December 30, 2011

Was the Joplin Tornado the Deadliest We Can Expect?

Filed under: Severe — Erin @ 10:58 pm

Meteorologists and weather-watchers are bidding the year 2011 a less-than-fond farewell.  While it was certainly a banner year from the point of view of storm chasing—6 EF-5 tornadoes, 17 EF-4s, and many of them highly photogenic, as the dozens of home videos on Youtube illustrate—it was a catastrophe in terms of the human impact.  With 552 fatalities, this year is tied for the second-deadliest tornado year in the U.S.  The death toll is an order of magnitude greater than even most of the “bad years” of the 1975-2010 period.  Two events are primarily responsible for this:  the April 27 Dixie Super Outbreak, which killed over 300 people (breaking the 1974 Ohio Valley Super Outbreak’s grim record by a hair), and the Joplin, MO EF-5 tornado, with approximately 160 fatalities.

With the 2011 Super Outbreak, meteorologists are starting to work out an approximate historical return period for these large-magnitude events.  Before the 1974 event, the last comparable event occurred in 1936, with an outbreak popularly known as the Tupelo-Gainesville outbreak for the violent tornadoes that occurred in Mississippi and Georgia.  It seems that these huge events occur approximately every 35-40 years.  Obviously, a comparable event could occur next spring, but statistically, it seems that they are a 35- to 40-year event.  And, given that the 1974 Super Outbreak and 2011 Super Outbreak saw comparable death tolls, I think we can also estimate what the human toll for such an event will unfortunately be as long as the affected communities have unsuitable safety options for EF-4 and EF-5 tornadoes.

The Joplin tornado is a different beast.  We do not have a comparable modern event.  Individual tornadoes in 1953 killed over 100 people in Waco, TX and Flint, MI, but that year was something of a catalyst of public outrage, for a third tornado in Worcester, MA killed 94 people.  Public sentiment that year was essentially, “DO something so that this never happens again!”  And for 57 years, no single tornado in the U.S. did kill over 100 people.  Then… it happened again.

Was the Joplin event a worst-case scenario?  Is this the deadliest (give or take) that a single tornado can actually be now?

I think the answer to the first question is a guarded “yes,” at least for the specific case of a tornado striking a city.  The tornado was about as strong as they come; its winds were estimated to be up to 250 mph.  They can get more intense than that, but it doesn’t make a lot of difference in terms of structural damage.  The tornado rapidly intensified precisely as it entered the heavily populated regions of Joplin, and it passed right through residential and commercial shopping areas—the worst areas it could strike.  Examination of the track shows that there was also a pretty large corridor of EF-4 and EF-5 tornado damage, which would be expected for a wedge tornado.  Sometimes the area of violent damage is comparatively small, but this was not the case with this tornado.  Storm cellars were rare in this area, making survival above ground mostly a matter of good luck.  The tornado was also rain-wrapped for much of its existence.  In terms of the storm’s power and the location of impact, you can’t get much worse than this.  However, I should note that it occurred on a Sunday.  Some have argued that if it had happened at the same time of day on a work day, it could have been worse.  We don’t know for sure, and let’s hope we don’t find out.  I tend to think it probably would not have been much worse, given that residential areas (not a likely area for commuters to be stranded) and the shopping district (which probably would get more foot traffic on weekends than work-week afternoons) were such a large part of the damage zone.  In my opinion, the Joplin tornado was essentially a worst-case scenario for a tornado striking an urban area.  A comparable tornado striking an urban area probably would have a comparable human toll.

Unfortunately, the second question—is the death toll of ~160 the highest we could see for a single tornado in the modern era—has a different answer.  There are two ways that a single tornado could kill a lot more people than that.

One is the possibility of a weak, poorly-built or dilapidated high rise building taking a direct hit from a violent tornado and collapsing with a lot of people inside it.  Generally, these buildings are not supposed to collapse even in EF-5 events.  Images of collapsed high rises on hurricane landfall sites are misleading; these buildings mostly had shallow foundations and were undermined by the storm surge.  They were not blown over by wind alone, and storm surge is obviously not a factor for tornadoes.  The St. John’s Hospital building in Joplin took a direct hit from the tornado when it was at EF-4 intensity and it did not collapse.  However, a poorly-constructed or dilapidated one could.  (As an aside, one does have to wonder about the possibility of a tornado tearing up ground several feet deep, as happened in the EF-5 tornado on April 27 in central Mississippi. This could definitely undermine a slab foundation on a house, resulting in the foundation being ripped from the ground—the supposed hypothetical “F6 intensity” signature that one heard bandied about prior to the adoption of the Enhanced Fujita Scale.  However, high-rise buildings have much deeper foundations than residential homes.)

The other possibility is that of a violent tornado striking a crowded spectator event, such as a sports game, a fairground, a speedway, etc.  This possibility has been discussed at length by meteorologists such as Dr. Roger Edwards of the Storm Prediction Center.  It’s almost happened before, in fact; in 2008 an EF-2 tornado in Atlanta, GA struck the Georgia Dome while a basketball game (involving my college team) was going on.  It had gone into overtime, so people were not milling around outside.  Still, there are videos from that event of pieces of the roof collapsing and falling to the floor while the spectators were left to fend for themselves in the stands.  A stronger tornado could very easily have taken that roof off.

So yes, although the Joplin tornado was very likely a worst-case event for a tornado strike on a city, thereby representing an approximate limit on fatalities for that type of disaster, the potential exists for individual tornadoes to kill far more people than that in a different sort of disaster.  Let us hope that we can deal with the infrastructure and the safety considerations of large venues so that these greater disasters do not occur, either in 2012 or years to come.

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October 19, 2011

NWA 2011: Thoughts About Tornado Warnings and the Casualty Count

Filed under: Severe — Erin @ 7:56 pm

I attended the National Weather Association’s conference in Birmingham, Alabama, for two days.  Toward the end of the second day, the main focus of the talks was the terrible death count from tornadoes for 2011, and most of the speakers were coming at the problem from the perspective of social science such as psychology.  It is understandable that people would want to better understand what happened in an anomalous, outlier year such as 2011.  It is understandable that people would want to find out if the catastrophe was a result of factors that can be easily changed, and that they would even be biased toward that hypothesis.  (One presentation even mentioned the “optimism bias”—a concept that seems a bit strange to me as a natural pessimist, but I can readily see that it would exist in most people, and I would say that this is a perfect example of it.)  My intention here is not to call anyone out.  However, I think that a lot of the research is, frankly, barking up the wrong tree.  There are also some very serious flaws with some of the studies themselves.

The bulk of the research involved surveys of people from the areas that were impacted by tornadoes in 2011.  The surveys contained questions about NOAA watches and warnings (whether people received them, how they received them, whether they were understood) and people’s responses to these messages.

Here are some points I took away from the social science presentations:

  • An overwhelming majority of people in impacted areas did receive warnings.
  • A very small minority of them immediately went to shelter after receiving a warning from the first source.
  • A rather large plurality sought out additional information from TV, the Internet, or personal confirmation to determine if the tornado actually existed and would potentially affect them.  This was more likely in people with higher levels of education and in people who knew more about the weather.  (I would like to note here that this is exactly what I did when the east-central MS EF-5 tornado of April 27 was heading my way.  I did not immediately barricade myself under the stairs when I heard the warning.  I looked at radar to identify a probable debris ball signature and plotted its projected path to go right over my house.  I then grabbed my cat and got out of town.  The tornado lifted, but if it had stayed on the ground, I could have been killed as a result of following the canned advice rather than reasoning out the best course of action for myself!)
  • A minority of people chose to completely ignore a warning.
  • When asked how likely they, personally, thought it was that their area (of what radius?  I don’t recall if it was stated) would be significantly impacted as a result of bad weather mentioned in a warning, the most common answer was less than a 25% chance.  The social scientists said that they wanted people to guess a nearly 100% chance, but in fact, the scientifically and statistically correct answer was less than 5%.  Interestingly, this arguably refutes the “optimism bias” argument in that people did give a more pessimistic judgment of their risk level than was really the case, just not pessimistic enough to suit the social scientists.

The social scientists seemed to be dismayed by the fact that people were less likely to immediately dive for cover the more educated and weather-savvy that they were.  Needless to say, this is an odd message to deliver to a room full of meteorologists (many of whom actively seek out bad weather in their vehicles).  What is the point here?  “Ignorance is strength,” to quote from Orwell? Let alone that people can’t exactly become less weather-savvy, less educated, or more paranoid about the personal impact from a storm if they already know better.  This is an example of trying to close the barn door after the animals have escaped.  These things are what people do, and with the proliferation of web phones with more and more features that allow people to have access to information virtually anywhere, these behaviors are only going to become more common.  This means that they are the behaviors that must be worked with and planned for.  Trying to force people into a state of unnecessary and statistically unwarranted fear is not going to work.  Nor is it a good idea to try to bully people into not seeking out information and using cognitive reasoning.  I’m no social scientist, but I can tell you that if this is attempted, the most likely reaction is a rebellious contempt for “the government” for “trying to make us not question, not think for ourselves, and do as we’re told.”  I would be just about willing to guarantee it.  It could backfire badly.  People ultimately have to be responsible for their own decisions.

Furthermore, there was absolutely no evidence given that people who sought out more information first were more likely to be injured or die in an event, and obviously the survey methodology required interviewing people who did not die.  Knowledge about what the people who died did must come from people who were with them and survived.  However, I never even saw that there was a distinction made between the group of people who were in the path of the tornado and were uninjured or had only minor injuries, and those who were severely hurt or killed.  It would have been useful to find out if the people who were severely harmed did anything differently from those who were more or less okay.  Given that at least one of the surveys was conducted via e-mail shortly after the event in question (the Tuscaloosa tornado), I would expect that there would be very few people who were severely injured who even participated in it, because they would have been in the hospital.  In effect, the social scientists gathered statistics about a control group and presented it as though it represented the experimental group.  In this situation, the statistics about behavior patterns following a warning mean nothing in themselves.  There is nothing (survival/non-survival, minor/major injury) to correlate them to.  Implying that these behaviors caused the death toll to explode is unsupported speculation.  The one survey I saw that definitely interviewed people who had lost loved ones or who were severely injured was conducted in Smithville, MS, and these authors did not make any wild inferences about how seeking out additional information had led to the deaths.  There is simply no data support for it.  The only situation where it might make a difference is when the lead time is basically zero and every second counts, which was not the case in the April 27 tornadoes or the Joplin tornado.  (I had a lead time of about 25 minutes, which was enough for me to get my cat and laptop and go 18 miles away.)

There was one data omission that is, in my perspective, more important than any behavioral survey.  One table that I did not see in any of the social science presentation was this one:

F Scale Killer Tor Fatalities
F0 1 1
F1 3 4
F2 15 24
F3 23 76
F4 13 160
F5 6 282
F? 0 0
TOTAL 61 547

(Credit to the Storm Prediction Center: http://www.spc.noaa.gov/climo/torn/fataltorn.html)

That is, 95% of all tornadic deaths this year occurred in EF-3 or higher tornadoes, which will destroy most or all walls in a house.  EF-5 tornadoes can even expose the basement and descend into it (it is a myth that the funnel would magically stop at the ground level if an open hole existed for it to twist into), sucking people to their deaths.  And it gets even more significant when you dig deeper into the data.  A look at the list at the top of that page shows that only 4 of the deaths from EF-2 or weaker tornadoes occurred in permanent houses.  I don’t know exactly what happened there, but it could have been extremely bad luck such as a tree falling on the house, a piece of heavy furniture, or a piece of timber causing injury.  It could have been a weak structure.  The point is, this is very rare.  The rest of the deaths in EF-2 and weaker tornadoes were in trailers, vehicles, outdoors (all highly dangerous places to be in a tornado) or were unknown.

I respect the research into this year’s terrible tornado casualty count.  It is important to determine exactly why this occurred, and one question that did need to be answered was whether it happened because of bad decisions.  This is the question that the social scientists have attempted to answer.  I simply disagree very strongly with their apparent conclusions, as I think they are unwarranted by the questionable research methodologies, and are little more than speculation.  My contention is that the catastrophic death toll is directly attributable to major, violent tornadoes, the kind that obliterate entire homes, happening to occur in a lot of populated areas this year.  In short, it was a statistical outlier year.  This classification does not address the underlying structural problem of the Southeast, which is that effective storm shelter is not commonly available for the most violent events, but that’s not an easy problem to resolve.  Unfortunately, in my opinion, it is this hard problem, rather than comparatively easy ones regarding bad decisions, that must be answered if this type of death toll is to be prevented from ever happening again.

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May 26, 2011

What’s Going Wrong?

Filed under: Severe — Erin @ 9:23 pm

This year has had a truly terrible human toll from tornadoes. The current fatality count, approximately 500, is an order of magnitude larger than the average for an entire year. It is to be hoped that this number does not substantially rise, but we do have June, the tropical season (which is expected—and I agree—to be quite active and have a higher than average risk of U. S. hits), and the cool-season secondary severe weather peak. However, this figure is horrible enough even if these periods of higher risk produce absolutely no damaging or fatal tornadoes. Something went very wrong this year, something that has not gone this wrong in almost 60 years, and it is important to determine what it was.

Having followed the stories in a fair amount of depth and from multiple sources, I have developed some suspicions of my own about what some of the problems were. These are problems that either appeared in multiple situations or that appeared in sites where high concentrations of deaths occurred. Other people may form their own opinions, but in whatever analysis of 2011 that takes place (and you can just about guarantee that something of the kind will be done), I hope that the following issues are seriously examined.

1. Safety recommendations for urban residents.
One ugly lesson we have had forced on us this year is that, contrary to long-standing myth about cities being safer than rural areas in tornadoes (perhaps because of the idea that buildings will provide resistance?), a city may well be the worst place one can be in a violent tornado. Even in the age of high-resolution Doppler radar, real-time chaser and spotter reports, live coverage, and 20-minute lead times for warnings, we now know that an EF-5 tornado striking an urban center can result in a triple-digit death toll, as happened in Joplin, MO. It is easy, in retrospect, to understand why a densely packed urban area may be the worst possible place to be. Other than high-rise office buildings, there is no safe place to be. High-rises, according to the EF-scale, will not be demolished even in an EF-5; the maximum expected damage is “permanent structural deformation.” However, directing everyone to the nearest tall office building is a ridiculous “safety” recommendation, needless to say.

What are some other problems with urban areas? Many buildings in the central business district, like fast food restaurants and small businesses, are not constructed to withstand anything like a tornado, and they are simply not safe places to be. Big box retailers will contain very heavy stock that is piled high, providing plenty of potentially deadly missiles. Vehicles are everywhere, and they will become airborne. Designated tornado shelters, which some communities do have, would be useful only if people flocked to these sites well in advance of an actual tornado, because congestion on the roads could result in mass fatalities. Storm cellars would be all but nonexistent, and basements are limited in spatial extent and would be directly beneath the houses, which puts anyone taking shelter therein at risk of exposure to tornadic winds and suction if the house is removed. There is no easy way to get out of danger; traffic congestion will occur if people try to evacuate en masse, putting people in possibly even greater danger than they would have been if they had stayed put. And, of course, cities will have more debris than any other type of community.

We need to seriously consider what kind of safety recommendations can reasonably be given to people who live in town—if any. It is highly uncommon for cities to be struck by EF-4 and EF-5 tornadoes, but it can happen, and the buildings do not provide friction-based wind resistance that would mitigate the effect of violent winds. The situation needs to be looked at to see if any sort of useful specialized safety advice can be given to urbanites.

2. Vulnerability of cell phone networks.
Sometimes when tornado victims are quoted in the news as saying “there was no warning,” what they mean is that they, personally, were not aware of the situation. However, every fatal tornado this year except for one occurred within a tornado watch (link), and that one, an EF-3, occurred within a severe thunderstorm watch. I do not want to sound callous, but there is a responsibility to be weather-aware, which includes awareness of tornado watches and warnings. The outbreaks were all extremely well forecast. Most warnings this year had lead times of 20 minutes or so. In these situations, it is simply inaccurate to say that there was “no warning.” It is passive-aggressively blaming the Weather Service for one’s own failure to be aware.

However, in some cases, there was a legitimate lack of warning, though this is not the failure of the Weather Service. These instances involved the failure of the power grid and the cell phone network, taking down any means by which one might receive weather warnings other than a battery-powered or hand-crank radio. This occurred in some of the small towns that were overrun by the extremely violent EF-5 tornado that traversed northwest Alabama on April 27. I think it also occurred in one of the EF-4 tornadoes of the same day. This is a real problem. Most new phones have the ability to function as handheld PDA, music player, portable gaming device, organizer, Rolodex, e-mail, Twitter, Facebook, and even web browser. With this kind of capability—and none of it dependent on a steady AC/DC power supply—it is easy to understand why people would be reluctant to buy a portable radio. They depend on their phones, and with good reason. However, the cell phone network is clearly vulnerable. If there is significant damage to a tower, down the network goes. This goes for other disasters, including terrorism. The problem needs to be examined to see if these towers can be made more robust. Severe weather outbreaks usually have more than one round, and areas that saw their power and communications knocked out by one (even relatively benign) event can be extremely vulnerable later on.

3. The DTV conversion.
I had a bad feeling about this as soon as the DTV changeover began back in 2009. With the old analog signals, one could have a fuzzy screen—even no visuals at all—and still have audio. With the digital signal, the broadcast becomes choppy, and before long it goes completely black and silent. You have either a near-perfect picture or you have nothing. I have heard more than one anecdote of people in tornado-struck areas who did not lose power until after the tornado hit, but who could not hear the warnings because their TV signal had gone out. I don’t know how many fatalities, if any, were caused by this, but it is a problem that, in my opinion, was severely underrated when the rush to DTV was taking place.

4. Dangerous amateur videography.
There are a lot of videos out there of this year’s tornadoes, and a great many of them were not taken by experienced storm chasers or always-running security cameras. They are also not all taken by people who were a safe distance away from the tornado. One tornado video from Alabama was shot by someone who had a car accident while taking the video! This is a major problem. There is not one thing that can legally be done to stop people from taking video of approaching tornadoes if that is what they want to do, but it is a sad reflection on our society. I don’t blame storm chasers for this. Responsible storm chasers and weather spotters have provided a lot of on-site reports, helping newscasters and people following the situation online know when there is actually a confirmed tornado. Real-time reports of a tornado on the ground helped me decide to evacuate in advance of an EF-5 tornado. Some storm chasers behave highly irresponsibly on the road, and they should be condemned by the rest of the community for it, but overall these people take their hobby very seriously. The videos I speak of are taken by people who just happened to see the tornado and decided it would be a cool idea to get video of it, and the videographers clearly have no knowledge of how far away they should be or where to go if the tornado shifts its path. This particular trend is not the fault of storm chasers; it was produced by social media culture.

5. Lack of shelter from violent tornadoes.
The overwhelming majority of this year’s fatalities have occurred in violent tornadoes, those rated EF-4 and EF-5. This is because these tornadoes will utterly demolish well-built houses, leaving only a pile of debris over a foundation (EF-4) or a bare foundation altogether (EF-5). The Hackleburg, AL EF-5 tornado even buckled the concrete slab foundation of one structure, and the Neshoba County, MS EF-5 (“my” tornado) dug up dirt two feet deep. I think that the odds of survival in these tornadoes are still better than 50-50, but it is easy to see how this kind of situation is incredibly dangerous. The unfortunate fact is that a majority of houses in the South and Midwest do not have basements or storm cellars. My position is that storm cellars are preferable to basements, especially if they have a “fallout shelter” design in which the entrance is not directly above the main room, but is horizontally removed from it. I have read enough accounts of people who took shelter in their basements and were sucked out that (while I agree that basements are clearly preferable to any above-ground shelter) I cannot equate basements and storm cellars. I would also recommend firmly anchored handrails in the main room, in case the door was torn away. The opening sequence of Twister is not myth.

I definitely do not equate above-ground saferooms with underground shelter. These structures are engineered, yes, but they are highly vulnerable on two counts. One, if they are undermined from below, they will roll. Two, the engineering is based on a typical flying missile the size of a 2×4 and a typical flying missile speed of 100 mph. EF-5 tornadoes have wind speeds upwards of 200 mph and have even been clocked as high as 300 mph, though it is a matter of debate whether a large object would travel at these extreme speeds. However, these large objects do travel. In Smithville, MS, the town water tower was dented 120 feet above the ground by a car that became airborne. This is known for a fact by matching paint from the tower and the car. There is video on the Internet of a Canadian F5 tornado in which a whole house is clearly airborne at a great height before it disintegrates.

It’s easy to say, of course, that everyone should have an underground shelter. It is quite another to bring that about. I am opposed on principle to any government mandate to protect people from themselves if there is no risk to other people. This must be a matter of personal responsibility. However, I am in favor of rewarding the decision to install a storm shelter with a tax rebate or credit.  Such credits have been offered in the past, usually to specific regions after particularly high-profile and destructive weather events; I argue that they should be permanent and universal.

These are my suggestions about what should be looked into when the year 2011 becomes part of history, or when people begin to examine what has gone wrong with severe weather preparedness, whichever comes first. Undoubtedly other people will focus on other things. One thing is for certain: We need to know whether this year’s atrocious human toll was in any way preventable, because if it was, it must not be allowed to happen again.

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