There's no end in sight for California's historic drought

California has now endured four years of brutal drought, arguably the worst in state history. Reservoirs have shriveled. Crops are wilting in the fields. Cattle herds are thinning out. Hydropower dams are generating less electricity.

California's snowpack was at just 6 percent of historical levels

And, rather than getting better, things actually seem to have taken a turn for the worse this winter.

Typically, the nearby Sierra Nevada mountains get a lot of snow at the beginning of the year that then melts throughout the spring. This system normally provides California with about one-third of its freshwater.

But this year was different. As of March 31, California's snowpack stood at just 6 percent of historical levels. Those are utterly shocking numbers — the previous record low for this time of year was 25 percent, reached last winter. And this is in a state that was already low on water:

Beautiful satellite shot of CA yesterday. Meager Sierra snowpack clearly visible #cawx pic.twitter.com/ENUVf1UUmt — NWS Sacramento (@NWSSacramento) March 26, 2015

Now, on the bright side, the state has gotten a fair bit of rain this winter, and its reservoirs have bounced back a bit. Lake Oroville, a key reservoir in the system that brings water from northern to southern California, is at 51 percent of capacity (it was at 49 percent a year ago). Still, the lack of snow means there will be little additional water coming in when it gets warmer this spring. It's a dire situation.

California's long-term water problems are serious — especially for farms

California has struggled through drought before. But the current dry spell stands out as unusually severe — and the state is facing a real water crunch.

One study in Geophysical Research Letters found that this is California's worst drought in 1,200 years, driven by a lack of rainfall and record heat. (There's a lot of debate over the extent to which global warming caused this current drought, but high temperatures do seem to be exacerbating matters.)

California's farms provide half the fruits and veggies grown in the United States

That's particularly a looming issue for California's agricultural sector, which is responsible for about half the fruits and vegetables grown in the United States, including the vast majority of almonds, broccoli, strawberries, and grapes. Agriculture uses about 80 percent of the state's developed water supply — four times as much as all the towns and cities put together.* And it's now under strain.

This year, for the second year in a row, many of California's farmers won't receive any water from the Central Valley Project, which allocates water from the state's reservoirs. Last year, more than 400,000 acres of farmland in the Central Valley were left fallow after this happened.

Without reservoir water, many of California's farmers have instead been sucking out freshwater from beneath the ground to irrigate crops like almonds. (After all, almond farmers can't just choose not to plant in dry spells — if they don't water their trees, the trees die.) According to one UC Davis study last year, California's farmers have been replacing about three-fourths of lost rainfall with groundwater.

For now, there's nothing preventing this from happening: While some other states have laws regulating how much water can be pulled out from underground aquifers, California lets pretty much anyone draw as much out as they want, as long as it's for a useful purpose. The state recently enacted new regulations on this pumping, but they won't take effect until 2020.

As a result, satellite surveys have shown, California's groundwater has been vanishing at a shocking rate:

That groundwater pumping has helped farmers avoid immediate disaster. But there's a long-term dilemma here. These underground aquifers aren't easily refilled, since they were built up over centuries. That means farmers are losing a crucial buffer against future droughts.

This is particularly alarming because California has faced decades-long "mega-droughts" in the very distant past, and some experts have wondered whether the state might now be in the midst of another. (Scientists also think mega-droughts will be more likely in the future as global warming worsens.) It all points to the need for California to drastically rethink its water habits.

"California has no contingency plan for a persistent drought like this one (let alone a 20-plus-year mega-drought), except, apparently, staying in emergency mode and praying for rain," wrote NASA water scientist and University of California-Irvine professor Jay Famiglietti in a widely circulated op-ed in March. He called for "immediate mandatory water rationing."

California has been slow to adopt rationing — until now

Up until now, California politicians have been reluctant to enact mandatory statewide water restrictions — opting for other, more gradual steps and local conservation measures first.

New rules on groundwater pumping won't take effect for six years

Back in 2014, California voters approved a $7.5 billion water bond to fund new water recycling, desalination, and drought-preparedness projects, but those will take time to get underway. The state also tried to provide incentives to boost water efficiency and conservation, although those measures have been falling short.

Last year, the state legislature also approved new restrictions on groundwater pumping from agriculture, but those won't take effect for another five years and will then be phased in gradually between 2020 and 2040. Some experts have lamented that these restrictions on agriculture are much too flimsy — and weaker than those in other Western states.

Then, last month, as the low snowpack became clear, California started to take further action. On March 17, the state directed urban agencies to set new restrictions on how frequently residents could water their yards. On March 19, Jerry Brown announced $1 billion in new spending for short-term relief — including emergency drinking water — as well as accelerating some of those water-bond projects for recycling and desalination.

Now Brown is announcing the first-ever mandatory restrictions, mostly for urban water usage. The new measures include:

The State Water Resources Control Board will implement mandatory water reductions in cities and towns across California to reduce water usage by 25 percent. This savings amounts to approximately 1.5 million acre-feet of water over the next nine months, or nearly as much as is currently in Lake Oroville.

Replace 50 million square feet of lawns throughout the state with drought tolerant landscaping in partnership with local governments;

Direct the creation of a temporary, statewide consumer rebate program to replace old appliances with more water and energy efficient models;

Require campuses, golf courses, cemeteries and other large landscapes to make significant cuts in water use; and

Prohibit new homes and developments from irrigating with potable water unless water-efficient drip irrigation systems are used, and ban watering of ornamental grass on public street medians.

Calls on local water agencies to adjust their rate structures to implement conservation pricing, recognized as an effective way to realize water reductions and discourage water waste.

Of course, these rationing measures don't apply to California agricultural users, who, again, uses about four times as much water as urban users. (That's even though farming accounts for just 2.1 percent of the state's GDP.) So it's quite possible that the state may have to revisit this issue yet again if the drought continues to persist.

"Today we are standing on dry grass where there should be five feet of snow. This historic drought demands unprecedented action," Brown said in a statement. "As Californians, we must pull together and save water in every way possible."

* Footnote

To be precise, agriculture in California uses about 80 percent of the state's developed water supply but only 40 percent of the state's total water. How does that work?

If you're looking at total freshwater use in California, roughly 50 percent is actually set aside for environmental purposes — i.e., it's allowed to stay in streams or wetlands to maintain ecosystems. Another 40 percent or so goes to agriculture, and the remaining 10 percent goes to cities and towns. (These precise numbers fluctuate between wet years and dry years.)

So, of the water that's stored behind dams and in reservoirs and is intended for economic purposes — what's known as the "developed water supply" — about 80 percent goes to farms and 20 percent goes to cities and towns. But that's why you often hear different numbers bandied about.

Further reading

— Could water markets help solve the West's water crisis?

— Also note that one recent NASA study projected that "mega-droughts" lasting more than three decades could become more likely this century if global greenhouse-gas emissions kept rising and the West continued to heat up.