## 1 Introduction  
[PERSON] & [PERSON] [1] define a landslide as \"the downslope movement of soil or rock material under the influence of gravity\". Heavy rains, deforestation, and land use are factors that can accelerate landslides. Deforestation for instance can weaken the integrity of the topsoil and reduce slope strength leading to landslides. The most important factor contributing to landslides is arguably the slope angle [1]. The slope angle is directly proportional to the shear stress in the soil or any unconsolidated material. This means that, if the slope angle increases, the shear stress within the material increases, thereby initiating a landslide. Human factors contribute to landslides through the weakening of slope soil structures, reducing slope strength, and increasing stress placed upon it. A simple example can be through \"reducing friction on slopes\", \"adding weight to slopes\", \"reducing the resisting mass\", and \"making the angle of the slope steeper\" [2]. All these factors can result in landslides if not adequately monitored [1]. Irrigation, clearing of vegetation, digging, etc. reduces the slope strength [1, 3], while slope angle is the most significant component of slope stability analysis [1], and in actual sense the slope angle is directly proportional to the shear stress in soil or any unconsolidated material. Therefore, if the slope angle increases, the shear stress of the material increases. Some recent studies have made it possible to divide and classify landslides based on several factors, including types and speed of movement, failure mechanisms, etc. Almost all reported high or large landslides are associated with predisposing conditions [4; 5; 6; 7; 8; 9; 10; 11]. These include prevailing clay material, the morphological setting of the slope, extreme rainfall events, and human activities such as road construction. Extreme rainfall and snowmelt are however the greatest triggers of the landslides [11]. Nonetheless, understanding of the impact of extreme rainfall on slope stability in unsaturated soil remains to be improved. [PERSON] and [PERSON] [12] have listed rainfall as one of the most common landslides widespread triggering hazards in the world. The previous author [12] supported their arguments by outlining that the hydrology in and around a landslide area is among the factor leading into pore pressure buildup in the soil skeleton, as a result, the shear strength of the soil reduces due \"to the buoyancy force exerted by water in a saturated soil and to soil suction in an unsaturated soil\". Furthermore, previous authors [12] also documented that the \"extraordinary precipitation events trigger most of the landslides, but, at the same time, the vast majority of slopes do not fail\" the previous authors [12] suggestion correlates very well with some studies such as those of [PERSON] and [PERSON] [13], [PERSON] and [PERSON] [14], and [PERSON] [15]. An encouraging study by [PERSON] et al. [16] suggested that rainfall-triggered landslides tended to occur on dip slopes, instead of the windward slopes, pinpointing geological settings to be the most controlling factor of the mass-wasting processes on hillslope scale than the rainfall condition. This study appears to support or complement one of the suggestions documented by [PERSON] and [PERSON] [13]. Indeed, studies such as those of [PERSON] et al. [17] have validated that geological features such as faults, which are seismic active. Sophisticated methods such as numerical simulated have been implemented to understand the sliding of clay soil material [PERSON] et al. [18], and revealed that \"the high sensitivity and contributes to an improved understanding of the mechanisms of flow sliding insensitive, altered tephras rich in spheroidal halloysite\". In summary, there are several studies [19; 20; 21] that document the effect of rainfall and other factors on triggering landslides. To this end, this paper aims at evaluating the influence of extreme rainfall on the stability of unsaturated soil slope.