Building risk amplification effect under loess landslides-hydraulic erosion-debris flow cascade in China

The high water sensitivity of loess in the region of northwest China makes it prone to experiencing the Landslides-Hydraulic Erosion-Debris Flow Cascade (LS-HE-DC). The abundance of sediment in LS-HE-DC during the debris flow phase significantly impacts on buildings. The surge in provenance supply during the initiation and evolution of LS-HE-DC mainly amplifies the associated risks. However, the clustering of landslides within LS-HE-DC complicates the understanding of how landslide provenances contribute to debris flow movement and subsequent risk changes. The Eryanggou LS-HE-DC event served as the focal case of this study. By coupling three geological hazard process mechanism models focusing on landslides, hydrology, and debris flow, the volume of landslide provenances involved in debris flow movement was computed to assess the consequential changes in debris flow hazard and the risk of building collapse. The results indicated that the significant amount of provenance generated by landslides was the main reason for the risk expansion. A total of 23 landslides were involved in debris flow movement, providing 2.89*106 m3 of provenances for the final debris flow, resulting in an increase of 63.04% in hazard range, 183 % in average deposition depth, 77.8 % in average velocity and 389 % in average momentum flux at the outlet of the basin. A building collapse would occur when the provenance supply surged by 1.26*106 m3. With an additional 1*105 m3 of provenances, the risk of building collapse would increase by 2.57 %.