Comparative evaluation of landslide susceptibility map using Analytical Hierarchy Process (AHP) and Fuzzy methods

Among many natural hazards, landslides are one of the most widespread and destructive. Due to the high mountainous topography, tectonic activity, high seismicity, diverse geological and climatic conditions, basically, Iran has a natural condition for creating a wide range of landslides and these landslides annually cause both life loss and financial damage to the country. Since it is difficult to predict the timing of landslides, identifying susceptible areas to landslides, and zoning these areas based on potential risk are highly important. Therefore landslide-prone areas need to be identified in order to reduce such damage. In this respect, landslide susceptibility assessment can provide valuable information essential for hazard mitigation. The main goal of landslide susceptibility analysis is to identify dangerous and high-risk areas and thus reduce landslide damage through suitable mitigation measures. Since the exact prediction of landslides occurrence isn’t possible by human sciences, thus, we can prevent the damages of this phenomenon by identification of landslide susceptible areas and prioritizing them. Binalood Mountain in Khorasan Razavi Province, Due to its geological location, geomorphology, topography, climate, vegetation, has kinds of mass movement. The results of these studies can be used as fundamental information by environmental managers and planners. Landslide hazard zonation was challenged by several researchers in recent years. In order to provide landslide hazard, zonation maps various methods such as Fuzzy logic, statistic methods and Analytic Hierarchy Process (AHP) can be used. Since the early 1970s, many scientists have attempted to assess landslide hazards and produced hazard zonation maps portraying their spatial distribution by applying many different GIS-based methods. Different models and methods have been proposed to produce Landslide hazard zonation. The aim of this study is to develop and compare detailed landslide susceptibility maps (LSM) for Binalood Mountain, using Fuzzy and AHP methods in the framework of the GIS.

 The study area is the northern and southern slopes of the Binalood Mountains that are located in the Khorasan Razavi Province. The present study area fallows under 36 ° 1' to 36 ° 15' north latitudes and 58° 38' to 59 ° 35' east longitudes. According to Geological, Geomorphologic, Hydrological, Climatic, Human and Environmental characteristics of the study area and using comparative studies and results of other researchers, 20 criteria and sub-criteria were identified to achieve the goals. The needed Layers of landslide hazard zonation were prepared using ArcGIS software. These layers are slope, aspect, altitude classes, geology, distance from the river, river density, distance from the road, road density, distance from the fault, fault density, morphological units, topographic indexes (stream power index (SPI), topographic wetness index (TWI) and slope length index (LS)), geomorphological indexes (topographic position index (TPI), topographic roughness index (TRI) and surface curvature index, land use, isothermal lines, and Rainfall lines. Thun, The landslide inventory map has been created in the study area. Subsequently, landslide susceptibility maps were produced using Fuzzy Logic and Analytical Hierarchy Process (AHP) models. After preparing the layers, the next step was to assign weight values to the raster layers, and to the classes of each layer, respectively. This step was realized with the use of the AHP method. So, the landslide hazard zonation map of the study area was presented using weight exertion of factors in their layers and integration of them by Arc GIS software. In the Fuzzy method, after fuzzyizing the layers in the ArcGIS environment, the landslide risk zoning was performed using fuzzy gamma 0.8. For verification, the receiver operating characteristic (ROC) curves were drawn and the areas under the curve (AUC) were calculated. Finally, the ratio of the percentage of landslides was in each zone to the percentage of the total area of the zone was calculated.

 The results of weighting the parameters affecting the landslide using the Analytic Hierarchy Process (AHP) showed that geological, slope, and fault factors have the greatest impact on the occurrence of landslide risk in the study area, respectively. The class of very high and high susceptibility covers 47.8% of the total area in the landslide susceptibility map generated with the AHP model. Low and moderate susceptible classes make up 13.4 and 38.8% of the total area, respectively. According to the landslide susceptibility map based on the Fuzzy Method, 27.7% of the total area was determined to be very high and high susceptibility to landslide. Low and moderate susceptible classes constitute 56.8%, and 15.5% of the area, respectively. The AUC values were 0.817 and 0.752 for AHP and Fuzzy models and the training accuracy was 81.7 and 75.2%, respectively. It can be concluded that both models utilized in this study showed reasonably good accuracy in predicting the landslide susceptibility of the study area. Finally, the ratio of the percentage of landslides was ineach zone to the percentage of the total area of zone showed the NRi values in each susceptible class for the AHP model more than the Fuzzy method. The larger ratio in the AHP method indicates its better consistency than the Fuzzy method, implying more coverage of landslides in a smaller area by the AHP method. This result represents the better accuracy of the AHP method than the Fuzzy method in the landslide susceptibility map.

In this study, the most widely accepted models, AHP and Fuzzy were used for producing Landslide Susceptibility Map (LSM) and their performances were compared. The LSMs were divided into five landslide susceptibility classes. The performance of the resulting LSMs was verified by the ROC curves and Numerical Ratio (NRi). The results show that the AHP and Fuzzy models are successful estimators. The map produced by the AHP model exhibited a slightly better result for landslide susceptibility mapping in the study area. These two techniques may be characterized by incorporating a wide range of conditioning factors. Also, they can discriminate the causative factors for understanding the importance of each factor. The interpretation of the susceptibility map indicates that geological, slope, and fault play major roles in landslide occurrence and distribution in the study area. The landslide susceptibility maps like the one produced in this study should provide a valuable tool for the use of planners and engineers for reorganizing or planning new programs.