process, the chosen 13 indicators for the AHP analysis yielded similar results. This research provides spatial planners and decision-makers with an integrated, comprehensive, and unified urban FVI to assess vulnerability and, thus, improve flood resilience in Egypt and countries in similar situations.

Automated summary

Several cities are highly vulnerable to floods due to urbanization, population growth, and climate change. The development of an integrated flood vulnerability index (FVI) is important for identifying weaknesses, monitoring changes, and supporting targeted flood risk adaptation policies. This study focuses on developing an urban FVI for Alexandria, Egypt, using an indicator-based approach to assess exposure, susceptibility, and resilience to urban flooding at the neighborhood scale.