This paper provides a timely review of progress and ongoing research needs in tsunami hazard and risk science since the most recent major event, the Tohoku tsunami in 2011. The tsunami community has made significant progress in understanding tsunami hazard from seismic sources. However, this is only part of the inputs needed to effectively manage tsunami risk, which should be understood more holistically, including non-seismic sources, vulnerability in different dimensions and the overall societal effects, in addition to its interaction with other hazards and cascading effects. Moreover, higher standards need to be achieved as far as the management of subjective choices and uncertainty quantification, which largely govern the basis for tsunami risk decision making.
Large tsunamis occur with relatively low frequency, if compared for instance with the ones of other perils such as hurricanes, floods and landslides, but have potentially high impacts including extreme numbers of casualties, and direct and indirect economic losses. In the last two decades this has been demonstrated, for instance, by the Indian Ocean (2004) and the Tohoku (2011) tsunamis. The scale of these disasters far exceeded the previously perceived risk in these areas. The relative rarity of tsunamis implies in fact a deficit of tsunami observations, which forces hazard and risk analysts to make subjective modelling choices. This in turn makes the uncertainties associated with tsunami risk analysis quite large. One likely reason for the underestimation of tsunami risk is the lack of rigorous, robust and standardized hazard and risk assessment methodologies, and the treatment of such large uncertainties.
Since 2004, methodologies such as probabilistic tsunami hazard analysis (PTHA) have emerged, which are increasingly used to address the above-mentioned issues. PTHA has focused thus far on tsunamis triggered by earthquakes. Further work is required to characterize events triggered by landslides, volcanoes, and meteorological loading, particularly in the frame of the current move towards the consideration of multiple hazards in disaster risk management, as shown by the multi-hazard context of the Global Risk Assessment Framework (GRAF). Additionally, the understanding of tsunami risk is not yet at the same level as the understanding of the hazard. To bring tsunamis up to speed in the context of the first priority of the Sendai Framework for Disaster Risk Reduction: “Understanding disaster risk”, practitioners must work to develop a sound Probabilistic Tsunami Risk assessment (PTRA) methodological framework. PTRA is intended to become a key component of effective tsunami risk management, applicable from urban to regional scales.
This background paper mostly reviews recent progress in tsunami hazard analysis and risk analysis. It also briefly sets out the future work required to improve tsunami risk understanding, management and coastal resilience. In particular, the paper will seek to highlight current major gaps in tsunami risk understanding that need to be addressed, such as tsunami vulnerability (in several of its dimensions), the societal effects of tsunami risk, and tsunami in multi-hazard contexts and as a contributor to cascading risk.
This paper is a contribution to the 2019 edition of the Global Assessment Report on Disaster Risk Reduction (GAR 2019).
To cite this paper:
Løvholt, F. et al. Global trends in advancing tsunami science for improved hazard and risk understanding. Contributing Paper to GAR 2019