SAN DIEGO — The bathtub rings in the reservoirs that hold California’s liquid life have never been more exposed. Shorelines are bare, brown and bony. Much of the Sierra Nevada is naked of snow. And fields in the Central Valley may soon take to the sky. A Dust Bowl? Not yet. Though this drought will surely go down as the worst in the state’s recorded history. Until next year.

But something else is evident in this cloudless winter: when you build a society with a population larger than Canada’s, and do it with one of the world’s most elaborate plumbing systems, it’s a fragile pact. California is an oasis state, a hydraulic construct. Extreme stress brings out the folly of nature-defiance.

The whole fantasy of modern California has long been dependent on an audacious feat of engineering. You could drain the Owens Valley to allow Los Angeles to metastasize. (See “Chinatown.”) You could grab water from Yosemite to keep San Francisco alive. And you could move all that snowmelt up north to the south, and feed the world.

When it works, it’s a marvel. Golden Gate Park is green. Los Angeles has a river (sort of). The fragrance of fruit trees fills Fresno. But what if there is no snow, no rain, and nothing left in the aquifers underground? To date, going back to the start of its water year last July, Los Angeles has received 1.2 inches of rain. Yes, for the year. San Diego will soon notch its driest winter ever. And 80 percent of the state is in extreme drought.