Fuzzy set theory and pixel-based landslide risk assessment: the case of Shafe and Baso catchments, Gamo highland, Ethiopia.

Landslide risk assessment is an extension of landslide hazard or susceptibility mapping. It is the most critical component of a landslide hazard reduction plan. The present study was carried out in Shafe and Baso catchments which are found in Gamo high land of Southern Ethiopia and are about 437 km south of Addis Ababa. The areal extent of the present study area is about 284 km². This research was mainly aimed to characterize the landslide risk in the study area for rural population their property and services. In the present research, the landslide risk assessment was made with a major limitation of archived data. In order to overcome the deficiency of landslide data, the danger pixel concept and fuzzy set theory were utilized to evaluate the landslide risk in the study area. In the former approach total number of pixels of different resources that were affected by the landslide hazard in the area was determined. Similarly, the fuzzy set theory, a semi-quantitative method, was used to characterize the risk level of each resource in the study area. This fuzzy linguistic approach has characterized landslide risk in to a matrix form which was further used to determine the landslide risk in the study area. The resource categories that were considered in this research were; settlement, agricultural land, moderate forest, sparse forest, rangeland, bare land, and water body. The risk assessment maps prepared by both methods have delineated different risk zones with more or less similar area coverage. In the landslide risk map, the risk was classified into five classes; very high risk (6.86%), high risk (21.15%), moderate (43.26%), low (10.97%), and very low risk (17.76%). Thus, based on the results, suitable biological and mechanical remedial measures are required to mitigate the landslide hazard in the study area. These measures are particularly required to control the landslide triggering factors such as; gulley erosion, stream erosion, human activities, and groundwater conditions. [ABSTRACT FROM AUTHOR]