Document Type : Research Paper

Authors

• Ehsan Bazrafshan ¹
• Hossein Malekinezhad ²
• Seyed Zeynalabedin Hosseini ²
• mehdi sepehri ³

¹ Ph.D. Candidate in Watershed Science and Engineering, Department of Rangeland and Watershed Management, Faculty of Natural Resources and Desert Studies, Yazd University, Yazd, Iran

² Associate Professor, Department of Rangeland and Watershed Management, Faculty of Natural Resources and Desert Studies, Yazd University, Yazd, Iran

³ Ph.D. in Watershed Science and Engineering, Rangeland Expert, Research Institute of Forests and Rangelands (RIFR), Iran

Abstract

Introduction
Flood risk management is one of the most significant environmental and developmental challenges in arid and semi-arid regions of Iran. The Fakhraabad watershed in Yazd is prone to sudden floods due to its unique climatic and topographical characteristics, which can result in substantial economic, social, and environmental damages. Since studies related to natural phenomena are often associated with complexity and uncertainty, employing multi-criteria decision-making methods capable of effectively managing these uncertainties can play a key role in improving the analysis and simulation of natural resource-related phenomena. Ultimately, this approach could lead to a reduction in the economic and human costs resulting from these events. Among these methods, the Analytic Hierarchy Process (AHP) has gained a special position due to its simple structure, transparency, and widespread use in natural resource studies and watershed management. This method provides a systematic way of weighting and prioritizing criteria and has offered reliable results in many studies. However, when data or expert judgments are uncertain, the use of complementary approaches can enhance the accuracy of results. In this regard, the IRNAHP method (Fuzzy Analytic Hierarchy Process with Interval Numbers) has a greater ability to model uncertain conditions and can be used as a complement to AHP. Comparing these two methods, while maintaining the position of AHP as a foundational tool, provides a suitable path for selecting a more precise approach in flood risk management.
 
Materials and methods
In this study, to prioritize the sub-basins of the Fakhraabad watershed in Yazd based on flood susceptibility, eight main criteria were used: Digital Elevation Model (DEM), slope, precipitation, fractal dimension, connectivity, Topographic Wetness Index (TWI), Topographic Control Index, and stream power. Data related to these criteria were extracted from hydrological sources, topographic maps, and climatic data, and processed in a Geographic Information System (GIS) environment. To weight and prioritize the criteria, two multi-criteria decision-making methods, AHP and IRNAHP, were applied. In the AHP method, pairwise comparisons were completed with expert opinions, and the relative weights of the criteria were calculated. In the IRNAHP method, fuzzy logic and interval numbers were used to consider the uncertainty in human judgments. The weights obtained from both methods were integrated in the GIS environment to produce flood susceptibility maps of the sub-basins. Finally, to validate the results obtained from the two methods, the output of the SWAT model was used as a reference for comparison to evaluate the accuracy and reliability of each method.
 
Results and discussion
Comparing the results of the two methods with the SWAT model output showed that both AHP and IRNAHP were able to provide an appropriate flood susceptibility zonation pattern. The AHP method, due to its simplicity, transparency, and widespread application in water resource studies, remains a valuable tool. However, as the number of pairwise comparisons increases and expert judgments become more uncertain, the likelihood of uncertainty in the weighting of the indicators also rises. In contrast, the IRNAHP method, utilizing fuzzy logic and interval numbers, was able to better manage this uncertainty and provide more accurate results. Compared to similar studies, the findings of this research also indicated that IRNAHP performed better than AHP in dealing with ambiguous data and environmental complexities.
 
Conclusion
This study compared the two methods, AHP and IRNAHP, for analyzing the flood susceptibility of the sub-basins in the Fakhraabad watershed in Yazd. The results showed that in the AHP method, sub-basins 4, 3, 31, 27, and 29 had the highest flood susceptibility, while sub-basins 15, 22, 14, 21, and 6 showed the lowest susceptibility. In the IRNAHP method, sub-basins 4, 3, 31, 27, and 24 had the highest flood susceptibility, while sub-basins 15, 22, 14, 21, and 12 had the lowest. Due to its simple structure and high interpretability, AHP remains a reliable method for prioritizing criteria. However, when the data or expert opinions contain ambiguity and uncertainty, its accuracy decreases. In contrast, the IRNAHP method, by incorporating fuzzy logic and interval numbers, overcomes this limitation and provides more accurate results. Therefore, it can be concluded that IRNAHP, as a complementary approach to AHP, is a more efficient tool for flood risk management in vulnerable areas.

Keywords

• Analytic Hierarchy Process
• Connectivity
• Flood risk management
• Topographic Wetness Index
• Watershed management