A quantitative debris-flow risk modelling framework for pipeline infrastructure in tropical mountainous catchments

Abstract Debris flows are highly destructive geomorphological processes in mountainous regions because of their high mobility, sediment transport capacity, and impact potential, posing a significant threat to human settlements and critical infrastructure. However, their effects on linear energy infrastructure, such as pipelines, remain poorly addressed in quantitative risk assessment frameworks. This study proposes the Debris-Flow Infrastructure Risk Index (DFIRI), a quantitative framework designed to assess the relative impact potential of debris flows at pipeline crossings in tropical mountainous catchments. The framework integrates geomorphological susceptibility at the catchment scale, hazard intensity derived from numerical modeling using the RAMMS-DF model, and a structural exposure proxy based on pipeline construction typologies, enabling consistent comparisons across infrastructure segments. The methodology was applied to eight catchments in the Serra do Mar region of southeastern Brazil, encompassing the municipalities of Cubatão and São Sebastião. The results demonstrate pronounced spatial variability in debris-flow intensity, with hazard intensity reaching high relative values (H i up to 0.95) in Cubatão while remaining substantially lower in São Sebastião (H i ≤ 0.21 at the analyzed crossings). Crossings characterized by greater structural exposure, particularly aerial configurations, consistently exhibited higher DFIRI values, indicating greater potential for impact under comparable hazard conditions. The proposed framework enables the systematic identification of critical pipeline segments and provides a consistent basis for prioritizing mitigation and monitoring strategies. By integrating process-based modeling with infrastructure-specific exposure conditions, the DFIRI advances current approaches to debris-flow impact assessment and provides a reproducible tool for decision-making in mountainous environments.