Assessment of Sediment-Related Disasters in Snowmelt Season Under Climate Change

Snowmelt-season sediment hazards in cold regions are becoming increasingly complex under climate change, as rising air temperatures and rainfall-on-snow events enhance interactions between snow, meltwater, and sediment. Compound processes may generate hazard magnitudes that are inadequately captured when avalanches and debris flows are assessed independently. This study develops a first-order framework for assessing snowmelt-season sediment hazards, using the 2018 Nozuka Tunnel disaster in Hokkaido, Japan, as a case study. Numerical simulations for the three scenarios (avalanche flow, debris flow, and snow–sediment mixed flow) were conducted under identical topographic and numerical conditions to evaluate the influence of snow–sediment interactions on the flow behavior, affected area, and deposition characteristics. Key initiation and material parameters were constrained via inverse analysis (parameter-search calibration) using the observed deposition extent, and Sentinel-1 SAR-derived surface change areas were used as independent spatial information to assess the plausibility and spatial consistency of the simulated deposition footprint. Future hazard amplification was examined using projected climate conditions. The snow–sediment mixed-flow scenario produces larger affected areas and deposition volumes than simulations that treat avalanche- or debris flow processes independently, and its simulated deposition extent is spatially consistent with SAR imagery. Future hazards may be amplified under warmer and wetter conditions. The proposed framework integrates disaster records, topographic analysis, validated snow–sediment mixed-flow simulations, and impact-area estimations to support hazard assessment and disaster mitigation in snow-dominated cold regions. These insights support climate-adaptive, sustainable infrastructure risk management in snow-dominated cold regions.