Really dumb idea
Some Chinese "scientist" proposes building huge north-south walls in Tornado Alley to block the twisters. He thinks tornados are blocked by ranges of hills, so a manmade hill will do the same.

Nope. Twisters do occasionally stay above a valley after sliding up a hill, but occasionally isn't enough to justify the huge expense.

Perfect counterexample from Manhattan. The 2008 tornado came from the southwest, and first smashed a hilltop subdivision. Then it dropped immediately down a steep cliff into Wildcat Valley and smashed an auto dealer and trailer park in the creekbed. No obstacle, natural or manmade, will keep a tornado from eating its favorite snack!

MMMMM! TRAILER!


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There's a smaller-scale example of an actual manmade wall in the part of Enid that I've been focusing on. The 1966 tornado came (unusually) from the NW. It ran into the Union Equity elevators, which are about 150 feet tall. Immediately dropped down and started eating houses at Cherry and 12th.



The twister didn't damage Union Equity; reinforced concrete will resist any natural force. Then in 1992 Union Equity was bought by Farmland Industries and closed down to pay Farmland's hostile-takeover debt to JPMorgan. Now the elevators are abandoned and decaying. Same old story. Unhurt by tornado, smashed by The Chosen.

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Sidenote: The dumbness of the wall idea was known 200 years ago. I happened to post this old story in connection with another question about tornados (How was the sound described before freight trains or jet planes?)... but the story includes a clear indication that the tornado appeared on the side of a hill and descended to a meadow.

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In fairness, there are some 'blockers' that might work better than a wall. If you can get the tornado to pick up some viscous blob-like objects, you could break up its angular momentum. The 'Sharknado' was supposed to be a maximally scary twister, but I think it could be the exact opposite. Seems worth a try anyway.
  ¶ 5:23 AM