Tornadoes seek high ground, do more damage going uphill

A study of the effect of terrain elevation changes on a tornado's path shows tornadoes cause more damage going uphill than downhill, U.S. researchers say. Engineers at the University of Arkansas analyzed Google Earth images of the massive 2011 Tuscaloosa, Ala., and Joplin, Mo., tornadoes, discovering similarities between the two in behavior and interaction with the terrain, a university release reported Tuesday. "We wanted to understand the impact of terrain on damage magnitude and tornado path," civil engineering Professor Panneer Selvam, said. "Information about this interaction is critical. It influences decisions about where and how to build, what kind of structure should work at a given site." The analysis yielded three major observations of tornado behavior, they said: -- Tornadoes cause greater damage when they travel uphill and less damage as they move downhill. -- Whenever possible, tornadoes tend to climb toward higher elevations rather than going downhill. -- When a region is surrounded by hills, tornadoes skip or hop over valleys beneath and between these hills, and damage often occurs only on the top of the hills. The 2011 Tuscaloosa and Joplin tornadoes were two of the most deadly and expensive natural disasters in recent U.S. history. The EF4 Tuscaloosa twister in April killed 64 people and caused $2.2 billion in property damage; one month later, the EF5 Joplin tornado damaged or destroyed roughly a third of the city, killed 158 people and caused $2.8 billion in damage. The researchers say their finding of the elevation changes' effects on the two incidents likely apply to all tornadoes and could help prevent the loss of human life and damage to property in future tornadoes.