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A “Truthier” Look at Tornadoes?

In late June of 2013 I ran a 3-post series on the frequency of tornadoes in the United States and in Missouri (starts here). Statistics show a marked increase in the total number of tornadoes, but I concluded that the increase derived from improved detection, which was catching many small ones that had previously escaped notice.

Source: Tornado Climatology page of the National Climate Data Center

Source: Tornado Climatology page of the National Climate Data Center

Regarding the most powerful tornadoes (EF 3-5), I said “…it seems pretty clear that there is no overall trend toward increasing frequency. In fact, if anything, the trend has been towards decreased frequency – there are fewer highly destructive tornadoes now than there were during the mid-1960s.”

Click on chart for larger view.

Now a post in Andy Revkin’s Dot Earth blog takes up the issue. Richard Muller, the physicist and climate change denier who gained national attention by conducting an independent analysis confirming that humans were warming the planet, wrote an op-ed piece saying what I said: there are fewer of the most destructive tornadoes. Paul Markowski and five others wrote a reply claiming that the apparent decline comes from a tightening of reporting standards over time. Tornado frequencies prior to the 1970s were created retrospectively by meteorology graduate students, and suffered from “grade inflation.” In 2003, new policies required additional (and expensive) analysis of every severe tornado. According to Markowski et al, this led to the systematic and intentional under-counting of severe tornadoes after 2003 in order to avoid increased costs. Markowski and his colleagues are meteorologists at several different institutions.

Errors plague all attempts to develop historical climate data. The basic thrust of the scientific process is that a hypothesis is produced, then somebody criticizes it. If the criticism is valid, a new and better hypothesis wins adoption. Then a new criticism arises, followed by more improvement.

It seems to me, however, that systematic and intentional under-counting is a fairly serious accusation, roughly equivalent to falsifying data. Although Markowski et al seem positioned to be “in the know,” they make the accusation without citing any supporting evidence. If the NOAA data is intentionally under-reporting tornado severity, it needs to be proved and corrected.

For now, I stick with my original statement: for whatever reason, the data show no overall trend toward increasing frequency of severe tornadoes. If anything, the trend shown in the data is towards decreased frequency. The data may need to be corrected, but for now, this is what they show.

Sources:

The MoGreenStats Blog. “Tornadoes In and Around Missouri,” blog entry by John May, 6/24/2013.

The MoGreenStats Blog. “Tornadoes Seem More Frequent, But They Aren’t,” blog entry by John May, 6/29/2013.

The MoGreenStats Blog. “The Most Powerful Tornadoes Are Less Frequent,” blog entry by John May, 7/1/2013.

Revkin, Andrew. 2013. “A Closer Look at Tornadoes in a Human-Heated Climate.” Dot Earth (blog), New York Times, 12/9/2013, http://dotearth.glogs.nytimes.com/2013/12/09/a-closer-look-at-tornadoes-in-a-heated-climate.

Muller, Richard. 2013. “The Truth About Tornadoes.” New York Times, November 20, 2013. http://www.nytimes.com/2013/11/21/opinion/the-truth-about-tornadoes.html.

Markowski, Paul, Harold Brooks, Yvette Richardson, Robert Trapp, John Allen & Noah Diffenbaugh. 2013. “A ‘Truthier’ Interpretation of ‘The Truth on Tornadoes.’” A letter published in “A Closer Look at Tornadoes in a Human-Heated Climate.” Dot Earth (blog), New York Times, 12/9/2013, http://dotearth.glogs.nytimes.com/2013/12/09/a-closer-look-at-tornadoes-in-a-heated-climate.

U.S. Tornado Climatology, National Climate Data Center, http://www.ncdc.noaa.gov/oa/climate/severeweather/tornadoes.html#history.

Missouri Damage from Severe Weather Increases

MO Damage ChartDamage from severe weather has increased in Missouri, just as it has nationally.

The National Oceanographic and Atmospheric Administration maintains records from 1995-2012 regarding the amount of damage and the number of deaths and injuries from hazardous weather. The first graph at right shows that the cost of hazardous weather damage was relatively small through 2005. It shot up starting in 2006, however, with high peaks occurring in 2007 and 2011.

In 2011, damage cost $3.3 billion – more than 25 times the average yearly amount before 2005. The bulk of it resulted from two tornado outbreaks, one of which hit the St. Louis area, including Lambert Field, and the other of which devastated Joplin. That tornado alone killed 158, injured 1,150, and caused damage estimated at $2.8 billion.

MO Deaths ChartThe second chart at right shows deaths and injuries from hazardous weather. Deaths are in blue, and should be read on the left vertical axis. Injuries are in red and should be read on the right vertical axis. The dotted lines show the trends. The large number of injuries and deaths in 2011 are primarily from the Joplin tornado. In 2006 and 2007, injuries spiked but fatalities did not. The injuries mostly represent non-fatal auto accidents from winter ice storms. The fatalities in 1999 resulted from a tornado outbreak.

The Missouri data covers 15 fewer years than the national data discussed in my previous post. It also covers all hazardous weather, in contrast to the national data, which covered billion dollar weather disasters.

Both clearly show an increase in damages over time, but only the Missouri data shows an increase in deaths and injuries.

Climate change predictions generally forecast an increase in weather extremes. While these two data series conform to that prediction, they are not long enough by themselves to draw conclusions about long-term climatic trends with confidence. Further, the number of deaths and the amount of damage depend on additional factors besides the strength of the severe weather. These include whether it affects developed and populated areas. Thus, for discussions of climate change, the data should be used with caution and in combination with other data.

Sources:

State Hazardous Weather Fatalities, Injuries, and Damage Costs, 1995-2012, Natural Hazard Statistics, National Oceanographic and Atmospheric Administration, http://www.nws.noaa.gov/om/hazstats.shtml#.

In addition, descriptions of specific weather events, if they are large and significant, can be found on the websites of the Federal Emergency Management Administration, the Missouri State Emergency Management Agency, and local weather forecast offices. However, in my experience, the best descriptions are often on Wikipedia.

Billion Dollar Weather Disasters in the United States

US Weather Number ChartBillion dollar weather disasters in the United States have increased dramatically over the last 30 years, according to the annual “State of the Climate” report in the August edition of the Bulletin of the American Meteorological Society.

The first graph at right shows the number of disasters per year. From an average of 1.8 per year in 1980 – 1984, the number has increased almost five-fold, to an average of 8.8 per year in 2008 – 2012. The black line shows the trend over the period.

Damages have also increased: from an average of $15.7 billion in 1980 – 1984 to an average of 67.6 billion in 2008 – 2012. That is more than a four-fold increase. The second graph at right shows the amount per year. The black line shows the trend over the period. Dollar amounts have been adjusted for inflation using the CPI.US Weather Damages Chart

Deaths, however, have not increased, they have declined. The third graph at right shows the number of deaths each year.

The chart of deaths is the least complex to understand, so let’s start there. Weather related deaths occur each year, but large weather-related disasters don’t automatically cause lots of fatalities. There are three large spikes in the number of deaths: 1980, 1988, and 2005. The spike in 2005 was almost entirely from Hurricane Katrina. The other two were from powerful heat waves that caused increased death rates due to heat stress. The trend is toward fewer deaths. US Weather Deaths ChartBecause the decline can’t be attributed to a decline in the number or power of the disasters, I suspect that we have improved our ability to anticipate them, take appropriate protective action, and respond once they do occur.

Damage from the weather-related disasters shows the significant variability from year-to-year. There is a huge spike in 2005; that was the year that multiple catastrophic hurricanes struck the United States. Damage from Hurricane Katrina alone was greater than the total loss for all of 2012 (which included Hurricane Sandy in New York)! The graph shows other spikes in 1988, and 2012. The damage in 1988 was mostly from a drought and heat wave in the eastern and central U.S. In 2012, it was mostly from Hurricane Sandy, but also from a drought and heat wave. While there is a correspondence between the number of disasters and the total damage, it is far from perfect (correlation = 0.41). It depends a great deal on the kind of disaster and where it occurs.

The number of disasters shows the least variability between years, and the most consistent trend.

Since the data has been inflation adjusted, the increase in the number of disasters and the damage they cause are probably not related to inflation. One possible explanation might be that increased development has put more property in harm’s way. This might be especially true in coastal areas that are vulnerable to hurricanes. Another possibility might be that weather extremes are more extreme than they used to be. Although previous posts showed that the number of powerful tornadoes has not increased, heat waves, floods, or hurricanes may have. This data does not say.

The next post takes a look at similar data for Missouri.

Sources:

Smith, A., Sidebar 7.1: Billion-Dollar Weather and Climate Disasters: 2012 in Context, [in “State of the Climate in 2012, Bulletin of the American Meteorological Society, 94, (8), S151. Downloaded from: http://www.ncdc.noaa.gov/bams-state-of-the-climate/2012.php.

Billion-Dollar Events, Billion-Dollar Weather/Climate Disasters, National Climatic Data Center, http://www.ncdc.noaa.gov/billions/events.

The Most Powerful Tornadoes Are Less Frequent

The previous two posts have discussed the occurrence of tornadoes in Missouri and surrounding states, as well as national and Missouri trends in tornado frequency. This post concerns the most violent and destructive tornadoes, the F 3-5 tornadoes.

The amount of destruction a tornado causes depends not only on the strength of the tornado, but also on where it occurs. If it occurs in unpopulated, undeveloped land, the destruction may be less. If it occurs in a heavily populated area, and it if catches people unprepared, the destruction and loss of life may be greater. The last 50+ years have seen a significant increase in population, and a significant expansion of the amount of developed land. Thus, tornadoes are more likely to strike populated and developed areas.

Source: Tornado Climatology page of the National Climate Data Center

Source: Tornado Climatology page of the National Climate Data Center

The graph at right, copied from the U.S. Tornado Climatology web page of the National Climatic Data Center shows the annual number of strong to violent tornadoes in the United States. As has been the case with all of the annual tornado data we have looked at so far, this data varies greatly from year-to-year. However, it seems pretty clear that there is no overall trend toward increasing frequency. In fact, if anything, the trend has been towards decreased frequency – there are fewer highly destructive tornadoes now than there were during the mid-1960s. Who’da thunk it!

Some may take this as a disconfirmation of the theory of global warming. It turns out, however, that an increase in the number of tornadoes was not forecast by the IPCC Fourth Assessment Report or in the most recent two assessments of Global Climate Change Impacts in the United States. These documents all conclude that it is “…difficult to know if and how such events have changed as climate has warmed, and how they might change in the future.” (Global Climate Change Impacts in the United States, Thomas R. Karl, Jerry M. Melillo, and Thomas C. Peterson, (eds.). Cambridge University Press, 2009, p. 11.)

The confusion may arise because these documents did forecast an increase in some kinds of extreme weather events (the intensity of hurricanes, for instance). While all kinds of extreme weather may seem similar, a tornado is a very unique and specific weather phenomenon that may or may not be related to other kinds of extreme weather.

Thus, in summary, the total number of tornadoes reported annually has increased, but almost entirely from an increase in the number of small, weak tornadoes reported. If you eliminate the F-0 tornadoes from the count, the trend is basically flat. And the trend in the most powerful tornadoes seems to be towards decreased frequency.

Sources:

U.S. Tornado Climatology, National Climate Data Center, http://www.ncdc.noaa.gov/oa/climate/severeweather/tornadoes.html#history.

Global Climate Change Impacts in the United States, Thomas R. Karl, Jerry M. Melillo, and Thomas C. Peterson, (eds.). Cambridge University Press, 2009.

IPCC, 2007: Summary for Policymakers. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA..

Tornadoes Seem More Frequent, But They Aren’t

In my previous post, I discussed some statistics regarding tornado frequency in Missouri and surrounding states. In this post, I look at national and Missouri trends over time. Are tornadoes increasing in frequency, or are we just better at spotting them? Are they stronger and more destructive, or are we simply saturated with dramatic video from storm chasers?

All Tornadoes ChartAt first, it might appear that tornadoes have increased in frequency. The first graph at right shows the total number of tornadoes reported since 1950. The blue line shows the number reported nationally, and should be read on the left vertical axis. The red line shows the number reported in Missouri, and should be read on the right vertical axis. There is a lot of variation from year-to-year, but the trends increase dramatically.

However, there are problems. Rain and temperature tend to occur over hundreds of square miles – they can be witnessed even in sparsely populated places, or by remote sensors. On the other hand, a tornado, and the damage it causes, are confined to the path of the tornado on the ground. To witness a tornado, it used to be that someone had to be right there – not likely in sparsely populated lands. Then they had to make a report, which might involve significant delay and travel over many miles. And finally, tornadoes can be hidden by darkness or rain. Thus, many tornadoes may have gone unwitnessed or unreported.

Our ability to witness and report has increased dramatically over the years, however. First, land that used to be empty is empty no longer – more of the land is populated with potential witnesses. Second, cell phones and the Internet greatly increase our ability to report tornadoes. And finally, the National Weather Service has deployed doppler radar, which now covers most of the country. Even tornadoes that escape human witness are seen by the radar. Consequently, many tornado experts believe that tornadoes have not increased dramatically in frequency, but rather, our ability to detect them has improved.

F1-F5 ChartScientists believe that the weakest of tornadoes are the ones most likely to have escaped detection in the past. So one way of trying to determine if the increase comes from more tornadoes or better detection would be to eliminate the weakest ones from the count, the F-0 tornadoes. The second graph at right shows the number of F-1 to F-5 tornadoes, again with the national numbers on the left vertical axis in blue, and the Missouri numbers on the right vertical axis in red. As before, there is tremendous variation from year-to-year. But this time, the overall trends do not appear to be dramatically increasing, they appears to be rather flat.

Thus, it appears that tornadoes are not really increasing in frequency. Rather, our improving ability to detect them seems to be making them seem more frequent.

Source:

Storm Prediction Center WCM Page, National Storm Prediction Center, NOAA, http://www.spc.noaa.gov/wcm/#enso.

Tornadoes In and Around Missouri

In recent years, the news has been filled with dramatic reports of devastating tornadoes. From the Joplin tornado in 2011 to this year’s outbreak in Oklahoma, it seems like every year brings reports of terrible devastation from these powerful storms. Are they getting more frequent, or are we just better at detecting them? Are they getting more powerful, or are we just saturated with dramatic video from storm chasers? I thought it might be interesting to look at trends in the number of tornadoes nationally and in Missouri. In this post I will cover some tornado basics. In the next, I will look at trends in the number of tornadoes over time. In a third post, I will look at trends in the most severe tornadoes.

Tornadoes are most common during the spring and summer, but they can occur any time of the year. Texas is the state that experiences the largest number of tornadoes (half again as many as Kansas, which is second), but it is also the second largest state (after Alaska). If you divide the annual number of tornadoes by the land area of the state, the result is surprising. The table below shows the top states in tornadoes per 10,000 square miles of land area. Missouri is 12th.

State Tornadoes per 10,000 sq. mi. State Tornadoes per 10,000 sq. mi.
Florida 12.2 South Carolina 9.0
Kansas 11.7 Alabama 8.6
Maryland 9.9 Louisiana 8.5
Illinois 9.7 Arkansas 7.5
Mississippi 9.2 Nebraska 7.4
Iowa 9.1 Missouri 6.5
Oklahoma 9.0

The most important tornadoes, however, are the large, powerful ones. The National Oceanic and Atmospheric Administration ranks tornado strength on the Enhanced Fujita Scale from 0-5, with 5 being the most powerful. States with the most tornadoes ranked EF-3 to EF-5 are Kansas, Arkansas, and Texas. But again, if you divide by the state’s land area, you get some surprising results. The table below shows the stop states in EF-3 to EF-5 tornadoes per 10,000 square miles of land area. Missouri is tied with four other states for 8th.

State EF-3 to EF-5 Tornadoes per 10,000 sq. mi. State EF-3 to EF-5 Tornadoes per 10,000 sq. mi.
Tennessee 0.6 Indiana 0.4
Arkansas 0.5 Missouri 0.3
Kansas 0.4 Iowa 0.3
Oklahoma 0.4 Alabama 0.3
Mississippi 0.4 Georgia 0.3
Kentucky 0.4 South Carolina 0.3

Of the 10 most deadliest tornadoes, 3 have involved Missouri. The Joplin tornado, which occurred in 2011, is listed as the 7th most deadly in history. The 3rd most deadly tornado struck St. Louis in 1896. And the deadliest tornado in history was the Tri-State Tornado of 1925. It touched down near Ellington, in Reynolds County, MO. It travelled northeast, crossing the Mississippi River, traveling completely through Illinois, , finally dissipating about 3 miles southwest of Petersburg, Indiana. The total track was 219 miles in length with an average width of 3/4 of a mile. Some 695 people were killed, and 2,027 injured.

Sources:

For national and state tornadoes: U.S. Tornado Climatology, National Climate Data Center, http://www.ncdc.noaa.gov/oa/climate/severeweather/tornadoes.html#history.

For the Tri-State Tornado: 1925 Tri-State Tornado: A Look Back, Paducah, KY National Weather Service Weather Forecast Office, http://www.crh.noaa.gov/pah/?n=1925tor.

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