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

Lead Research Organisation: University of Bristol
Department Name: Earth Sciences


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.

Planned Impact

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.


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Bautista M (2023) Quantitative impact assessment of the 2019 tropical cyclone Kammuri lahars: Mayon volcano, Philippines in International Journal of Disaster Risk Reduction

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Hogg A (2021) Dam-break reflection in The Quarterly Journal of Mechanics and Applied Mathematics

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Langham J (2021) Linear stability of shallow morphodynamic flows in Journal of Fluid Mechanics

Description In this project, University of Bristol and Philippines Institute of Volcanology and Seismology (PHIVOLCS) have been working together to build a bespoke hazard assessment tool for lahars (volcanic mudflows) for use in the Philippines, by tackling fundamental research questions for the dynamics of concentrated sediment flows. All the results from the project to date have been co-produced and have arisen from collaborative research bringing together the Philippines team's capabilities in fieldwork and risk science and management, with the UK team's capabilities in modelling hydrological processes and hazardous flows.

The project has achieved significant advances in our capability to model lahars and assess their impacts and associated risk. Novel modelling activities in this project include: (1) the coupling of a dynamic flow model (LaharFlow; with a catchment hydrology model (DECIPHeR; to provide an end-to-end quantitative description of lahar hazard from initiating rainfall to downstream inundation and impacts; (2) the implementation of spatially varying erosion resulting from lahar flow over different land cover types and an assessment of its important for flow dynamics; (3) investigation of the mathematical stability of geological mass movement models that incorporate morphodynamics (coupled flow and modification of the underlying topography by erosion and deposition). The new modelling is being used operationally in the Philippines by PHIVOLCS and is being incorporated into the Philippines national risk assessment system (REDAS;

We coupled the DECIPHeR and LaharFlow models together to assess the impacts of lahars on the Mayon volcano catchments. There were insufficient rain and river gauging stations to allow application of DECIPHeR as previously for UK flood catchments, but we developed a novel approach using satellite-derived rainfall data and calibrated the coupled Decipher-LaharFlow models for the 2019 Typhoon Tisoy lahars around Mayon Volcano. Our calibration accounted for high uncertainty in DECIPHeR outputs (due to lack of constraining gauging data) as well as reasonable ranges for the LaharFlow model parameters. The coupled model was in good agreement with routing and inundation observations from the Tisoy lahars, and was presented at the Water Security and Climate Change conference in Hanoi in 2021. Our studies indicated that the current hydrological model inputs can provide valuable constraints on the lahar source parameterization. However, when testing the calibrated model for other larger events (e.g. Typhoon Rolly) the hydrological model alone is insufficient to describe lahar initiation, with field evidence indicating substantial mobilization of material by landsliding.

We extended the formulation of the LaharFlow model to allow assignment of spatially-varying erodibility as would be important as lahars flow over different rural terrain and eventually to urban environments. A key outcome from this research is that the influence of spatially-varying erosion for flow over different land-cover types is very significant for the model predictions, comparable to the influence of topography. For highly erosive flows, the ability of the flow to alter channel morphology during a single event can lead to flow routing that differs substantially from pre-event channels. Observations at Mayon volcano showed this occurred during recent typhoons. Erosion is limited by land cover characteristics, which we have incorporated into the model through a land-cover map derived from satellite observations and field work. Parameters to characterise the erodibility of different land cover types have been informed by literature on soil erodibility, adjusted through calibration studies to apply to highly energetic lahar flows. Additionally, we have developed methods to amend existing topographic maps to account for channel morphological changes, adopting 'stream-burning' methods informed by field work.

The calibration of the coupled Decipher-LaharFlow model raised two important issues that modified the research plans in the project. Firstly, analysis of the calibration model runs highlighted instabilities in the model solutions. We conducted mathematical analysis of these instabilities, showing that many operational shallow layer models that incorporate morphodynamics such as LaharFlow are inherently mathematically 'ill-posed' meaning that instabilities can grow without bound, creating unreliable model
predictions. We analysed this behaviour in detail and proposed two strategies that provably alleviate this problem. Our analysis was conducted in a framework that incorporates a very general class of systems and consequently can be used to inform future model development for lahar flows and many other related settings. This work was published in one journal paper and a follow-up paper that applies this generalised approach to study instabilities in travelling waves is currently under review.

Two components of the originally proposed research have not been completed: (1) the lack of gauging data for hydrological modelling meant that this approach was unsuitable for exploring the potential impacts of future climate change. Instead, we have conducted a scenario-based investigation of potential future lahars in the Pasig-Potrero river system at Pinatubo volcano where flood defences were built following the 1990 eruption of Pinatubo. This is an area of particular interest in the Philippines, with current development plans in this region. We assessed the exposure of communities to flows of comparable scale to the lahars following the 1990 eruption, which are considered plausible if there is renewed volcanic activity and typhoons. Our simulations suggest that the flood defences offer protection, but that encroachment of development within the defence structures leaves some communities vulnerable. Additionally, we highlighted the potential vulnerability of the defence structures to channel morphological change, which is considered likely during future storms given the poorly consolidated volcanic deposits. These results were shared with local authorities and communities at a project stakeholder workshop; (2) the additional analysis required to characterise and alleviate ill-posedness in the models meant that we could not develop new mathematical analyses of lahar impacts on structures. Instead we have developed sufficient understanding of lahar damage through analysis of field observations to quantify risk metrics, and are implementing a workflow for quantifying lahar risk in the Philippines REDAS national risk assessment tool.

The new modelling capability will be used by PHIVOLCS to conduct lahar hazard assessments for other Philippine volcanoes, and one of their temporary staff supported and trained in lahar modelling by the project has taken up a permanent position in PHIVOLCS to take this work forward. The new approaches for assessing lahar risk are being implemented in the REDAS system to be applied more widely across the Philippines. Our model developments and insights from our studies of lahar initiation and quantification of lahar risk will inform future quantification of lahar hazard and risk.
Exploitation Route The new modelling capability will be used by PHIVOLCS to conduct lahar hazard assessments for other Philippine volcanoes, and one of their temporary staff supported and trained in lahar modelling by the project has taken up a permanent position in PHIVOLCS to take this work forward. The new approaches for assessing lahar risk are being implemented in the REDAS system to be applied more widely across the Philippines. Our model developments and insights from our studies of lahar initiation and quantification of lahar risk will inform future quantification of lahar hazard and risk.
Sectors Communities and Social Services/Policy,Digital/Communication/Information Technologies (including Software),Environment

Description Our activities have engaged local government and planning units around Mayon and Pinatubo volcanoes in processes of assessing lahar hazard and risk, and our research is informing decision-making around current and future lahar hazard. We held a workshop to train local government units in assessing lahar hazard and risk in November 2021 and also presented the results of modelling of lahar defences around Pinatubo and highlighted potential risk to communities expanding close to these structures. We have provided extensive training in lahar hazard modelling (>80 hours) to the Philippine Institute of Volcanology and Seismology (PHIVOLCS, our project partners), which has resulted in a new permanent post in PHIVOLCS in modelling and new capability to conduct lahar hazard assessment for other Philippine volcanoes. Our new modelling tools are being incorporated in the Philippine national risk assessment tool REDAS, to enhance capability for national and local government to make risk-informed decisions around lahar preparedness.
First Year Of Impact 2021
Sector Communities and Social Services/Policy,Digital/Communication/Information Technologies (including Software),Environment
Impact Types Societal

Description Philippines Institute of Volcanology and Seismology 
Organisation Philippine Institute of Volcanology and Seismology
Country Philippines 
Sector Public 
PI Contribution PHIVOLCS are country partners for the project, which is jointly funded by the Newton Fund (UK) and PCIEERD (Philippines). My research team is conducting research on modelling volcanic lahars in the Philippines, and working with PHIVOLCS to test and apply the models to Pinatubo and Mayon volcanoes.
Collaborator Contribution PHIVOLCS are country partners for the project, which is jointly funded by the Newton Fund (UK) and PCIEERD (Philippines). PHIVOLCS are conducting field research to provide data for model testing, and will be using our modelling tools to develop hazard and risk assessments for Pinatubo and Mayon volcanoes.
Impact This is a multidisciplinary collaboration between geologists, hydrologists, mathematicians and experts in risk. There are no outputs yet.
Start Year 2019
Description Engagement event with Local Government Units in in Pampanga, Zambales and Albay Provinces, Philippines 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Policymakers/politicians
Results and Impact 20 Mayors, local government and planning officials met with the project team to co-develop plans and locations for field study sites and to formalise involvement with the project. The Local Government Units agreed to participate in the project, and they have started to gain knowledge about lahar hazards and their mitigation
Year(s) Of Engagement Activity 2020
Description Workshop - Strengthening community preparedness through prediction of lahar inundation and loss estimation for the pilot communities at Pinatubo and Mayon Volcanoes 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Policymakers/politicians
Results and Impact The workshop involved knowledge exchange about lahar hazard and risk assessment with local government representatives from communities around Mayon and Pinatubo volcanoes and with national government institutions. The workshop resulted in co-developed practices for local lahar risk assessment.
Participants were from the following organisations:
? Provincial and Municipal DRRM Offices, Planning and Development Offices, Engineer's and Assessor's offices, Environment and Natural Resources Offices
? Local officials from the project's pilot barangays (Manibaug Libutad, Porac, Pampanga; San Francisco and Iraya, Guinobatan, Albay)
? State Universities (Bicol University and Don Honorio Ventura State University)
? Observers from DOST-Philippine Council for Industry, Energy, and Emerging Technology Research and Development (PCIEERD), PHIVOLCS-Volcano Monitoring and
Eruption Prediction Division (VMEPD) Volcano Observatories and National Environmental Research Council (NERC)
Year(s) Of Engagement Activity 2021