When Gov. Jerry Brown of California imposed mandatory cutbacks in water use earlier this month in response to a severe drought, he warned that the state was facing an uncertain future. “This is the new normal,” he said, “and we’ll have to learn to cope with it.”

The drought, now in its fourth year, is by many measures the worst since the state began keeping records of temperature and precipitation in the 1800s. And with a population now close to 39 million and a thirsty, $50 billion agricultural industry, California has been affected more by this drought than by any previous one.

But scientists say that in the more ancient past, California and the Southwest occasionally had even worse droughts — so-called megadroughts — that lasted decades. At least in parts of California, in two cases in the last 1,200 years, these dry spells lingered for up to two centuries.

The new normal, scientists say, may in fact be an old one.

Few experts say California is now in the grip of a megadrought, which is loosely defined as one that lasts two decades or longer. But the situation in the state can be seen as part of a larger and longer dry spell that has affected much of the West, Southwest and Plains, although not uniformly. “The California drought is kind of the latest worst place,” said Jonathan Overpeck, a director of the Institute of the Environment at the University of Arizona.