Migration patterns of source materials and their potential indication for debris flow initiation in Wenchuan seismic area

The occurrence of debris flows is contingent upon the synergistic influence of the distribution and volume of loose source materials and rainfall intensity, particularly in seismic areas where sediment has undergone long-term evolution and migration. Unfortunately, conventional monitoring and warning methods neglect the effect of sediment migration on debris flow generation due to their inherent constraints in capturing long-term and sustained sediment evolution across the entire catchment. In this study, we propose an innovative utilization of small baseline interferometric synthetic aperture radar (SBAS-InSAR) technology as a promising solution for investigating sediment migration patterns prior to debris flows, which offers long-term continuous monitoring at the catchment scale. Unlike temporary monitoring, this study provides valuable insights into the long-term dynamics of sediment by analyzing the erosion and deposition processes within a seismic catchment. It not only uncovers the persistent transition of bank sediment into channel sediment over several years following the earthquake but also identifies the presence of sustained erosion in the channel sediment prior to the initiation of debris flows. On the basis of the time series analysis, this study establishes the correlation between the pre-disaster indication of sediment mobilization and debris flow initiation, which emphasizes its significance in developing a method that possesses prolonged early warning capabilities for predicting the occurrence of debris flows. In conclusion, SBAS-InSAR is an effective approach for monitoring all-weather sediment evolution at large spatiotemporal scales, which contributes to the enhancement in debris flow early warning systems and the protection of human lives and properties.