Rainfall threshold for landslide awareness – Focusing on the case study in the landslide EVO pilot area region in western Nepal

Abstract

Nepal’s rugged topography, unstable young geological formations, and fragile rocks make the country highly vulnerable to water-induced hazards such as landslides, soil erosion, and debris torrents. Hilly watersheds and settlements in hills and river banks are naturally vulnerable during heavy rainfall. The landslide EVO project selected two landslide areas, one the Bajedi landslides in the Bajura district, and another Sunkuda landslides in Bajhang district of Nepal. Automatic rain gauges were installed, and data were recorded for 2019 and 2021. The best-fit trend lines are determined by the observed rainfall depths of different durations. In addition, 24-hour rainfall records and landslide events that occurred in the region outside the pilot areas in the year 2019 were also analyzed and correlated. Rainfall intensities and depths corresponding to maximum, minimum, and average depth are correlated for different durations. The correlation between rainfall depths and durations data showed an excellent fitting observed. The trend line is considered as the rainfall threshold line for landslide risk assessment for the region.