Tonga

Risk profile: Sudden-Onset Hazards and the Risk of Future Displacement in Tonga

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Summary

Disaster displacement is one of the world’s biggest humanitarian and sustainable development challenges, and climate change and urbanisation serve to aggravate the phenomenon.

IDMC has built upon the risk analysis developed by the United Nations Office for Disaster Risk Reduction to look at future displacement risk associated with sudden-onset hazards such as earthquakes, tsunamis, cyclonic winds and storm surges. The analysis considered a wide range of hazard scenarios, their likelihood and their potential to cause housing damage, which serves as a proxy for displacement. At this stage, our model’s current resolution, however, did not enable us to assess the risk associated with riverine floods in small island states.

This technical paper presents the initial results of our efforts to assess the risk of displacement associated with disasters and climate change in Tonga. In addition of risk information, the paper looks more broadly at the social and demographic context, events from the past that triggered internal displacement and government initiatives linked to displacement and more generally to disaster risk reduction.

It examines risk levels and uncertainties for sudden-onset hazards by type to produce a baseline country risk profile via two national-level metrics:

• Probable Maximum Displacement (PMD) is the maximum displacement expected within a given time period, and determines outlier events that could occur during it.

• Average Annual Displacement (AAD) is a compact metric that represents the annualised accumulated effect of small to medium and extreme events and predicts the likely displacement associated with them on a yearly basis.

Cyclone winds represent Tonga’s highest displacement risk. There is a 64 per cent probability that in the next 50 years about 21,400 people will be displaced as a result of cyclonic winds in the archipelago. This is the country’s PMD.

About 1,229 people on average are likely to be displaced during any given year in the country by sudden-onset hazards, such as earthquakes, tsunamis and cyclonic winds. This is the ADD metric.

Displacement risk is determined by three factors:

  1. Hazard: the likelihood of different hazards and their intensity

  2. Exposure: the number of people and assets exposed to hazards

  3. Vulnerability: the likelihood of exposed houses and buildings being damaged or destroyed