How deep of a precipitation hole is California in?
A BIG one.
Wait, you want more detail than that? One sentence won’t suffice? I suppose that is reasonable request.
In January, after a series of rain events the previous month in California, I wrote an article using analysis from my Climate Prediction Center colleague Rich Tinker that described how much rain/snow was needed by the end of the California water year (the end of September) to get California out of its precipitation hole.
The answer was a lot of precipitation. It would have taken near record amounts of rain across the agriculture-dominated central California – the San Joaquin Valley – to bring the most recent four year period out of the driest 20 percent of years on record. Flash forward to September and those rains did not happen last year. In fact, California remains extremely dry.
The most recent US Drought Monitor, released September 8, has 46% of the state under the most extreme drought category (D4-Exceptional Drought). Over 97% of the state is experiencing some degree of drought. Only areas in far southeastern California have received enough rain to simply be abnormally dry and not under drought.
So what will it take for the upcoming water year to put a big dent into California’s precipitation deficits?
Again the answer is a lot of rain. As of the end of August, California is running 5-year precipitation deficits (starting in October 2011) of 8 inches in the dry southeast to almost 50 inches along the north coast. In California, four year rainfall amounts (2011-2014) have been between 54-75% of normal during that time frame. To put the deficits into another perspective, every region in California is missing at least a year’s worth of precipitation. In fact, the south coast of California Is missing almost two year’s worth of rain (1.82 years to be exact). This deficit isn’t so much a hole as a giant chasm.
One measure used by the U.S. Drought Monitor team to declare drought is whether precipitation totals are in the bottom 20 percent of the record. For five-year precipitation totals (October 2011 – September 2016) to get out of the bottom 20% of records dating back to 1928, precipitation totals from October 2015 through September 2016 must exceed 135-160% of normal in northern California, 160% of normal in the dry southeast to 198% of normal in the San Joaquin Valley. This is a ton of rain/snow.
Press link for more: Tom D Liberto | climate.gov