Flood risk assessment under non-stationary conditions using gis-based multi-criteria decision-making approaches

Floods are one of the major natural disasters causing significant economic losses and serious risks to life safety. Therefore, flood risk assessment studies in urban areas are crucial for flood mitigation and the implementation of sustainable development activities. Although studies on flood risk have increased, research examining the effects of rainfall at different return periods under non-stationary conditions on flood risk is insufficient in Geographic Information System (GIS) and multi-criteria decision-making model (MCDM) based flood risk assessments. To address this gap, the proposed thesis integrates rainfall quantiles calculated for different return periods under non-stationary conditions with MCDM-based flood hazard mapping techniques to identify and prioritize flood risk areas in Izmir, one of Turkey's most populous cities. In this study, the Analytical Hierarchy Process (AHP) was first integrated into the GIS to assess the existing flood risk, and the VIseKriterijumsa Optimizacija I Kompromisno Resenje (VIKOR) approach was used to analyze the flood risk priority of 165 critically identified points. According to the assessment results, the districts of Buca, Menderes, Bornova, Kemalpaşa, Çeşme, Torbalı, Menemen, Seferihisar, and Çiğli are under high flood risk. VIKOR results show that the highest flood risk points are R91 (Çeşme), R153 (Buca), and R93 (Çeşme). To conduct a comprehensive risk assessment in the study area, rainfall estimates obtained the Generalized Additive Models for Location, Scale and Shape (GAMLSS) at 10, 20, 50, and 100-year return levels under non-stationary conditions were re-weighted with AHP and included in the hazard criteria, and flood risk analyses were performed for four scenarios. The results showed that as return periods increased, high-risk areas expanded, while low-risk areas contracted. Unlike previous findings, the VIKOR results revealed that points R55, R56, and R54 in Kemalpaşa district had the highest flood risk in all four scenarios. It is believed that the proposed integrated approach will provide important information to decision-makers regarding flood risk reduction strategies in İzmir province.