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Desert Diary
Climate/Hundred Year Storms


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As developers in the Southwest fill in arroyos, we may hear talk of planning for 100-year storms. Many people, unfortunately including developers, don't understand what that really means, and it may mean scrimping on drainage. In the first place, when we talk of 100-year storms, we are basing this on an estimate—an estimate based on a very limited weather database as to how often severe storms can be expected in an area.

A second point seldom appreciated, though, is that even if such estimates are correct, that does not mean that if we had a 100-year rain 10 years ago that it will be 90 years before another such storm will occur. We might get such a downpour tomorrow or it might be 150 years until the next one. The 100-year bit is an average for over an extended period of time. Just as a .200 hitter in baseball might get six hits in a row, there is no principle that says we can't get two 100-year storms in the same year.
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Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.

Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.