Long-term effects of human engineering disturbances on the increase in the excess sediment supply and debris flow...

Intense human engineering activities can trigger a large amounts of loose debris. Subsequently, rainfall enhances sediment transfer from hillslopes to channels, inducing a series of cascading hazards. To better understand the chain effects of human engineering disturbances on the increase in excess sediment supply and debris flow activity, long-term human engineering disturbances were analysed by defining a human engineering disturbance intensity index (HEDI), thereby evaluating the effects of human engineering disturbances on excess sediment supply and debris flow activity. We tracked human engineering disturbances via remote sensing images from 2012 to 2024. The length of newly constructed roads in the study area increased by 231.26% within 12 years, causing a gradual increase in human engineering disturbance intensity over time in an exponential pattern. Long-term human engineering disturbances pose an exponential impact on the increase in the excess sediment supply. Human engineering activities increased debris flow activity in many subbasins between 2012 and 2024, and approximately 36% of subbasins were dominated by high and extreme levels of debris flow activity in recent years. These findings provide crucial implications for understanding the dynamic effects of human engineering activities on debris flow hazards and for modelling the subsequent evolution of geohazards across multiple temporal scales.