NASA scientists say it will take 11 trillion gallons of water to replenish two of California's drought-starved river basins and help reverse the state's drought.

That figure comes courtesy of measurements taken from NASA GRACE satellites, recently released by a team of scientists, which discovered an 11 trillion gallon shortage of water in the Sacramento and San Joaquin river basins.

Combined, the two basins account for about 51 percent of California's water supply, according to the California State Water Resources Control Board. Additionally, the satellite analysis found that the two basins lost four trillion gallons of water a year since 2011, most of which came from groundwater sources.

The measurements mark the first time scientists have ever been able to determine exactly how much water is needed to replenish an area stricken by drought.

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"Spaceborne and airborne measurements of Earth's changing shape, surface height and gravity field now allow us to measure and analyze key features of droughts better than ever before, including determining precisely when they begin and end and what their magnitude is at any moment in time," said Jay Famiglietti of NASA's Jet Propulsion Laboratory.

"That's an incredible advance and something that would be impossible using only ground-based observations."

Another key component to ending the drought will come from snowpack, particularly in the Sierra Nevada. In the spring, snow accumulated throughout the winter in the upper elevations melts as temperatures increase.

That Sierra Nevada meltwater trickles down throughout the hydrological system, providing 60 percent of the water in California's reservoirs, the lifeblood of the state's more than 38 million people, particularly during the dry season, which last for seven months out of the year.

Unfortunately, a study from NASA's Airborne Snow Observatory showed that the snowpack in the Sierra Nevada range experienced a similar fate to the Sacramento and San Joaquin river basins in 2014. As NASA notes, the new analysis found that total snowpack in the Sierra Nevada was actually half that of previous estimates in early 2014.

"The 2014 snowpack was one of the three lowest on record and the worst since 1977, when California's population was half what it is now," said Tom Painter, NASA's Airborne Snow Observatory's principal investigator.

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Unfortunately, while a series of storms have dumped substantial rain and snow on California, the state still needs a substantial amount of precipitation over a long period of time to reverse a drought three years in the making.

"It takes years to get into a drought of this severity, and it will likely take many more big storms, and years, to crawl out of it," said NASA's Famiglietti.

MORE ON WEATHER.COM: Before and After California's Drought

The Green Bridge passes over full water levels at a section of Lake Oroville near the Bidwell Marina on July 20, 2011, in Oroville, California. (Paul Hames/California Department of Water Resources/Getty Images)