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California’s unprecedented dry spell has tested the limits of drought-tolerant ferns, which carpet the forest floor underneath the West Coast’s iconic redwoods, according to a new study by UC Santa Cruz scientists.

“We’ve never seen a drought of this magnitude,” said co-author Jarmila Pittermann, associate professor of ecology and evolutionary biology. “You’re used to seeing a green understory, but in the last four years without rain, they’re white or brown. They dried up.”

 What a difference a month of rain makes.

Two months ago, Folsom Lake stood at its lowest depth in history, and federal officials were engineering a special pumping system to ensure drinking water would keep flowing to Sacramento suburbs.

Following a month of persistent rain and snow in Northern California, lake levels are triple what they were in early December, and the reservoir contains more water than average for early February.

The Obama administration has begun an initiative aimed at making the United States more water-efficient, saying the country has the potential to reduce its total water use by a third.

Deputy Interior Secretary Mike Connor said some of the White House’s objectives include encouraging more recycling of wastewater and promoting investment in water treatment and desalination technologies.

The first month of 2016 was the wettest January in Sonoma County in six years and saw the most rainfall for the period since the start of the current drought, a hopeful sign as the North Coast and the rest of the state struggle to recover from four years of scarce precipitation.

The National Weather Service measured 10.01 inches of rain at its gauge at the Charles M. Schulz-Sonoma County Airport in Santa Rosa during the month of January. That’s more than the previous four January months combined, since the drought began in 2012.

On the edge of the Central Valley is the center of California’s water system: the Sacramento-San Joaquin River Delta, where the state’s two largest rivers meet.

A plan to restore the Delta by channeling water down south has long been a priority for Governor Jerry Brown’s administration. Despite its various names and strategies, the project has been riddled with controversy since Brown first assumed office in the late ’70s.