The multi-decadal hazard cascade of a tropical mountain wildfire

Abstract

Climate change is driving wildfires to higher elevations, yet the hazard cascades that follow the burning of pristine tropical mountain ecosystems remain largely unexplored. We present an integrated multi-hazard risk assessment methodology combining quantitative remote sensing with qualitative humanitarian and community data, addressing the challenge of characterising cascading hazards in data-scarce mountain environments. Here, we apply this approach to analyse the long-term cascade following a February 2012 wildfire that burned 31 km² of forest and wetland in Uganda's Rwenzori Mountains National Park. We document ten major floods since 2012, including two debris floods in 2013 and 2020 that affected 200,000 people requiring large-scale humanitarian responses. Post-fire increases in erosion and mass movement have widened the River Nyamwamba sevenfold since 2012, breaching copper-cobalt mine tailings and mobilising an estimated 744,000 tonnes of waste into the river resulting in widespread pollution of the river and floodplains. Slow vegetation recovery at high altitudes and positive feedbacks between hazards have prolonged this high-risk state, demonstrating how hazard interactions compound to sustain elevated risk beyond typical post-fire recovery periods.This study demonstrates how the characterisation of multi-hazard cascades and their interactions enable identification of management entry points in resource-constrained settings. However, challenges remain in multi-hazard risk management across spatial and temporal scales; montane environments globally, especially those without a history of fire, suffer from inadequate monitoring infrastructure and limited understanding of post-fire hazard interactions. The intensity and persistence of the Rwenzori hazard cascade highlights how wildfires in mature, fire-sensitive mountain ecosystems can impose long-lasting risks on downstream communities. We recommend that post-fire risk assessments be triggered at lower thresholds of burn area and severity when fires occur in fire-sensitive mountain ecosystems, and that investment in long-term monitoring be prioritized to capture the full temporal evolution of hazard cascades.