Long-term, national-scale records of landslide persistence and dynamic hazard in a mountain landscape

Abstract As mountain populations grow and exposure to hazard increases, understanding the dynamic hazard posed by landslides is essential. However, our ability to constrain landslide hazard is limited by relatively few good-quality datasets that are often collected across small geographical areas. These datasets typically focus on specific triggering events, such as earthquakes or rainstorms, further complicating assessments of landslide hazard through time. To better capture landslide hazard through space and time, long-term datasets over large extents are needed. Here, we analyse a 22-year record of landslide occurrence to decipher the dynamic nature of the hazard posed by landslides in Nepal. We find that recurrent or persistent landslides dominate national-scale patterns of landsliding, accounting for c. 80% of all visible landslides at any given point in time. Of new landslide areas, only half occurred in locations >30 m away from other landslides. These findings emphasise the importance of also considering pre-existing landslides when assessing hazard. Individual triggering events, including both earthquakes and rainfall, leave a distinctive footprint visible at the national scale in metrics such as landslide density, persistence, and recurrence. Such metrics add significant value to multi-temporal landslide inventories and provide a basis for mitigation efforts, particularly where resources are limited.