An image shows the areas where the state's rain debt has been most dramatic, the larger the precipitation deficit, the redder the map. Photo by NASA/Goddard Scientific Visualization Studio

LOS ANGELES, July 30 (UPI) -- It would take a whole year's worth of precipitation to replenish the drought-ridden soils of California and erase the state's so-called "rain debt."

That's the takeaway from a new study by researchers at NASA's Goddard Space Flight Center. The scientists used decades of satellite data and ground-based precipitation measurements to analyze average rain and snow totals.


The data was used to calculate how far recent precipitation totals have fallen short of expected averages.

Averages aren't necessarily the norm, but the middle point between fluctuations. In non-drought periods, wet and dry years balance each other out. But according to the new study -- published in the Journal of Geophysical Research -- California has experienced a string of dry years between 2012 and 2014, building up a rain deficit of 13 inches.

Another seven inches have been added in recent months, bringing the total debt to 20. That's the equivalent of an average year's precipitation in the Golden State.

The team of researchers, led by Andrey Savtchenko, say the state's rain debt and ongoing drought is mostly the result of a stationary high-pressure system off the coast that's continually blocked the formation of what scientists call "atmospheric rivers."

Atmospheric rivers are narrow bands of water vapor that travel between differing bodies of moving air, sometime propelled by and along with jet streams. They exist all over the world and generally travel west to east. When they arrive on the coast of California from the Pacific, these condense bands of water-rich air are pushed up by the mountains, squeezing the water out in intense rainfall events.

California, the new research suggests, relies on these rivers to supply anywhere from a quarter to a half of their average precipitation total.

"When they say that an atmospheric river makes landfall, it's almost like a hurricane, without the winds. They cause extreme precipitation," Savtchenko explained in a press release.

Some forecasters have suggested the strengthening El Nino system off the Southern California coast could encourage a more active rainy season during the fall and winter, alleviating the state's drought. But while the system is more likely to encourage rain than not, Savtchenko says El Nino patterns are a small factor in governing California's long term precipitation trends.

The new research suggests dramatic precipitation variability and long droughts are simply a fact of life in California. Some suggest it will only get worse as the planet warms. It's a conundrum that's a reality for more and more people as the state's population continues to grow.

"Drought has happened here before. It will happen again, and some research groups have presented evidence it will happen more frequently as the planet warms," Savtchenko said. "But, even if the climate doesn't change, are our demands for fresh water sustainable?"