In the Mississippi River town of Hannibal, Missouri, time apparently flies.
In 2013, Hannibal had a 50-year flood, a high-water event only expected once every 50 years. In 2014, it had another 50-year flood. Somehow, the river has reached its 10-year flood stage in Hannibal—which should happen about once a decade—in seven of the last eight years. And if the years seem to be passing with unusual speed, so do the centuries. Hannibal had a 200-year flood in 2008, considerably less than 200 years after an even larger deluge in 1993.
Evidence is mounting that Hannibal’s statistical anomalies have been caused not by glitches in the space-time continuum, but by a combination of floods getting worse and government estimates of flood risks being wrong.
Those estimates of flood severity and frequency come from the long-troubled Army Corps of Engineers, and they determine how high to build levees and floodwalls, where to approve development in floodplains, and who needs to buy flood insurance.
But a new study of major Midwestern rivers in the Journal of Earth Science found that the Army Corps dramatically underestimates modern flood levels, leaving communities consistently underprepared for potential disasters at a time when flood protection is becoming a more urgent necessity. And climate change only seems to be a small part of the problem.