Quantitative assessment of expected direct economic losses of buildings for debris flows in multiple rainfall intensity scenarios in Yangling Gully, Southwest China

The potential risks associated with debris flows have significantly increased due to changes in global climate, population growth, and economic development. Despite the high susceptibility of debris flows in the Wenchuan earthquake-affected area, few studies have focused on quantitative risk assessment methods for debris flows. To overcome this shortcoming, we proposed an integrated approach by using a probability-based model and numerical simulations to quantify the expected direct economic losses of buildings for debris flows under multiple rainfall intensity scenarios. First, we simulated the hazard processes of debris flows with recurrence periods of 20, 50, 100, and 200 years and obtained the distribution of debris flow intensities defined by the momentum flux. Then, we assessed the direct economic losses for each building related to different recurrence periods based on fragility curves and debris flow intensity maps. The results show that the risk loss of different hazard scenarios increases dramatically with an increase in debris flow magnitude. This methodology provides visual and quantitative risk assessment for specific buildings affected by debris flows, enabling authorities and decision-makers to reduce risk and optimize risk management strategies. It is a rapid and effective way to assess the capacity of the built environment to resist the risk of debris flows in the Wenchuan earthquake-affected areas.