Doyle Rice, and Trevor Hughes

USA Today

While a Pineapple Express storm delivered much-needed rain and snow to California this week, the state is still struggling with persistent drought that's left reservoirs well below normal and farmers hoping things change -- soon.

A new study says the drought is the worst California has seen in 1,200 years, and this week's moisture may have only been "two drops" in the bucket, meteorologist Jan Null of Golden Gate Weather Services said.

Getting out of the drought will be a long, uphill battle, he added. Over the past three rainy seasons (2011-12, 2012-13, and 2013-14) in San Francisco, for example, Null said the city has been a whopping two feet short of its typical rainfall.

"The bottom line is we need to make up at least some of the deficit from the past three years," he said. "It's not enough to just pay off this year's credit card debt, you have to at least pay down some of the previous debt!"

"We have to be patient in measuring improvement….more on the scale of months, not weeks or events," said Mark Svoboda, a climatologist with the National Drought Mitigation Center. "This recent wet pattern needs to continue and sustain itself over the coming months in order to really begin eroding away at those 3-year deficits," he said.

Federal officials are concerned because California is a major producer of fruits, vegetables, tree nuts, and dairy, which means if farmers can't produce as much, food prices will rise.

There have been only tiny improvements in California's reservoirs in the past week, according to the California Department of Water Resources. For instance, Lake Oroville in northern California went from 42% of its historical average last week to 44% this week.

This week's U.S. Drought Monitor, out Thursday morning, showed no improvement in the drought in California: 99.7% of the state is still in some form of drought. However, the cutoff date for data in the Monitor is Tuesday, so the full impact of this week's rain and snow won't be seen until next week's Monitor. Pineapple Express storms are Pacific systems carrying moisture off the ocean that come from the direction of Hawaii.

Typically, about one-half of California's annual precipitation is expected to fall during the December-February season, the Drought Monitor noted. However, more than this is needed to offset the accumulated deficits.

"It's going to take a couple years of average or above-average rainfall so that we can not only fill our reservoirs, build our snowpack, but also recharge our groundwater basins," said Bill Croyle with the California Department of Water Resources. "The ground is so dry, and the groundwater basins in those higher elevations have no water in them."

Researchers this week said a study of tree-growth rings indicates the current drought is the worst in at least 1,200 years. They compared tree rings with known moisture amounts to reach their conclusion, which was published in the the journal Geophysical Research Letters.

"We were genuinely surprised at the result," Daniel Griffin, a NOAA Climate & Global Change Fellow, said in announcing the study. " This is California--drought happens. Time and again, the most common result in tree-ring studies is that drought episodes in the past were more extreme than those of more recent eras. This time, however, the result was different."

The current short-term drought appears to be worse than any previous span of consecutive years of drought without reprieve, concluded Griffin and co-author Kevin Anchukaitis, an assistant scientist at Woods Hole Oceanographic Institution.

Contributing: KXTV News 10 Sacramento.