Spatial distribution and changes in the debris flow hazard across High Mountain Asia

Debris flows and floods and flash floods pose hazards to the densely populated areas of High Mountain Asia (HMA). The continuous decline in the cryosphere across the region such as glacier mass loss and permafrost thaw leads to exposure of the unconsolidated debris material and sediment deposits. This has led to changes in the magnitude and frequency of debris flows and floods. We aim to identify the controlling parameters and quantify the likelihood of debris flow and floods and the change in likelihood due to projected regional climate and cryosphere changes. Based on visual inspection of alluvial deposition and surface properties of the alluvial fans, we identified catchments across HMA where floods or debris flows occur. We built a database with morphometrical (e.g. catchment area, perimeter, slope, elevation range, Melton ratio) and climatic features (e.g. temperature and precipitation regime, freeze – thaw cycles, glacier and permafrost area) and build a CatBoost gradient boosting based machine learning classifier. We identify that debris flows are more likely to occur in small catchments, defined as catchments with small Melton ratio and high slope. Projected regional climate change will decrease the probability of the debris flows. It will also increase the probability of the flood being a dominant process in the catchment across the entire HMA.