Tornado Damage Risk Assessment Dallas-Fort Worth Metroplex A Regional Exercise in Demographic, Environmental, and Urban Analysis February, 2000 Scenario Two Tornado Outbreak Data Centered at –97.00,32.95 WISE ELLIS HUN COLLIN DALLAS DENTON PARKER TARRANT KAUFMAN JOHNSON HOOD SOMERVELL ROCKWALL All figures included in this summary are estimates based upon the best information available at the time of the study. A variety of other variables can be incorporated into future studies or come into play during a real event of this magnitude. Last Update: January 9, 2001 North Central Texas Council of Governments 616 Six Flags Drive, Suite 200, Centerpoint Two P.O. Box 5888 Arlington, Texas 76005-5888
A Regional Exercise in Demographic,Environmental, and Urban Analysis
February, 2000
Scenario TwoTornado Outbreak Data
Centered at –97.00,32.95
K WISE
ELLIS
HUNCOLLIN
DALLAS
DENTON
PARKER TARRANT
KAUFMAN
JOHNSON
H
HOOD
SOMERVELL
ROCKWALL
All figures included in this summary are estimates based upon the best information available atthe time of the study. A variety of other variables can be incorporated into future studies or come
into play during a real event of this magnitude.
Last Update: January 9, 2001
North Central Texas Council of Governments616 Six Flags Drive, Suite 200, Centerpoint TwoP.O. Box 5888Arlington, Texas 76005-5888
North Central Texas Council of Governments/National Weather Service Fort WorthScenario Two - Page 2
Data Analysis and GeographicInformation System Data Compilation
Scott RaeSenior Research Associate
Department of Research and Information ServicesNorth Central Texas Council of Governments
Advisory Group
Jim StefkovichWarning Coordination Meteorologist
National Weather Service Forecast OfficeFort Worth, Texas
Gary WoodallWarning Coordination Meteorologist
Meteorological Services DivisionNational Weather Service Southern Region Headquarters
Bob O’NealDirector
Department of Research and Information ServicesNorth Central Texas Council of Governments
Rocky GardinerManager of Research
Department of Research and Information ServicesNorth Central Texas Council of Governments
Jack TidwellSenior Environmental Planner
Department of Environmental ResourcesNorth Central Texas Council of Governments
Special Thanks for Data Contributions and Suggestions
Greg Stumpf, National Severe Storms LaboratoryTim Marshall, Haag Engineers
Amy Wyatt, North Central Texas Council of GovernmentsAngi Young, North Central Texas Council of Governments
Tamara Schells, North Central Texas Council of GovernmentsArash Mirzaei, North Central Texas Council of GovernmentsMitch Lestig, North Central Texas Council of Governments
Ken Cervenka, North Central Texas Council of Governments
North Central Texas Council of Governments/National Weather Service Fort WorthScenario Two - Page 3
Study OverviewThis study features the use of digitally mapped tornado path information from a realtornado outbreak laid atop Dallas-Fort Worth urban and demographic data. Moderncomputer technology can help estimate the magnitude that the tasks of warning, rescue,and recovery would require. If we make the very likely assumption that Dallas-FortWorth would see comparable damage in the same portions of the tornadoes that causeddamage in Oklahoma, we can then model this same event across the Dallas-Fort WorthMetroplex and assess how susceptible the area is to large tornado damage potential.
Five (5) separate distributions (scenarios) of the same Oklahoma tornado paths aremodeled with the output including:
• The number of structures in the path• Potential dollar damages to structures and contents• Residents living in the path• Employees working in the path• Utility lines in the path• The distribution of land use in the path• Estimated roadway miles and vehicles travelling in the path
The goal is to stress the importance of planning and preparation for the day when thistype of event does occur in Dallas-Fort Worth. A tornadic outbreak like the one inOklahoma would cover an amazing amount of North Central Texas territory, and thisstudy will help quantify that which would be in the way of the storms themselves.
The Tornadoes usedin this analysis weremapped using adistinct delineation ofthe Fujita Scale (F-Scale) damageregions as theyoccurred inOklahoma. The F-Scale corresponds tothe magnitude ofdamage occurring tostructures.
This documentfocuses on scenariotwo of the study. Formore informationabout study
methodology, data, and procedures, please refer to the study summary document.
North Central Texas Council of Governments/National Weather Service Fort WorthScenario Two - Page 4
Scenario Two
A9 (F-5)
G2 (F-3)
B20 (F-4)E6 (F-4)
D4 (F-3)
G5 (F-3)
E3 (F-3)
D3 (F-1)
D1 (F-1)
E2 (F-1)
A6 (F-3)
B18 (F-1)
B3 (F-1)
B17 (F-2)
A3 (F-3)
D2 (F-2)
A12 (F-2)
B16 (F-1)
B9 (F-1)
C1 (F-0)
A8 (F-2)
B10 (F-1)
E7 (F-1)
A14 (F-1)
G3 (F-0)
B8 (F-1)
G6 (F-2)
A13 (F-0)
B5 (F-0)
G1 (F-0)
E4 (F-0)
B19 (F-1)
B14 (F-0)
H1 (F-0)
B13 (F-0)
B7 (F-0)
G4 (F-0)
A1 (F-0)
WISE
ELLIS
HUNT
COLLIN
DALLAS
DENTON
PARKER TARRANT
KAUFMAN
JOHNSONHOOD
SOMERVELL
ROCKWALLDallas
Fort WorthIrving
Plano
Arlington
Garland
Mesqui te
Lewisville
Carrol ltonRichardson
Bedford
Study Area
Scenario two centers the entire outbreak of tornadoes at -97.00,32.95 (long/lat decimaldegrees). This positioning starts the big tornado “A9” near Interstate 35W in northernJohnson County. Following the precise path direction that it did in Oklahoma, the stormmoves through northwest Mansfield, through southern Grand Prairie, across Interstate20, and northeast into Dallas. This alignment of paths produces the lowest damageestimates of the five scenarios, but the damages still approach $800 million. Arlington,Grand Prairie, Mansfield, and Dallas could each lose over 500 single family homes.
North Central Texas Council of Governments/National Weather Service Fort WorthScenario Two - Page 5
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Above: Path of the large tornado “A9” through Tarrant and Dallas Counties. Bold numbers alongthe path indicate the F-Scale rating given to the same portion of the tornado in Oklahoma.
Above: Three-dimensional computer rendering of tornado “A9” path crossing the Trinity Rivernorthwest of downtown Dallas and entering the Stemmons industrial district.
North Central Texas Council of Governments/National Weather Service Fort WorthScenario Two - Page 6
Major Land Uses in All Tornado Paths
Like scenario one, nearly 80% of the tornado paths in scenario two would be made up of vacantland. The damage from the tornadoes can be attributed to less than 20% of their paths. DentonCounty is extremely active in this scenario, but the slight adjustment of the paths to the northwestspares many communities from the direct hits that occurred in scenario one.
The table below provides structure damage estimates for all of the tornado paths. Damages arecalculated based on appraisal data and the Fujita Scale contour in which the structure is located.
Type Total in Path Property Value in Path Potential LossesSingle Family Homes 8790 $1,043,387,374 $499,778,737Apartment Units 3900 $166,885,696 $92,655,150Mobile Homes 1214 $19,587,208 $14,326,747Commercial Properties 361 $286,711,473 $139,740,610Industrial Structures 85 $86,488,667 $43,370,106
North Central Texas Council of Governments/National Weather Service Fort WorthScenario Two - Page 7
Residents and Employees in Path
The table below provides an estimate of the number of persons occupying the structures in thepath of the tornadoes. Numbers are based upon city data for household size, occupancy rates,major employer locations, and traffic survey zone employment data.
Category Total Persons Persons in F-2 orGreater Contour
Persons in F-4 orF-5 Contour
Residents at Home 34030 17706 3469Employees at Work 19131 10062 2103
Estimated Number of Persons OccupyingResidential Structures In the Path of Tornadoes
Fujita ScaleContour
Persons in Homes Persons in Apartments Persons in Mobile Homes
Above: The most significant damage areasas calculated for scenario two. Displayedpoints represent small area locations withtotal damages exceeding $1,000,000. Thesmall areas are no larger than .2 squaremiles and exist entirely within the tornadopath. Their positioning has been generalizedfor the scale of mapping.
North Central Texas Council of Governments/National Weather Service Fort WorthScenario Two - Page 9
Percentage of City Current Single FamilyHousing Units Destroyed By Tornadoes
The table below describes the inventory of single family houses currently existing in several NorthCentral Texas cities, and compares that to the number that would likely have been destroyed inscenario three. The City of Mansfield would experience the largest percentage loss in thisscenario. Grand Prairie also would experience a significant loss of property.
CITYNAME Houses Destroyed(F2 or Greater Contour)
Estimated Number of CurrentSingle Family Units in 1999
Aerial Image Maps Courtesy of VARGIS LLCAbove: Midway along the path of tornado “A9”. This tornado would unleash some of its mostintense strength over the open waters of Mountain Creek Lake. The damage path narrowly
misses the former Naval Air Station, but does return to shore to produce large damage totals.
North Central Texas Council of Governments/National Weather Service Fort WorthScenario Two - Page 10
Population Threat and Losses by Tornado
In scenario two, the big tornado “A9” would produce the largest threat. Tornado “B20” wouldimpact nearly $100 million of property in Denton County – much of it in F-4 contours. Tornado“E6” threatens F-4 damage like it did in scenario one, but its slight shift to the north and westdramatically reduces its potential losses. None the less, it still impacts 367 structures.
North Central Texas Council of Governments/National Weather Service Fort WorthScenario Two - Page 11
Tornado path enhanced in 3-Dimensional computer model of Trinity River Corridor near theStemmons Industrial District. The tornado path is slimmer than earlier in its life cycle, but the
North Central Texas Council of Governments/National Weather Service Fort WorthScenario Two - Page 12
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Above: Areas of estimated damages to single family homes and apartment units exceeding $5million. The estimation is a function of tornado strength, width, and structure appraisal data.
Estimated Traffic in the Path of Tornadoes
Traffic figures for vehicles in the path of the tornadoes are based on NCTCOG transportationmodeling for major thoroughfares through the region. The data is an estimate of road volumesand capacities across more than 21,000 links throughout the metroplex, many of them calibratedto actual traffic count data. The models include estimates for freeways, arterials, and collectors,but do not include local residential streets. The numbers for scenario two are derived from thosemodeling numbers. For scenario two, we are estimating the number of cars that, as a function ofvolume, speed, time, and distance, should be located on the actual roadway pavement in thetornado’s path at the time the tornado overtakes the route. . Hourly traffic numbers provide anestimate of how many cars would actually cross the path during the hour of the tornado’s primaryimpact. Vehicles trapped numbers are estimates of how many vehicles should theoretically beon the roadway in the tornado path when the tornado strikes (under varying traffic levels).
Hourly Vehicles onRoutes Crossed by
Tornadoes
Vehicles Trapped in TornadoPaths at Normal Roadway
Vehicle Volumes
Vehicles Trapped inTornado Paths if
Roadways all Backed Up*101970 *643 39329
* Estimated based on daily modeling totals and hourly multipliers
North Central Texas Council of Governments/National Weather Service Fort WorthScenario Two - Page 13
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Above: Areas with 3 or more vehicles potentially trapped inpath of tornadoes. Region-wide in scenario two, 643 vehiclesare estimated to be in the direct path of tornadoes under suchnormal flow conditions. Each dot represents an area of nogreater than .2 square miles. The dots represent a total of allmodeled road data in those small areas. Note that thenumber of cars “trapped” is also dependent upon the width ofthe tornado path.
Above: Areas with 100 or more vehicles potentially trapped intornado paths if roadways backed up (traffic jam). If all laneswere backed up with an average of one vehicle per 35 feet, theabove areas would find large numbers of vehicles located in thepath at the time of the tornado strike. If all of the modeledroutes were backed up this way, 39,000 vehicles would be inthe path of tornadoes. Each dot represents an area of nogreater than .2 square miles. The dots represent a total of allmodeled road data in those small areas. Note that the numberof cars “trapped” is also dependent upon the width of thetornado path.
