How do you fight a drought when it’s flooding?

California is built upon the great gamble of irrigation. Left alone, much of the land in the Western United States would be inhospitable to teeming cities. But we’re Americans; we couldn’t let the desert stand in our way. More than a century ago, the U.S. Bureau of Land Reclamation began taming the water in the West. It’s been a remarkably successful project. In California, where I live, irrigation has turned largely barren regions into some the country’s most fertile farmland and most prosperous metropolises. We’ve built “the most ambitious desert civilization the world has seen,” Marc Reisner put it in “Cadillac Desert,” his 1986 history of Western irrigation.

I’ve been thinking a lot about “Cadillac Desert” in the past few weeks as the rains fell and fell and kept falling over California — much of which, despite the pouring heavens, seems likely to remain in the grip of a severe drought. Reisner anticipated this moment. He worried that the West’s success with irrigation could be a mirage — that it took water for granted and didn’t appreciate the precariousness of our capacity to control it. “Everything depends on the manipulation of water — on capturing it behind dams, storing it, and rerouting it in concrete rivers over distances of hundreds of miles,” he wrote. “Were it not for a century and a half of messianic effort toward that end, the West as we know it would not exist.”

But what happens to that century of irrigation when the weather changes, as it is now? Experts