PHILADELPHIA, Pennsylvania - A physicist with Temple University says three 1,000-foot high walls built in the Midwest would diminish the tornado threat in Tornado Alley.

Dr. Rongjia Tao proposes building one east-west wall along the state line of Kansas and Oklahoma, and two other located in North Dakota and along the state line of Louisiana and south Texas.

USA Today reports Dr. Tao will present his research next week at the annual meeting of the American Physical Society in Denver.

Dr. Tao says the walls would need to be about 150 feet wide.

Dr. Tao says because there are no west-to-east mountains in Tornado Alley to weaken the air flow, collisions between warm and cold air create turbulence and supercells that spawn tornadoes.

Dr. Rongjia Tao estimates the costs of building the walls to be about $60 billion per 100 miles.

His proposal is drawing criticism from several experts, who say it lacks merit.