U.S.A. Tornadoes have long tormented the Midwest with intermittent but deadly intrusions. The Great Plains have ideal topography for tornadoes, allowing cold air from the north to mix with warm winds from the south, leading to a dangerous combination. As a result, Tornado Alley, as it is often referred to, gave rise to over 7,000 thousand tornadoes between 2007 and 2012 alone. These storms have the potential to create millions of dollars of damage and take hundreds of lives, making them a pressing concern for most meteorologists.
However, Rongjia Tao from Temple University has proposed an impressive solution for this important problem. Tao, a physicist with a doctorate from Columbia University, recently published an article in the International Journal of Modern Physics B (IJMPB) suggesting that a series of ‘great walls’ could be built in the Midwest to calm these destructive forces.
Tornadoes form on the Great Plains when cold air sweeping down from Canada meets warm air currents rising from the Gulf of Mexico. When the air meets, the cold air is pushed under the warmer current, creating a horizontal rotation. Under the right conditions, an updraft can force this rotation skyward creating a vertical column of spinning air, or a tornado.
Tao’s walls are designed to stop the mixing of cold and warm air on the ground. He cites similar meteorological climates in Western China and notes that the Midwest has more tornadoes than this corresponding region. The difference lies in the topology; Western China has intermittent hills and small mountains that block the mixing of air, whereas the Appalachian Mountains and the Rocky Mountains act as bookends to a wide, flat plain.
As such, Tao has modeled his walls on the hills in Western China, hoping to replicate the blocking effect. To be successful Tao believes the walls need to be at least 300 meters high (about 1,000 feet), 5 meters wide and as long as possible. The wall can be thought of as the diameter of a protective circle; it’s only effective as far as it stretches. He estimates that building 300 feet of a wall of this size will cost about $160 million, which is relatively little compared to the millions in damage a devastating storm can cost.
But the cost to cover the area Tao is suggesting would be astronomical. Tao would ideally have a wall running East-West across North Dakota, another in Oklahoma and a third in Texas or Louisiana. This would offer the maximum protection from tornadoes, but Tao admits that it would change the climate to some extent.
In an email interview with Tao, he explained how he developed this idea, and what he hopes to see as a result:
I see that you compare the United States Great Plains to the topography in central China. Did you make this comparison after considering building the wall or did the comparison lead you to this proposal?
Rongjia Tao: The comparison led me to my proposal to build the wall for Tornado Alley.
In China hills and mountains block the mixing of air, rather than a wall. Would the shape of the wall impact the desired effect (ie entirely vertical rather than a gradual incline)?
In reducing the wind speed, the vertical height of the hills plays the most important role, while the hill slope plays a minor role. The hill slope will further reduce the wind speed, but not very much. In my paper, my calculation shows that if we can reduce the wind speed to 15 miles/hour or lower, the chance to develop major tornadoes is eliminated. Therefore, the wall shape will work and we do not need incline slope.
As you say in the article, it would be difficult to build such a big wall in one project, so it would be better to start out with smaller walls. Where do you think these initial walls should be placed?
We can start from the areas with very high tornado risk, such as Joplin, MO and Moore, OK.
Do the effects of climate change have an impact on the placement of the walls or their effectiveness?
With the global warming, in long term, the tornado threat will get worse. This is based on the following physics: tornadoes start from turbulence-vortex. With global warming, the air kinetic energy gets higher, i.e. the average wind speed gets higher. Therefore, in the long term, there will be more turbulence-vortex, which will lead to more violent tornadoes. This indicates that the major tornado threat in Tornado Alley will get worse in the long term. I have the above lines in my paper. My point of view is consistent with the reference you mentioned.
Of course, on the short term, the tornado activities will fluctuate year by year. This is the same as the winter weather. For example, from 2000 to 2012, the winter in Philadelphia was getting warmer and warmer. However, suddenly, the 2013 winder was very cold here, colder than any winter in last 30 years.
The wall will remain effective in spite of the global warming. Especially as we already realize the situation, we will consider this factor when we build the wall.
What socioeconomic consequences do you foresee if these walls were to be built? Would those that are less fortunate be forced to live outside the safety of the wall?
Once the wall is built, the major tornado threat will be eliminated in the wall’s protected area. Once people see the fact, they will extend the wall to cover more areas.
What do you hope to see happen after publishing this article?
I hope that my paper will lead to more research and convince people that we can eventually eliminate the major tornado threat in Tornado Alley. Afterwards, I hope that we will select one high tornado risk area to do a field test, building a local wall there to verify that the major tornado threat can be eliminated by the wall. Once this field test is successful, the wall will be gradually extended to eliminate the major tornado threat for the entire Tornado Alley.
The great walls Tao has suggested would be a massive undertaking. But perhaps, if we start gradually we could lessen the tornado threat in the midwest. While the concept seems too big to consider at first, it opens a dialogue addressing one aspect of global warming and serves to better protect the people who call Tornado Alley home.