## 8 Conclusions  
A representative landslide area was chosen in Bartin, one of the cities where rainfall-induced landslides are most common in the Western Black Sea Region of Turkiye. A detailed field monitoring program was conducted to clarify the triggering mechanisms of rainfall-induced landslides. The instrumentation covered the measurements of site suction, volumetric water content, groundwater level, and rainfall amount over a period of two years. Various stability analyses were performed regarding both pore pressures after transient flow infiltration and site-measured sections. Rainfall thresholds for landslideswere obtained by considering the site-specific seasonal suctions, groundwater levels, and saturated/unsaturated hydro-mechanical properties. The achievements obtained from this study, which were planned to illuminate the hydro-mechanical behavior of rainfall-induced landslides in the region and to contribute to landslide early warning systems in this sense, are given below. In-situ monitoring of volumetric water content, matric suction and groundwater level depending on seasonal conditions for two years has importance in terms of establishing site-specific initial conditions and stability. According to the measurements in the field, it can be remarked that the first five months of the year are wet, and the other months are dry. It has been observed that wet period conditions create more critical situations for failure compared to dry period conditions, so the potential for landslides is higher for wet periods. From the stability analyses based on the measured average pore pressures for dry and wet seasons, the factor of safety was calculated as 1.74 and 1.32, respectively. The results are significant as they reveal how stability is affected by the seasonal changes in suction and positive pore-water pressure in the region. It has been observed in the studies that the seasonal initial conditions, rainfall intensity, duration, and range of possible saturated hydraulic conductivities affect the stability in various ways. Transient flow infiltration analyses showed that the groundwater level could rise to the ground surface after possible rainfalls for the area, and the matric suction could be lost completely. The factor of safety might drop below the limit equilibrium condition (F.S = 1). Rainfall thresholds for landslides were established as a result of numerical analyses performed, considering measured seasonal suctions, groundwater level changes and saturated/unsaturated hydro-mechanical properties. In the analyses, rainfall thresholds were ascertained by investigating the rainfall intensities and duration, which creates a factor of safety 1.50 and 1.02 (the lowest factor of safety reached in the numerical analyses) for the dry period conditions, and 1.00 (limit equilibrium state) for the wet period. Established models were validated by instrumental monitoring and past landslide data observed in the region. Based on an interpretation of analyses, the saturated hydraulic conductivities in the studied area are expected to be between 1.76 \(\times\) 10\({}^{-6}\) m/s and 1.76 \(\times\) 10\({}^{-7}\) m/s. In this case, landslide-risk conditions are reached if rainfall of over 10 mm/h for dry periods lasts between 0.85 h and 8.37 h for an FoS = 1.5 and 1.67 h-17 h for an FoS = 1.0 depending on the saturated hydraulic conductivity. When rainfall intensities are lower than 10 mm/h, longer rainfall durations are required for a landslide to occur. For wet periods, landslide-risk situations are reached when rainfall is over 1 mm/h and lasts between 0.36 h and 3.67 h, depending on the permeability. Conceptualization, S.A., T.T. and Y.Y. ; methodology, S.A., T.T. and Y.Y. ; software, S.A.; validation, S.A. and T.T. ; formal analysis, S.A.; investigation, S.A.; resources, S.A.; data curation, S.A. and T.T. ; writing--original draft preparation, S.A.; writing--review and editing, S.A., T.T. and Y.Y; visualization, S.A.; supervision, T.T. and Y.Y. ; project administration, S.A. and Y.Y.