Thursday, July 14, 2011

More Thoughts on the Tornado Outbreak of 2011

I've just completed  participating in a conference sponsored by the Geneva Association where I presented my thoughts on this years tornadoes.  In preparing for the presentation, I used our casualty models to see if this year suffered from any of the vulnerabilities we had identified that will inflate fatalities.  The answer to that question is yes.  Compared to previous outbreaks, this one occurred predominantly in the southeast which has the highest fatality rate from tornadoes than any other region.  As an example, the fatality rate for the US is .45 per million calculated using data from 1950-2010.  Mississippi has a fatality rate of 2.8, six times the US average.  Secondly, there is a greater proportion of mobile homes than previous outbreaks.  As a comparison, consider the tornadoes of 1953, the last year we suffered more than 500 deaths.  For the counties affected by those tornadoes, the percentage of mobile homes in the housing stock was 6 tenths of one percent.  It was 10 percent for the counties affected by this years tornadoes.  Our research confirms the observation that you are 10 times more likely to die in a mobile home struck by a tornado than a permanent home.  As more mobile homes are in the path of the tornado, higher casualties will likely follow.  Finally, one third of this years fatalities occurred on a weekend including the tornado in Joplin.  We have found that casualties are significantly higher on either Saturday or Sunday than during the week.  People are safer in the buildings they work or go to school in than they are in their own homes.  I used our casualty model to estimate the change in fatalities for the Joplin tornado if it had occurred on a Monday rather than a Sunday and found the expected fatalities would have been reduced by 23%.

So it's no wonder that we have now exceeded the largest annual death toll since records were kept beginning in 1950.  Or is it that simple?  I also spoke at the AMS Broadcast Meteorology Conference last month.  Some of the comments I heard from people expressed shock at the casualties but also questioning the value of the warnings that have been celebrated for minimizing casualties.  That started me thinking about how I could test whether or not the warnings were effective.  Keep in mind that the Joplin tornado had 24 minutes lead time.  One way to examine this notion is to compare the fatality rate from this years tornadoes with another outbreak.  Again, consider 1953 which had a similar number of killer tornadoes, 41 versus 56 this year, had a similar number of affected counties, 72 versus 75 this year, a similar percent of F-3 plus tornadoes, 78% versus 79% this year, and a similar number of fatalities, 519 versus 537 this year.  The population of the affected counties in 1953 was 3.9 million giving that outbreak a fatality rate of 167 per million.  Affected counties in this years tornadoes is 8.2 million giving this year a fatality rate of 35 per million, half the rate of  1953.  Can the entire difference be attributed to better warnings?  No, I don't believe so, but it is clear that something profound has changed in the last 60 years and the obvious candidate is the investment we have made in our warning system as well as the enhancement in communication technology that we enjoy today.

There is no argument that we have experienced a terrible tragedy.  But it's my belief that the death toll could have much higher if not for the investment by and the efforts of the National Weather Service and the forecasters that have trained to warn residents of the danger of approaching tornadoes.

Thursday, May 26, 2011

How Could This Happen?

            April of 1974 was a very special month for me.  I met, then asked to my senior prom the young woman who has now been my wife of 33 years.  But April of 1974 has a tragic history for it was on April 3, 1974 that hundreds of people died in what was one of the worst days for tornado fatalities.  Since that time, Doppler radar was installed and increased dramatically the accuracy and timeliness of tornado warnings.  Communication technology has improved beyond anything we imagined in the 1970’s and this has allowed warnings to be disseminated quickly and to virtually anyone with a TV, radio, computer or even cell phone.  As a result, casualties from tornadoes have dropped to an annual average of about 60.  Not until April of this year have we witnessed any tornado event which killed more than 100 people.  So it’s not surprising that we are shocked when we see the death tolls from the tornadoes of the last 6 weeks.  For the first time since 1953 we have exceeded 500 fatalities and by the time this season is over, we may top that total of 519.

            Some are asking if we had bad warnings for these storms.  The answer to that question is a resounding no.  Joplin had over 20 minutes of warning and the same has been true for each of the horrific events that our country has endured.  In fact, a good argument can be made that without our current warning technology and the expertise of our forecasters, the death toll would have much, much higher.  It is true that an EF-5 tornado which makes a direct hit on a home is going to kill and injure anyone inside regardless of the lead time these unfortunate souls had before it struck.  But keep in mind, that not all of the tornadoes we have experienced have been that strong and even the ones that were, may not have been that strong for the life span of the tornado. 

            So how could this happen?  Is it climate change or just bad luck?  I am not a climate scientist, so I will leave that question for more qualified researchers.  But I do have some insight into why this year has been one that we will likely never forget.  First, it has been almost 50 years since we have seen an outbreak of this magnitude.  And over that time we have come to believe that outbreaks of this size are so rare that we just don’t consider that they could happen in our lifetime.  But, 50 years is a blink of an eye to Mother Nature.  Our records and oral history only go back a few hundred years at best.  The Midwest was not aggressively settled until the latter part of the 19th century so our experience with tornadoes is limited.

            Secondly, we have increased the population in vulnerable areas dramatically.  Land that was once uninhabited is now crammed with subdivisions.  When my wife and I attended the prom in 1974 the Dallas/Ft. Worth area consisted of 2 counties, Dallas and Tarrant.  It now stretches across 10 counties with a population of about 6 million.  The same can be said for Oklahoma City, Kansas City, Little Rock and other metropolitan areas in “Tornado Alley”.

            Finally, part of the reason is truly nothing more than bad luck.  Even with the increased population, there are still vast areas of rural land.  An EF-5 tornado that plows through a corn field kills nothing more than the fruits of a farmer’s labor.  A financial blow but not a human tragedy.  Tornadoes go where they do and if they cross human settlement, bad things are going to happen.  It is not the act of an angry god but the unfortunate consequence of living with a sometimes violent environment.