Tracing seismic landslide-derived sediment dynamics in response to climate change

Abstract

Mass movements such as landslides are prominent sources of sediment in post-seismic mountain belts. Earthquake triggered landslides can generate substantial volumes of fresh sediment and this may have significant long-term (decade to millennium) geomorphic effects on landscape evolution. Downslope and downstream transport of sediment into the channel network is sensitive to meteorological perturbations especially for extreme rainfall events. However, no established techniques can explicitly fingerprint/track landslide-derived sediment under climate change. In this study, we use a new tracing function incorporated into CAESAR-Lisflood (CL) to track the landslide-derived sediment dynamics in response to climate change. The hourly future rainfall sequences under two climate scenarios (RCP4.5, RCP8.5) were firstly generated using ‘NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP)’ dataset and then used as hydrological input to drive CL simulations. The landscape evolution at the Hongxi basin, which suffered great damage from the Wenchuan earthquake (Ms 8.0), was then simulated for 93 years (2008–2100) using CL under two climate scenarios. The results show that the landslides can greatly increase the sediment yield and climatic perturbations can lead to variation of sediment dynamics, the coupling of these two factors perform a combined impact on sediment budget, while the interplay and relevant importance between landslides and climate impact is dependent on the landslide density of specific basin. The landslide-channel connectivity (location of landslides with respect to river channels) plays an important role in post-earthquake sediment evacuation. The yearly sediment yield generated by the landslides can be stable after 20 years under both RCP 4.5 and RCP 8.5 scenarios in the study basin. These findings are of great importance to understand the interplay between landslide and climatic perturbations and support the risk management and mitigation after the 2008 Wenchuan earthquake.