Multi-hazard probability assessment in Quinali A Watershed, Albay, Philippines

The Quinali A Watershed, Philippines experiences the compounded effects of interconnected multi-hazard events and there remain significant gaps in understanding the spatial variability of these multi-hazard occurrences within the watershed. To better understand their potential impacts on communities within the watershed, we examine the spatial distribution of multi-hazard events, focusing on four hazards: flood, rain-induced landslide, liquefaction, and pyroclastic flow hazards. Individual hazard maps were created utilizing various numerical modeling techniques, and linear aggregation was employed through an analytic hierarchy process to develop a comprehensive multi-hazard map. Our results show that approximately 60 % of the watershed can be affected by multi-hazard events with high multi-hazard levels widespread along areas of low topographic relief in the watershed floodplains and the foot slopes of the southwestern section of Mayon Volcano. The analysis further confirmed that high levels of multi-hazard risk are found in locations where the individual hazard levels are already significant and where multiple hazard layers overlap. Presently, initiatives aimed to integrate climate and disaster risk assessments into local planning predominantly concentrate on the effects of single hazards. This study illustrates the necessity of a fundamental comprehension of the compounding effects of various hazards and their integration into disaster risk assessments to improve disaster management strategies. This approach is consistent with the UNDRR's recommendations to enhance the implementation of Multi-Hazard Early Warning Systems (MHEWS) across all sectors, thereby safeguarding the most exposed populations from natural hazards.