Weather-Related Natural Disasters: Should We Be Concerned About a Reversion to the Mean?

By Roger Pielke Jr – Re-Blogged From Risk Frontiers

The world is presently in an era of unusually low weather disasters. This holds for the weather phenomena that have historically caused the most damage: tropical cyclones, floods, tornadoes and drought. Given how weather events have become politicized in debates over climate change, some find this hard to believe. Fortunately, government and IPCC (Intergovernmental Panel on Climate Change) analyses allow such claims to be adjudicated based on science, and not politics.  Here I briefly summarize recent relevant data.

Every six months Munich Re publishes a tally of the costs of disasters around the world for the past half year. This is an excellent resource for tracking disaster costs over time.  The data allows us to compare disaster costs to global GDP, to get a sense of the magnitude of these costs in the context of economic activity.  Using data from the UN, here is how that data looks since 1990, when we have determined that data is most reliable and complete.

The data shows that since 2005 the world has had a remarkable streak of good luck when it comes to big weather disasters, specifically:

  • From 2006 to present there have been 7/11 years with weather disasters costing less than 0.20% of global GDP.
  • The previous 11 years saw 6 with more than 0.20% of global GDP.
  • From 2006 to present there has be zero years with losses greater than 0.30% of global GDP.
  • The previous 11 years had 2, as did the 6 years before that, or about once every 4 years.
  • According to a simple linear trend over this time period, global disasters are 50% what they were 27 years ago, as a proportion of GDP.

Why has this occurred? Is it good luck, climate change or something else?

By disaggregating the data phenomenon by phenomenon we can get a better sense of why it is that disaster costs are, as a proportion of global GDP, so low in recent years.

A good place to start is with tropical cyclones, given that they are often the most costly weather events to occur each year.  The figure below shows global tropical cyclone landfalls from 1990 through 2016. These are the storms that cause the overwhelming majority of property damage. Since 1990 there has been a reduction of about 3 landfalling storms per year (from ~17 to ~14), which certainly helps to explain why disaster losses are somewhat depressed.

Even more striking is the extended period in the United States, which has the most exposure to tropical cyclone damage, without the landfall of an intense hurricane. The figure below shows the number of days between each landfall of a Category 3+ hurricane in the US, starting in 1900. As of this writing the tally is approaching 4500 days, which is a streak of good fortune not seen in the historical record.

A very conservative estimate of the effects of this “intense hurricane drought” is that the United States is some $70 billion in arrears with respect to expected hurricane damage since 2006. In fact, it is not widely appreciated but the US has seen a decrease of about 20% in both hurricane frequency and intensity at landfall since 1900. I urge caution placing too much significance on linear trends, as they are quite sensitive to start and end dates, but there is very little to indicate that tropical cyclones are either more frequent or intense.

Data on floods, drought and tornadoes are similar in that they show little to no indication of becoming more severe or frequent.  The IPCC concludes:

  • “There continues to be a lack of evidence and thus low confidence regarding the sign of trend in the magnitude and/or frequency of floods on a global scale.”
  • “There is low confidence in observed trends in small spatial-scale phenomena such as tornadoes and hail.”
  • “There is low confidence in detection and attribution of changes in drought over global land areas since the mid-20th century.”

Thus, it is fair to conclude that the costs of disasters worldwide is depressed because, as the global economy has grown, disaster costs have not grown at the same rate. Thus, disaster costs as a proportion of GDP have decreased. One important reason for this is a lack of increase in the weather events that cause disasters, most notably, tropical cyclones worldwide and especially hurricanes in the United States.

Climate change, of course, is all too real and has a significant human component. The IPCC has concluded that there is evidence indicating that heat waves have become more common as too has extreme rainfall in some parts of the world.  Projections for the future suggest that some other types of extremes – including tropical cyclones, floods, drought and tornadoes – may yet become more intense or frequent. However, there is great uncertainty about how extremes will evolve in the climate future.

But we don’t need climate scenarios to be worried about more disasters. To the extent that people believe that we are presently in an era of large or unusual disasters, many will be in for a shock when large weather disasters again occur. And they will. A simple regression to the mean would imply disasters of a scale not seen worldwide in more than a decade.

Consider that 2005 saw weather disasters totaling 0.5% of global GDP. In 2017, if the world economy totaled $90 trillion (in a round number), then an equivalent amount of 2017 disaster losses to the proportional costs to 2005 GDP would be about $450 billion. That is about equivalent to Hurricane Katrina, Superstorm Sandy, Hurricane Andrew, the 2011 Thailand floods, the 1998 Yangtze floods all occurring in one year plus about $100 billion more in other disaster losses. And there is no reason why we should consider 0.5% of GDP to be an upper limit. Think about that.

The world has had a run of good luck when it comes to weather disasters. That will inevitably come to an end. Understanding loss potential in the context of inexorable global development and long term climate patterns is hard enough.  It is made even more difficult with the politicized overlay that often accompanies the climate issue. Fortunately, there is good science and solid data available to help cut through the noise. Bigger disasters are coming – will you be ready?

CONTINUE READING –>

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