I’ve always been fascinated by tornadoes.  They take on many different shapes and sizes and can be quite beautiful.  But tornadoes are serious business.  Researchers and chasers study them relentlessly.  They have their own reality television shows.  The art and science of predicting where and when a tornado will strike has improved greatly since 1974, but there is still much we don’t know about tornadoes.

I’m sure at one time you’ve seen a traditional “Tornado Alley” map or maybe you’ve seen a map of the U.S. counties most likely to get hit with a tornado.   I wanted to create a map that was more detailed than something at the county level.  I wanted to zero in on precise locations where tornadoes have historically occurred because the past is likely to predict the future.

To start, I located some data provided by the National Weather Service (NWS).  They had a GIS file of tornado tracks from 1950-2006.   Information on the intensity (EF scale), the length and width of the track, property and crop loss estimates, as well as fatalities and injuries were included in the file’s attributes.  In order to quantify the impact of a tornado without including biased data,  I chose two variables  – the number of tornadoes and the intensity of each tornado.  Next, I simply laid out an imaginary 10 square mile grid across the U.S. as a geography for aggregating my data.  I chose a 10 square mile grid because it is usually much smaller than a county (on average you can fit 4-5 grid cells within an average sized county).  I counted each tornado that crossed into a grid cell and summed up the EF scale intensity of each tornado (actually, I added a value of 1 to each storm’s EF number to account for storms with an intensity of EF 0 ).  Each of the data values were normalized before computing a final value for each between 0 and 1.

The results of the exercise can be found here in this interactive map.  Based on our methodology, the part of the country most likely to experience a tornado is located on the Oklahoma and Kansas border – specifically, the the northwest corner of Kay County, OK and the southeast corner of Sumner County, KS:

Luckily, this is not a densely populated area.  In fact, less than 500 people live in this particular cell.  However, the Top Ten Tornado Hot Spots include several areas where the population is high:

As you can see, there are several heavily populated corridors that are historically most likely to experience a tornado.  Oklahoma City (OK), Shreveport (LA), Little Rock (AR), and Jackson (MS) are the most heavily populated cities within our computed danger zone.

If we assume that small changes in the climate over time will not result in dramatic shifts of tornadic activity, then we can safely predict that the areas of high tornadic activity in the past will continue to experience intense, long-track tornadoes into the future.  This knowledge should affect things like building design and cityurban design, disaster preparedness, and insurance rates.

We’ll be posting various maps related to this exercise on our Pinterest site over the next couple of weeks.  Check back from time to time to see what we’ve come up with.

Public and private planners not only have a responsibility to help develop disaster plans – they are some of the best equipped to do so.  Large-scale disaster planning requires professionals to think in terms of time and space – two skills planners are required to employ.  Disaster planning also requires knowledge of who you are planning for.

Here are some demographics for the aggregate area of the Contamination Zones (50 mile rings) to give you an idea of the scale of nuclear disaster planning that needs to take place.

Of particular concern are the young and the population that lives in group quarters.  These population bases are likely to require assistance in the event of a disaster.  They may also require special accommodations.  For example, if you had to evacuate a maximum security prison you are going to need a place to move them to AND a staff that is qualified to manage the prisoners.  Another likely scenario requires tending to the elderly that would be evacuated from nursing care facilities.  Hurricane Katrina taught us that it is not enough to have a plan in place – you need to have multiple plans for different scenarios.

FEMA has posted some nuclear disaster preparedness information that is worth reading.  It is important that each household is acquainted with the plan(s).  However, large-scale coordinated planning at the city, county, state, and national level is critical.  This  is where we’ve fallen short in the past (see Hurricane Katrina).  Effective planning (and execution) is largely a function of leadership.  Those in leadership positions should be capable of managing multiple large-scale plans.

If you would like to read more about disaster planning and disaster recovery, check out the American Planning Association’s disaster planning blog.