Accounting for tropical cyclones more than doubles the global population exposed to low-probability coastal flooding

This report discusses how storm surges that occur along low-lying, densely populated coastlines can leave devastating societal, economical, and ecological impacts. To protect coastal communities from flooding, return periods of storm tides, defined as the combination of the surge and tide, must be accurately evaluated. Here it presents storm tide return periods using a novel integration of two modelling techniques.

For surges induced by extratropical cyclones, we use a 38-yeartime series based on the ERA5 climate reanalysis. For surges induced by tropical cyclones, the report uses synthetic tropical cyclones from the STORM dataset representing 10,000 years undercurrent climate conditions. Tropical and extratropical cyclone surge levels are probabilistically combined with tidal levels, and return periods are computed empirically.

The report estimates that 78million people are exposed to a 1 in 1000-yearflood caused by extratropical cyclones, which more than doubles to 192 M people when taking tropical cyclones into account. The results how that previous studies have underestimated the global exposure to low-probability coastal flooding by 31%.