Extreme hazards — rare, high-impact events — pose a serious and underestimated threat to humanity. The extremes of the broad ensemble of natural and anthropogenic hazards can lead to global disasters and catastrophes. Because they are rare and modern society lacks experience with them, they tend to be ignored in disaster risk management. While the probabilities of most natural hazards do not change much over time, the sensitivity of the built environment and the vulnerability of the embedded socio-economic fabric have increased rapidly. Exposure to geohazards has increased dramatically in recent decades and continues to do so. In particular, growing urban environments — including megacities — are in harm’s way. Because of the increasing complexity of modern society even moderate hazards can cause regional and global disasters. Natural hazards that occur frequently on our dynamic planet are increasingly causing loss of human life and damage to goods and infrastructures at the local, regional and global scale, depending on their intensity.
The Science Position Paper
The Science Position Paper Extreme Geohazards: Reducing the Disaster Risk and Increasing Resilience analyses the potential effects of low-probability high-impact events, which might cause global disasters and even bring our already stressed global society beyond the limits of sustainability.
The paper, a joint initiative by the European Science Foundation (ESF), the Group on Earth Observations (GEO) and the Geohazard Community of Practice (GHCP), following a high-level ESF-COST Conference on the subject, addresses several types of geohazards, but puts special emphasis on the impending risk of catastrophic effects on populations and infrastructures should our growing and increasingly interconnected modern society be exposed to a very large volcanic eruption. The paper highlights the urgency of establishing an effective dialogue with a large community of stakeholders in order to develop robust risk management, disaster risk reduction, resilience, and sustainability plans in the coming years and decades. It also underlines the need to develop the methodology to assess the potentially global impacts that a major hazard would have on our modern society, which would provide guidance to reduce vulnerability where possible and increase general resilience in the face of surprise events. It concludes that preparedness requires a global monitoring system that could provide sufficiently early warnings, should such a major hazardous event develop.
The report is to be presented at a special session during the European Geosciences Union General Assembly (EGU) in Vienna on Tuesday 14 April 2015, 13:30 - 15:00. The EGU General Assembly is an event that brings together geoscientists from all over the world which makes it the perfect place to deliver such a publication. For more information on the event, see the event page ...
Background and Motivation
The Declaration on Extreme Geohazards and Disaster Risk Reduction accepted by the participants of the European Science Foundation conference on “Understanding Extreme Geohazards: The Science of the Disaster Risk Management Cycle” held on November 28 to December 1, 2011 in Sant Feliu de Guixols, Spain emphasizes the need for a community-based “white paper” addressing the scientific and societal challenges of increasing disaster risk due to extreme geohazards. This paper was to be distributed to funding agencies and governmental and intergovernmental bodies. The main reasoning for this recommendation was in the observation that despite many international efforts and significant improvements in our knowledge of the hazards, the disasters caused by extreme geohazards are increasing. A key reason for these conflicting trends are in a biased risk perception particularly with respect to the rare, high-impact events at the upper end of the hazard intensity spectrum. The goal of the recommended paper was to provide a basis for a more realistic risk perception.
The main goal of the paper was to assess the disaster risk associated with extreme geohazards and to inform mitigation of this risk. In a risk-based approach, the risk can be quantified as hazard probability time vulnerability of the exposed assets time the value of the assets. More detailed, for a given hazard h, a given recurrence time interval T, and for a prescribed intensity I, the associated risk r(I) expressed in currency is given by
where x is the location, t time, p the probability density function(PDF) of the hazard giving the probability that the hazard with intensity I will occur in the considered recurrence interval, V the vulnerability of an asset a for hazard h at intensity I, and a being the asset exposed at location x (Plag and Jules-Plag, 2013). To assess the total risk R associated with a hazard, we can use
These two equations provide a basis for risk management and the prioritizing of mitigation, adaptation and monitoring. The risk is strongly dependent on the chosen recurrence time interval. Selecting a short time interval may seriously underestimate the risk, while a very long interval may lead to unrealistically high risks.
Any effort to mitigate the disaster risk impacts the risk and reduces the expected costs of a disaster. The goal is to find the point where the total cost of mitigation and disaster risk are a minimum. This is expressed by the diagram in Figure 1. However, the determination of the point n* is complicated by uncertainties in the risk, i.e., the hazard propability and the vulnerability of the assets, and these uncertainties increase dramatically towards the rare, high-impact events. Understanding the uncertainties is crucial for an informed decision on where to put n*.
Figure 1: The optimal point for mitigation is n*, that is, the point where the total costs of mitigation and expected disaster costs is minimum. The red lines indicate the uncertainties in total costs due to uncertainies in the risk. Modified from Stein and Stein (2012).
The above approach has considerable problems at the extreme end of the hazard spectrum, where statistics are insufficient and experience with hazard occurrence is often lacking. The paper was to focus on this part of the hazard spectrum and consider alternative “best practices” to address the problems of low-probability, high-impact events. For these events, the “minimum-costs” approach summarized in Figure 1 may not be a good choice and an approach focusing on what is necessary to ensure a minium survival of our civilization should such an event occur may be more appropriate.