An imposingly large man with a neat mustache, Mr. Remus, 59, grew up in Western Nebraska and speaks deliberately. In his tidy, windowless office in Omaha, the main feature is a tabletop map of roughly half the United States. Over the course of several interviews, he discussed his work and said the Corps had not looked at climate change from a planning perspective.

“Scientists say that, in the Missouri Basin, we’ll be spending more time at each end of the spectrum — longer and more severe floods, longer and more severe droughts,” Mr. Remus said. And this year, he had “nothing but bad options.”

A 2012 report on climate change in the Missouri River Basin, commissioned by the Bureau of Reclamation (the Corps’ western equivalent) predicted by the middle of this century a roughly 6 percent average annual increase in upper-basin runoff and a bit more than a 10 percent increase in the lower river.

The Missouri Basin had more runoff from rain and snow last year than all but two years since record-keeping began in 1898. “Is that normal variation?” he asked, or “are we working our way to a new normal?”

“Something’s changing, what that is exactly. …” he said, trailing off.