Rainfall threshold for the initiation of landslide in Palpa District, West-Central Nepal

Abstract

Landslides are a major hazard in the Lesser Himalaya due to fragile geology, steep slopes, and intense monsoon rainfall. This study, carried out in Palpa District of west-central Nepal, aimed to develop a rainfall threshold for landslide initiation. A landslide inventory and rainfall dataset were analyzed, and the intensity–duration (I–D) method was applied to establish a reliable threshold.

The final equation, I = 58.67 D⁻⁰·⁸⁴, defines the lower limit of rainfall conditions capable of triggering slope failures. Based on this curve, about 97 mm of daily rainfall is sufficient to initiate landslides in Palpa. The threshold shows that both short, intense storms and long-duration moderate rainfall can cause slope failures. The rainfall pattern clearly shows its effect in the maximum number of landslides in the study area. Along with this, the study also shows that geology, soil type and human activities like farming and road construction also have major influence in slope stability. Comparison with global and regional curves indicates that the Palpa threshold is higher than global baselines but slightly lower than those from other parts of Nepal and India, reflecting the district’s unique geology and rainfall pattern.

The findings provide a practical basis for landslide early warning systems and highlight the role of both natural and human factors in slope instability