Quantifying the contributions of snowmelt and rainfall to alpine debris flow in the eastern Tibetan Plateau using Sentinel-2 satellite imagery and hydrological simulation

Study region The Ridi Gully watershed, a typical alpine catchment on the eastern Tibetan Plateau, China, focusing on the catastrophic debris flow event on 3 August 2024. Study focus Accurate quantitative partitioning of water source contributions to alpine debris flows remains a critical challenge for early warning research. This study combines multi-temporal Sentinel-2 remote sensing interpretation, a temperature-corrected snow cover reconstruction model, and HEC-HMS hydrological modelling. Scenario simulations are adopted to quantify the respective contributions of snowmelt and rainfall to debris flow initiation, supplemented by multi-scenario sensitivity analyses. New hydrological insights for the region Anomalously high 2024 spring-summer temperatures accelerated snow ablation, reducing snow cover area to only 7.66% by 1 August. Snowmelt accounted for 32.63% of total flood volume but less than 1% of peak discharge, while rainfall contributed 67.37% of flood volume and 99.32% of peak discharge. Snowmelt establishes a hydrological background field to lower sediment mobilization thresholds, whereas short-duration high-intensity rainfall is identified as the decisive trigger in our model-based estimates. A dual-factor dynamic early warning strategy is proposed for multi-source alpine debris flow risk mitigation.