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El Nino and the California drought — what does ESP say next year will bring ?

June 27, 2014

We’ve all heard the news – El Nino is coming! We’ll be saved! But what does that really mean in terms of the California drought? Bottom line is we stand about an 8% chance of recovering from the drought of the past two water years. And by recovery we’re just talking about getting back to a normal precipitation value.

CNAP researcher Mike Dettinger provides us with an excellent explanation of what we might expect — find the full story at:


ESP (Extended Streamflow Prediction) is a strategy of looking at the performance of the past to make estimates of the future. While El Nino often means wet conditions for California it is not always the case so looking at the range of possibilities Mike examines the drought precipitation “hole” we are in (and it’s a big one) — and the chances we might get out of the hole based on our experiences with El Ninos since 1932.



Mike looks at climate division precipitation data since the approximate start of the current drought (water year 2012/13 ended dry). Then he looks at precipitation since the beginning of our current water year (October 2013). These are the black squares on the graph below. Then he looks at how much precipitation we might get for the rest of the water year (through September 2014) if we had an El Nino (red), a La Nina (blue) or neutral (green) conditions. Any way you dice it we are still going to end up about 10 inches short of where we should be as a state (first straight thick line at about 22 inches). Now if we use the ESP strategy and look forward through the coming water year (2014/2015) and looking only at El Nino (presumably wet) years, the graph shows there is a 21% chance we won’t even get to fill in the hold from water year 2013/2014. And we see the 8% chance that we might fill in the hole and get back to normal.






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