Mortality due to storm surges is on the way down, and has been for a long time as a result of better forecasting, evacuation and coastal protection, according to new research. But this may not always be the case as sea levels rise in a warming world.
Storm surges—the abnormal rise in seawater level above the normal tide caused by a storm—have the highest death tolls per event of any natural disaster apart from earthquakes. They are one of the main causes of fatalities from hurricanes. For example, both hurricanes Frederic and Katrina were category 3 events, but only Katrina caused surge flooding. The former resulted in five deaths; the latter hundreds. And storm surges are predicted to worsen under climate change as sea levels rise.
A key challenge is that long-term projections of sea-level rise and storm activity from climate change remain uncertain, as do societal changes such as population growth and the magnitude and distribution of socio-economic impacts, resulting in a large number of impact scenarios. How are coastal cities, like those in BC, able to engage in storm-surge adaptation measures when they do not know which is correct?
The researchers, who released their findings this year in the Environmental Research Letters journal, analyzed a list of storm surge events around the world dating back to 1900. There is some good news. Total annual fatalities globally from major storm surges have declined since the 1960s. Between 1900-2015, on average, there were 8,342 fatalities and 1.5 million people affected per year. There are still surge events with staggering death counts such as Cyclone Nargis that hit Myanmar in 2008, killing more than 100,000, and some 71 percent of the deaths over this same period occurred in South Asia.
The researchers stress how impressive this is, as over this same period, the world’s population has increased six-fold, with a great deal of this occurring in coastal zones. Mortality—the ratio of the people killed to the number exposed to the event—has also declined in almost all regions. Decline in fatalities and mortality is due to improvements in flood protection, forecasting, the quality of residential buildings, early warning systems and evacuation. They blame high mortality in Myanmar on insufficient protection, forecast and early warning systems.
But we should not rest on our laurels, the researchers say. It remains to be seen whether global adaptation measures that have proven successful so far will continue to be so as sea level rise produces greater flood depths. Subsidence and continued coastal population growth may also impact future numbers moving forward.
To help fill knowledge gaps, PICS-supported researcher Jackie Yip at the University of British Columbia is deploying machine learning to identify coastal flooding impact patterns across a range of possible future scenarios, or “archetypal patterns” of impacts. Strategies based on these impact patterns are likely suitable even if the actual climate impacts diverge from what has been predicted. This method, still under development, investigates impact patterns for the City of Vancouver up to 2100, but aims to be applicable to cities worldwide.
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