Landslides are important natural hazard in Turkey especially in Black Sea Region considering the economic damages and life loss. Sinop city enlarge through hillslope areas with its increasing population. The study area is located in Demirciköy Watershed approximately 11 km southwest of Sinop city centre which embodies several landslides. The aim of the work presented in this paper is to propound a new index representing the deterministic part of the landslide susceptibility phenomenon in terms of FSI (factor of safety index) under dynamic soil saturation conditions. SMDR (Soil Moisture Distribution and Routing) model is employed to simulate the dynamic soil saturation variations utilizing with the monthly mean meteorological data. The calculated dynamic factor of safety is transformed to the FSI with the use of a statistical evaluation known as likelihood ratio method. The ultimate landslide susceptibility maps obtained with the new proposed method indicate that deterministic approach produce fairly acceptable results in terms of physical explanation of landslide existence. On the other hand, spatiotemporal evaluation of the landslide susceptibility concept augment the accuracy comparing with the conventional landslide susceptibility concept according to the produced high performance and satisfactory results.