Urban flood susceptibility prediction using a Fuzzy-Delphi hybrid model in Sanandaj city

Abstract

Introduction

According to the definition, a flood is an extreme and exceptional flow, although every exceptional flow will not turn into a destructive flood, but different factors must be changed in nature to cause destruction, damage, and casualties. The increase in the occurrence and frequency of floods has a direct relationship with technological progress and irrationality in land occupation. In general, floods can be divided into four groups include flash floods, river floods, urban floods, and coastal floods. Urban floods usually cause fewer casualties and mainly create damage caused by flooding, disruption of traffic, interruption in socio-economic activities, and problems of this kind. While the damage caused by non-urban floods is often heavy and sometimes accompanied by high and catastrophic casualties. According to the Mediterranean climate, Iran is the seventh country in the world in terms of flooding. The area of flood-prone areas of the country is estimated to be around 91 million hectares. In other words, 55% of the country's surface has contributed to the production of surface runoff, of which about 42 million hectares have moderate to very high flood intensity. Ahmadi et al. (2023) carried out flood susceptibility of Sanandaj city with a fuzzy method. They used 6 effective factors including slope angle, elevation, curvature, drainage density, land use, and distance from waterways. The results showed that the factor of distance from the waterway and the density of the waterway, respectively, had the greatest effect on the occurrence of urban floods. Although the review of sources shows the development of knowledge-based methods, statistical methods, and artificial intelligence algorithms in predicting flood-prone areas in urban and non-urban watersheds in different regions of the world. However, a method in which a combination of the Fuzzy, Delphi, and Analytic Hierarchy Process (FDAHP) in urban flood susceptibility has not been done so far. Therefore, according to the importance of the issue and raising a question, what are the most important factors in the occurrence of floods? And is it possible to determine flood-prone areas in urban areas by the FDAHP hybrid model? The purpose of this research is to identify the factors influencing the occurrence of floods and predict flood-prone areas in Sanandaj City. Identifying the areas where floods have occurred is very important for verifying the final urban flood map. For this purpose, the experts, as well as local interviews and field surveys in Sanandaj city, were used to identify these areas. Based on this, 37 points were identified and recorded by the Global Positioning System (GPS).

Materials and Methods

In the current research, which has a descriptive-analytical-comparative approach, in order to predict floods in Sanandaj city, the FDAHP was used. First, each of the variables (14 variables) was scored by flood experts and completed using the scores obtained from other stages of the FDAHP model. After collecting the opinions, finally, the relative weights of the indicators were determined using the hybrid model, and finally, the flood prediction map of Sanandaj city was prepared using ArcGIS 10.7 software. Most of the urban floods are close to areas with high residential density and waterways that have been cut due to urban construction.

Results and Discussion

Table 2 showed that slopes of less than 10% (flat), areas with an elevation of less than 1400 meters, flat aspect, urban land use with building density, rainfall more than 369 mm, and lithology type Qt2 had the highest susceptibility to the occurrence of floods compared to other classifications of the factors in Sanandaj city. Based on Figure 3, the results indicated that the density of the waterway, the slope angle, and the distance from the waterway had the highest influence on the occurrence of floods. Rainfall, road density, building density, distance from residential areas, distance from roads, flow accumulation, elevation, land use, lithology, and slope curvature are the next priorities in terms of importance in the occurrence of floods. These results were consistent with the results of Azad Talab et al. (2019) who stated that building density had an important influence on the occurrence of floods in Sanandaj city. Also, the obtained results were in good agreement with the results of Ahmadi et al. (2023), who showed that the distance from the waterway and the density of the waterway are the most important factors affecting the occurrence of urban floods.

Conclusion

As the distance from the city center and residential areas increases, the potential for flooding decreases. The finding revealed that most areas of the studied area were located in medium and high susceptibility classes, which indicated the high potential of flooding in most areas of Sanandaj city. Finally, it can be concluded that obtaining an accurate and reasonable urban flood susceptibility prediction map can help managers and urban planners in identifying flood-prone areas in order to manage the crisis of susceptible areas in the city. Based on the results obtained from the FDAHP hybrid model, this model has a good ability to estimate the areas prone to urban flooding and can be tested and evaluated as a tool to identify this natural hazard in other areas.