Stormwatch–they’re getting stronger

For the US and the islands of the Caribbean, 2017 was one of the most disastrous years on record—with three major hurricanes ripping through the region. But it turns out that, globally, things were pretty much average.

Compared to the previous decade (2007-2016), there were fewer natural disasters, fatalities, and total people affected in 2017–but, and this is the key stat, the disasters that occurred caused much more damage.[1]

The EM-DAT database keeps track of nine types of natural disasters : drought, earthquakes, extreme temperature, floods, landslides, mass movement (the dry kind), storms, volcanoes, and wildfires.  And for each of these categories, it counts the number of occurrences (usually several hundred), the number of fatalities (generally in the thousands), the number of people affected (which is counted in millions), and the economic impact—measured in billions of dollars. The final numbers for 2017 have just been published.

There were 335 natural disasters in 2017—a little less than the annual average of 354. The number of people killed in these disasters was down compared to the previous decade (because of several catastrophic high-mortality events during that time), and the number of people affected was also significantly less than the decadal average.   But one metric was considerably higher. The table below shows the big numbers.

After 2011, when a devastating earthquake and tsunami caused massive damage in Japan, last year was the most costly in a decade due to the powerful hurricanes that tore across the US and the Caribbean.  These included Harvey, Irma, and Maria costing $95 billion, $80.7 billion, and $69.7 billion respectively.

Looking more closely at the type of disasters that occurred last year, there were more storms (+29.6%), more wildfires (+60%), and more landslides (+47.1%) compared to the previous decade.

The table below shows data for the types of events scientists believe are most likely to be accelerated by the changing climate.

Storms and wildfires were above average in 2017; other types of natural disasters occurred less frequently. [2] But what stands out is the huge economic impact of the hurricanes and cyclones that ravaged the US, the Caribbean, and Asia last year: costing almost 285 billion dollars

It’s interesting that although there were several more storms that the decadal average, the number of fatalities was a lot less than the average–but the economic impact was a great deal more.  This apparent paradox might suggest that although storms are becoming more destructive and causing greater damage, people at risk are getting better at avoiding them–perhaps due to improved communications and better information that enables them to get to safety sooner.  The greater destruction that storms are causing could be due to storms occurring more frequently in areas with a higher level of built and valuable infrastructure (which seems an unlikely explanation), or by storms simply gaining in strength—as indicated by their wind speeds, or because they are impacting a larger area, or perhaps because they are causing much more flooding.[3]

The most likely explanation of the increased economic impact caused by storms is some combination of the factors that contribute to their destructive impact: windspeed, size, and their potential to cause flooding.

The latter metric is related to how much rain the storm can dump on an area–which in turn is a function of the speed at which the storm is moving (or not)–as we saw last year with Harvey and this year with Florence, and the amount of water precipitated by the storm.  In fact, there is evidence that storms are moving more slowly—giving them more time for heavy rain to fall and increasing the likelihood of catastrophic flooding.[4]

In this regard, the Saffir-Simpson scale (which measures only windspeed) is not only inadequate, it’s dangerous.  When Florence was ‘downgraded’ from a category 4 storm to category 1 as it neared the US east coast, many people in vulnerable locations decided not to evacuate.  This was a mistake that may have cost several people their lives.

A new way to classify storms is badly needed.  Introducing a category 6 for a storm with very high windspeeds certainly conveys the message that this is a very dangerous storm.  But then most people would assume that a category 1 storm is a lot less dangerous—and this may absolutely not be the case because of the storm’s potential to cause catastrophic flooding.  So storms need to be classified according to the level of hazard they present. Something like a HazCat: on a scale from 1 to 10.

One takeaway when looking at the EM-DAT data, is that storms are becoming more destructive—not so much in terms of fatalities, but in terms of the infrastructure that they are capable of destroying. The two graphs below show the frequency of storms (left panel) and their economic impact (right panel) over the last 50 years.

Although the long-term trend of storm frequency is clearly upwards, since about 2000 there has been no clear trend—although there is now much greater variability.  So there is less evidence to support the assertion that storms are becoming more frequent.

But as right hand panel shows, there are clear signs that hurricanes and cyclones are slowing gaining in destructive power. We might dismiss the spikes in 2005 and 2017 as anomalies. But with the economic impact of Florence not yet fully evaluated but certain to be tens of billions of dollars, and looking at the enormous destruction caused by super-cyclone Mangkhut that tore through the Philippines, Hong Kong and China at about the same time that Florence was inundating the Carolinas, 2018 is shaping up to be another record year.

And the season’s not yet over.  Last year, hurricanes Nate and Orphelia showed up the first weeek of October.





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[1] The numbers reported here and shown in the graphs are from the International Disaster Database (called EM-DAT) managed by the Centre for Research on the Epidemiology of Disasters (CRED) at the Université Catholique de Louvain The database can be accessed here : . The data for 2017 were first reported in CRED Crunch No. 50 earlier this year but have now been updated and presented in more detail. The CRED Crunch bulletin can be found at  :

[2] For a disaster to be recorded in the EM-DAT database it must satisfy one of the following criteria : 10 or more people killed; 100 or more people affected; a declaration of a state of emergency; or a call for international assistance. This might explain why only 15 of the dozens of fires that blazed through California, British Columbia and Ontario in Canada in 2017 were recorded.

[3] Since flooding events caused by hurricanes and cyclones, including their fatalities and damage, are attributed to the ‘storm’ category, they do not show up separately in the data shown above—which is perhaps why the occurrence of floods has not increased the way that the frequency of storms has.

[4] See: Recent scientific advancements show new connections between climate change and hurricanes, at : ; and also the recent paper in Nature magazine: A global slowdown of tropical-cyclone translation speed, at : . And check out this article: Florence was another 1,000-year rain event. Is this the new normal as the planet warms?  At:



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