California’s Ongoing Drought Is Its Worst in 1,200 Years

Tree ring records unveil the severity of California’s drought

Matt Hoover Photo/Corbis

It rained in California last week, a touch of relief in a long dry spell. But a few inches of rain after years of sub-optimal conditions is nowhere near enough to break the state's epic drought.

For three years, the vast majority of California has been affected by drought. Reservoirs are running low, while groundwater stores are falling even faster. Normally snow-capped mounts are mostly bare, and residents, farmers and industry are suffering.

A new study by a pair of scientists has unveiled just how bad California's current drought is. According to researchers Daniel Griffin and Kevin Anchukaitis, this drought is unprecedented in at least the past 1,200 years.

It's common in California for droughts to persist for three years, they write. But using tree ring records of historical precipitation the scientists calculated that the current drought is “exceptionally severe in the context of at least the last millennium.”

Every year a tree lays down a new ring of growth. In years with abundant water trees will grow more, while in conditions of drought trees will grow less. By examining a trees' rings, then, scientists can get a relative estimate of how wet or dry it was during past growing seasons.

In their investigation the scientists “identified 37 droughts that lasted three years or more, going back to the year 800,” says Bloomberg. “None were as extreme as the conditions we’re seeing now.”

There have been years with a dearth of rainfall comparable to the current drought, says Paul Rogers for McClatchy, but the combination of high temperatures and low precipitation is what makes the current drought really stand out. “In terms of cumulative severity,” write the scientists in their study, “it is the worst drought on record (-14.55 cumulative [Palmer Drought Severity Index]), more extreme than longer (4- to 9-year) droughts.”

Though the rainfall shortage behind the current drought fits within the realm of historical variability, the authors note that, in the future, that likely won't always be the case.

"This kind of drought is what we expect to see more of in the future," said Griffin, one of the scientists, to McClatchy. "Maybe the future is now."

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