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11 Aug 16 14:39

If you have but a basic notion of global tropical cyclone risk and geography, then you know the answer: No, the Rio de Janeiro Olympic Games in Brazil are not at risk. Firstly, it's winter time in the southern hemisphere. Secondly, the South Atlantic never experiences tropical cyclones... or does it, after all?

For a long time, the South Atlantic was assumed to be an ocean basin in which tropical cyclones do not occur. This thinking had to be changed fundamentally when a tropical cyclone named "Catarina" struck Brazil in March 2004. In addition to a number of casualties, people living in the affected areas along the southern coast of the country suffered considerable damage to property, infrastructure and agriculture. Prior to this event, such destruction from a tropical cyclone had been deemed impossible in Brazil.

So why are tropical cyclones in the South Atlantic so rare? Two years ago, Swiss Re teamed up with the department of Atmospheric and Climate Science at ETH Zürich to address exactly this question. The scientific consensus thus far was based on a 1968 paper by the late hurricane researcher Prof. William Gray, which attributed the absence to strong vertical wind shear. The ETH Zürich study confirmed this being a key factor inhibiting cyclone formation, in particular in the western South Atlantic, off the coast of Brazil. Adding to the difficulties in generating tropical cyclones is the relative absence of precursory lows (in other ocean basins fueled by the intertropical convergence zone or tropical waves) as well as the comparatively low sea surface temperatures. The study identified these latter two as the dominant factors inhibiting cyclone formation in central and eastern portions of the South Atlantic.

We summarised these findings in a Swiss Re publication entitled "The risk of tropical cyclones in Brazil" ( available in both English and Portuguese ). We went on to estimate the impact tropical cyclones similar to the 2004 Catarina storm would have on the Brazilian insurance sector, if it were to strike a more populated portion of the coast. Last but not least, the report contains a hazard map identifying areas we consider to be at risk – and Rio de Janeiro is generally located within this hazard zone. However, as mentioned before: no risk currently, during the southern hemisphere wintertime.

Have there ever been summer Olympics that could have been severely impacted by a tropical cyclone? The 1964 Games, held from October 10th-24th in Tokyo, Japan, probably deserve the honor of the most risky Olympics so far in this respect. They did take place a little after the peak of the Pacific typhoon season (second half of September). But obviously, that's no guarantee… Hurricane Sandy struck the US North East coast in 2012 at the end of October, also well past the North Atlantic hurricane season peak. By the way: Tokyo will be hosting the Games once more in 2020, but this time from the end of July until early August.

Being a considerable sports fan I hope the Olympic Games will never come to a halt due to a tropical cyclone or any other natural disaster. However, if they ever would, the insurance industry would assume a significant part of the financial burden arising. Such gigantic events present an immense accumulation of risks peaking within a short two-week period. So property damage, third-party liability, event cancellation and many more risks are transferred to domestic insurers, which in turn cede large portions out into the international reinsurance market. As such, not only the Olympic Games themselves are a truly international affair, the distribution of financial risk associated with these events equally is.


Category: Climate/natural disasters: Disaster risk, Floods/storms

Location: Rio de Janeiro, Brazil


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