Investigating the impacts of effective factors on Sipey village landslide occurrence (Savadkuh county, Mazandaran province)

A landslide is a type of mass-wasting process that acts on natural and engineered slopes. It is the movement of a mass of rock, debris, or earth down a slope, under the influence of gravity (Cruden and Varnes, ۱۹۹۶). Landslides constitute one of the most hazardous geomorphic processes in mountainous areas, which can result in serious injuries, human casualties, and cause environmental and economic damage every year (Fell et al., ۲۰۰۸). Iran, having vast mountainous areas, high tectonic and seismic activity, diverse geological and climatic conditions, has most of the natural conditions for creating a wide range of landslides. Also, due to the lack of comprehensive management and non-compliance with environmental thresholds, it is considered a high-risk country, so it is regarded as one of the ۱۰ most high-risk countries in the world (Davari Sarem et al., ۲۰۲۲). For this reason, most towns and villages in mountainous and steep parts of the country's north are prone to landslides. Depending on the intensity and magnitude of the secondary driving factor (deforestation, road construction, development of cities and villages, intensity and durability of rainfall, earthquake, and other driving factors), the size of landslides that occur in these susceptible lands can be different. In the meantime, rainfall and land use and land cover (LULC) are the most important in such areas. However, little is known about the relationship between these factors with slope instability and landslide occurrences. LULC, as well as its geographical and temporal variations, are known to influence landslide occurrences. They act as landslide predisposing factors, contributing to the control of landslide hazards, and affect the distribution of the vulnerable elements, contributing to determining landslide risk. While most of the geological and geomorphological factors change in relatively long periods, LULC is a highly dynamic factor that may change in a short time due to natural and anthropogenic actions. Changes in LULC, including urbanization in hazardous areas, abandonment of rural and mountain areas, agricultural and forest practices, irrigation, deforestation, and afforestation, affect the distribution, abundance, and activity of landslides. The impact of the changes can be exacerbated or reduced by concurrent variations in the precipitation regimes, foreseen under the effects of the changing climate. Human activities play a major role in LULC changes and related consequences of slope stability. For example, an increase in shallow landslides can be associated with accelerated deforestation (Glade, ۲۰۰۳; Beguería, ۲۰۰۶). Also, rainfall is the most important factor triggering landslides in mountainous and steep areas, so the number of landslidesoften increases after intense and continuous rainfall. Landslides induced by rainfall are caused due to the saturation of the slope and as a result of the reduction of the capillary force in the soil and the increase of the pore water pressure in the slope materials (the result of all of which is the reduction of the shear strength of the materials). The sensitivity of landslides to climate change may depend on their type, especially on the size and depth of the landslide (Crozier, ۲۰۱۰). As shallow landslides are generally governed by shorter-duration rainfall, they may be more influenced by the evolution of parameters in the short-term parameter evolution, such as changes in the intensity of rainfall. Davari Sarem et al., ۲۰۲۱, after studying engineering geological characteristics and stability analysis of the Sipey landslide, concluded that poor quality of slope materials, long-term rainfall, and LULC change due to construction and deforestation have been the most important factors in landslide occurrence and played an important role in the reduction of the safety factor of this slope. In this regard, the present study investigates the quantitative relationship between three factors of rainfall, LULC, and ground displacement with the occurrence of the Sipey landslide. Investigating this landslide as an example of similar landslides that have the potential to occur in this region can be an experience to better understand the factors that could be a serious risk to the region in the future. The innovation of this paper compared to similar research is the use of a comparative perspective so that quantitative calculations are adapted to Sentinel-۱ radar satellite images that show ground realities.