Objective: Landslides are one of the types of environmental hazards that cause extensive damage in many watersheds annually. The main objective of this research is to evaluate landslide susceptibility using fuzzy set theory, fuzzy operators, and landslide zoning in the Sarjoo watershed of Ilam
Methods: One of the scientifically accurate methods for investigating landslide risk is the use of fuzzy logic. A geographic information system (GIS) was used to prepare a database of factors affecting landslides in the region and determine landslide zones. The weight of each class of factors between 0 and 1 was calculated and weight maps were prepared using the fuzzy method. The weight maps were combined using the fuzzy operator method. Landslide susceptibility zoning in the selected watershed was carried out using fuzzy logic theory including algebraic addition, algebraic multiplication, and fuzzy gamma.The results obtained were evaluated using the compression ratio (Dr) and qualitative sum (Qs) indices.
Results: The results obtained from the fuzzy algebraic sum operator in the form of a landslide susceptibility map in the Sarjui watershed are about 99% in high and very high risk zones. While the results obtained from the fuzzy algebraic multiplication operator indicate that 87% of the watershed is in medium to high risk zones.
Conclusions: In this study, the gamma model of 0.4 and 0.1 are the most appropriate methods. On the other hand, the results showed that the fuzzy algebraic sum method in the Sarjui watershed with values of 0.4918 is not suitable for investigating landslides.