Conducting a quantitative risk assessment is often a difficult process, requiring data that is sparse or even unobtainable. With volcanoes, the effects of uncertainty are accentuated by the potentially high costs of making a wrong call.

Guatemala has many active volcanoes, but none are as close to large populations as the ‘Volcán de Fuego’, potentially one of the most dangerous volcanoes in Central America with a large population surrounding it. Many farmers live and work in its shadow due to the fertile slopes that provide the best ground for coffee growing in the region. Large eruptions in 1974 fortuitously did not lead to any deaths, but buried in the volcano’s geological history are signs of ominous behaviour.

Using Monte Carlo sampling to quantify the threat
The volcano has been very active over the last few years with many small eruptions taking place every day, and the fear that this activity could suggest the build up towards larger eruptions in the future is a worrying prospect. The “Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hidrologia” (INSIVUMEH), regularly monitors activity at the volcano, however, despite the gallant efforts of the scientists there, no formalised risk assessments are carried out, mostly due to lack of funding and resources.

Recent work using Palisade’s The DecisionTools Suite however, is now enabling volcanologists to quantify the nature of one of the threats from the volcano to peoples’ lives. As an integrated set of programmes for risk analysis and decision making under uncertainty, The DecisionTools Suite running in Microsoft Excel, allows access to Monte Carlo simulation and other advanced analytics quickly and simply on the desktop.

A different approach to risk assessment
Conventional risk assessments attempt to model the probability of a hazard and combine that with the vulnerability of the population, to create societal risk curves and estimated values of Individual Risk per Annum (IRPA). For many of the people living on the slopes and indeed the authorities, knowing the potential number of deaths or cost from an eruption is not entirely useful, as little planning control or mitigation can be carried out.  In an attempt to increase the usefulness of the risk modeling to the end-user (the authorities and people living near the volcano), BRISK has looked at the vulnerability in a different way.

Normally volcanic risk assessments assume that the whole population is present in a location when a hazard hits. However, new work by BRISK has modeled the likelihood of a successful evacuation, using both @RISK and PrecisionTree, by inputting several variables obtained through a process of structured expert judgment. These variables, which include the time taken between a possible eruption and a possible hazard hitting a location, along with communication times from authorities and evacuation times, are each estimated with an uncertainty distribution by the experts. These expert views are then weighted and pooled together. The variables are then constructed together in a logic tree within Palisade’s PrecisionTree, with the end node either being evacuation or no evacuation – and the probability of these outcomes being quantified, with their uncertainties. When fed back into the @RISK (Hazard * Vulnerability) model, the effects of a potential evacuation on the risk is very clear.

Better planning and effective mitigation strategies
When looking in more detail at the model outputs from the logic tree, it became clear where the sensitivities were within the system. For example, it may be for a given location that the amount of time between a warning and the hazard hitting is crucial, or it may be that the time taken to evacuate is crucial. This new way of modeling volcanic risk informs better planning and more effective mitigation strategies.

Jonathan Stone, a researcher at the University of Bristol, working with colleagues Prof Willy Aspinall¹ and Dr Matt Watson, said “Palisade’s DecisionTools Suite has proved to be invaluable in the work we are doing with INSIVUMEH, and potentially very useful for those living and working around Volcán de Fuego.”

¹Professor Willy Aspinall has been using Palisade’s @RISK software for some time in his work analysing the risk of volcanic eruptions and earthquakes around the globe.  His work was documented in the following article.

» @RISK
» Bristol Environmental Risk Research Centre (BRISK)