Philippines - Quantitative Lahar Impact and Loss Assessment under changing Land Use and Climate Scenarios

Lahars are volcanic mudflows that often occur during and after volcanic eruptions when ash deposited from the volcano is remobilized by rainfall. Lahars are a major hazard to people, often resulting in fatalities and displacement of communities. Lahars are a particular hazard in the Philippines due to the large number of volcanoes that erupt explosively and the tropical climate.

The aim of this proposal is to develop an integrated, coherent model of lahars from their generation in catchments on volcanic flanks to their impacts on the build environment. This study has been co-developed between the University of Bristol and the Philippines Institute of Volcanology and Seismology (PHIVOLCS) during an active volcanic crisis in the Philippines, with Mt Mayon erupting and producing lahars. The project will advance lahar hazard assessment through the development of susceptibility and impact mapping, where the impacts are inferred from a convolution of predictions of lahar inundation and damage. The proposal will develop a new collaboration between UK and Philippines partners, based on combining expertise in hydrological and hazard modelling, sedimentology, geomorphology and hydrogeology.

Our study will develop new and apply new models for the hydrology of catchments with recent ash deposits, informed by field studies of these environments conducted in the Philippines. This will allow rainfall forecasts to be propagated into lahar source conditions, including under future climate and land use settings. The catchment hydrology will be linked to a model of lahar motion, to allow the assessment of lahar inundation and the physical impacts in urban areas further from the volcano. We will apply the dynamic model at high resolution to provide predictions of lahar motion on the building scale. New mathematical modelling on the impacts of lahars on structure will provide methodology for assessing the physical vulnerability of the build environment to lahars. This integrated approach will allow, for the first time, a comprehensive assessment of the lahar hazards across a range of scales, providing the basis of future quantification of lahar risk, and will support the design of early warning systems.

The project will provide advances in capacity for lahar hazard assessment in the Philippines and in other tropical countries with active volcanoes, and in dynamic aspects of risk related to hydrometeorological hazards, climate change, urbanization and land use change. Case study locations have been chosen to provide a combination of changing exposure due to climate and land use changes, and in rural and peri-urban settings.

Lahars are a major volcanic hazard, accounting for 15% of fatalities related to volcanoes, disruption to lives and livelihoods, and substantial economic costs for mitigation, response, recovery and repair operations. The Philippines experience many lahars due to the large number of active volcanoes and the tropical climate. This project, which has been co-developed by the University of Bristol and the Philippines Institute of Volcanology and Seismology (PHIVOLCS), will address lahar hazards in the Philippines with a focus on integrating modelling approaches so that the physical vulnerability of the built environment can be assessed quantitatively. This is a crucial component of quantitative risk analysis, recognized as an important stage of disaster risk reduction.

PHIVOLCS have a mandate to monitor the volcanoes in the Philippines and assess the related hazards. The co-development of this project will ensure that the results are directly and immediately beneficial to communities in the Philippines through PHIVOLCS. Our scientific developments will be demonstrated by application at two case-study volcanoes where the lahar risk is elevated: Mt Pinatubo, where lahar activity persists long after an eruption (illustrating the long duration of lahar activity), and Mt Mayon which is currently erupting and producing lahars impacting nearby communities. Additionally, we will engage with other agencies and organizations in the Philippines concerned with lahar hazards throughout the project to ensure our studies meet their needs, particularly during periods of active volcanic activity. Further national, regional and international dissemination and knowledge sharing will be achieved through an international workshop in the Philippines and a training workshop offered as part of a conference series in international volcanic hazards.

Enhancing the uptake of modelling in hazard assessment is an essential part of improving hazard prediction and risk reduction. Our models will be developed into easy-to-use tools, provided freely through online interfaces with supporting training materials. Our current model, LaharFlow, has a growing international user community (including ODA countries Ecuador, Colombia, Peru and Chile). LaharFlow will be developed and enhanced to incorporate our integrated modelling methodology, providing the ability for meteorological forecasts to be propagated to a quantitative lahar hazard footprint and vulnerability assessment for impacted areas.

Our scientific advances are also beneficial to the insurance industry and will allow lahar risk analyses to be conducted using loss modelling methodologies that are well established for other natural hazards, notably flood risk. To ensure these benefits are realized, we will engage with the insurance industry, facilitated by our partnership with Oasis, and will develop our model to be integrated into the Oasis Loss Modelling Framework, providing free access to sophisticated loss modelling tools. Further dissemination of the application of our methodological framework to quantitative risk analyses will be achieved through the creation of comprehensive reports based on our case-studies and submitted for inclusion in international risk catalogues.

Our case studies in the Philippines will highlight the advantages of our integrated modelling approach. We will engage with the broad scientific community concerned with natural hazards to ensure that our methodology and results can be exploited widely. This is particularly important for our study modelling physical vulnerability to flows; the vulnerability aspect of risk analysis Is comparatively poorly established. Our modelling framework for flow impacts on the building scale can be applied to other hazards (such as debris flows and hyperconcentrated flash floods). We will disseminate our advances to the research communities through international multidisciplinary conferences and in cross-disciplinary journals.