More than one hundred years ago, in 1897, spring melt from heavy snowfall caused an enormous three-week flood of the Red River near Fargo, North Dakota. Farmers awoke hearing the terrible cries of animals trapped and drowning in their barns. People escaped by climbing into boats from the second-story windows of homes being demolished by the fast-moving floodwaters. Fargo had sidewalks made of wooden blocks, which all washed away. After the flood, town leaders surprised many by turning down government offers of help and rebuilt the town in the same place. Citizens even retrieved the wooden bricks from upriver, dried them out on the riverbanks, and put them back in the sidewalks.

Exactly one hundred years later, in April 1997, the Red River flooded again. This time, the National Weather Service had warned people in early March that flooding was likely because of extremely...