The orographic influence on storm variability, extreme rainfall characteristics and rainfall-triggered landsliding in the central Nepalese Himalaya

Abstract

Variation in extreme rainfall under the influence of orography plays an important yet poorly understood role in the erosion of mountains. In the steep terrain of the Himalaya, intense precipitation frequently triggers soil and shallow bedrock landslides during the summer monsoon. Characterizing monsoon-triggered landsliding as a dominant erosion process and hazard requires an understanding of the intensity and duration of precipitation during storms, but the daily resolution and sparse spatial coverage of local precipitation instrumental records are insufficient. Here we use NASA’s Global Precipitation Measurement (GPM) IMERG 30-minute, 0.1x0.1 degree product scaled to match local rain gauge records to characterize extreme rainfall events (EREs) over a study area in central Nepal. We separate extreme events in the time series with a minimum dry period between storm arrivals and cluster them using a K-means multivariate approach. Results show variability in the intensity and duration of EREs with distance from the Himalayan range front in a pattern consistent with the orographic effect also observed on total precipitation volume. Storms of highest intensity and shortest duration are coincident with increased density in monsoon-driven landsliding.