California Drought: 'Rain Debt' is Now Equal to an Entire Year's Worth of Precipitation

California's drought is becoming a serious issue. Now, NASA has revealed that the state has accumulated a debt of about 20 inches of precipitation between 2012 and 2015, which is the average amount expected to fall in a single year.

In an average year in California, 20 to 50 percent of its precipitation comes from relatively few, but extreme events called atmospheric rivers that move from over the Pacific Ocean to the California coast.

"When they say that an atmospheric river makes landfall, it's almost like a hurricane, without the winds," said Andrey Savtchenko, one of the researchers, in a news release. "They cause extreme precipitation."

In order to get a better sense of California's drought, the researchers examined data from 17 years of satellite observations and 36 years of combined observations and model data. They found that the state as a whole can expect about 20 inches of precipitation each year with regional differences. However, the total amount can vary as much as 30 percent from year to year. Usually, precipitation varies enough from year to year that the total amount balances out.

Recently, though, California has been going through a drought. From 2012 to 2014, in fact, the state accumulated a deficit of almost 13 inches. Then from 2014 to 2015, this debt increased another seven inches to make 20 inches total.

"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," said Savtchenko. "But, even if the climate doesn't change, are our demands for fresh water sustainable?"

The findings reveal a bit more about the drought conditions in California and show just how severe the current drought has been. With that said, it seems as if the drought is breaking for now, which is good news for the state.

The findings are published in the Journal of Geophysical Research: Atmospheres.

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