The Tornado Damage Risk Assessment Predicting the Impact of A Big Outbreak in Dallas-Fort Worth, Texas

The tornado outbreak in the Oklahoma City area on May 3, 1999 demonstrated just how vulnerable urban areas are to tornado damages. This event did not go unnoticed by the emergency management and severe weather warning community in North Central Texas, just 175 miles to the south. After multiple neighborhoods in Oklahoma were destroyed, many wondered how the Metroplex, an even larger target in tornado alley, would have fared under the outbreak. With the last decade's dramatic growth in spatial analysis computer technology has come an opportunity to create a realistic answer to the question of "What If?".

The North Central Texas Council of Governments and the National Weather Service Fort Worth have put together a "Tornado Damage Risk Assessment" that estimates the results of five (5) different scenarios in which the Oklahoma tornadoes are transposed across the Metroplex. Using Geographic Information System (GIS) Technology, fifty-three (53) tornadoes from the May 3 event in Oklahoma were mapped in a GIS. The actual damage/wind contours from the most damaging tornado ("Moore") in Oklahoma City were imported from engineering surveys. With the largest tornado as the focal point, the group of tornadoes were moved together slightly North-South and East-West across the Dallas-Fort Worth Metroplex in the 5 scenarios - while still maintaining their geographic accuracy in size, speed, and direction. Essentially, the tornadoes were exactly the same, but Dallas-Fort Worth was substituted for Oklahoma City and its surrounding communities.

Appraisal data, land use, demographics, transportation modeling, structure mapping, and aerial photography beneath the tornado paths were processed. The goal was to estimate the region's susceptibility to a major tornado outbreak (using an actual outbreak) and describe the potential toll on buildings, traffic, and people.

The numbers were sobering. As many as 17,000 single family homes, 19,000 apartment, 84,000 residents, and 94,000 employees would be in the direct path of the tornadoes. One scenario would have impacted 400 miles of roads. Somewhere between 1700 and 7700 vehicles will likely be moving across the actual path of the tornadoes as they overtake freeways and arterial roadways. In a congested state (traffic jam), 56,000 - 62,000 cars would fill those same roads. The damage totals reached as high as 38,000 structures and $3 billion.

This paper presents the results of the study for Dallas-Fort Worth Metroplex and promotes the use of GIS computer technology as a means to predict the impact of a major outbreak to a specific urban area. It also explains the implications for the National Weather Service, the North Central Texas emergency management community, and the integrated warning system.