March Rains Increases Hydrowonk’s Prediction of Final SWP Allocation to 23%

Mother Nature’s generosity to California extended into March where precipitation was about average (which in California seems like a deluge these days). This March precipitation was greater than used in Hydrowonk’s predictions. So, Hydrowonk’s updated prediction for the expected Final SWP Allocation: 23%

Hydrowonk’s predictions are based on a study of the historic record of final State Water Project Allocations. The model relates final SWP Allocations to the amount of water in storage at Oroville at the beginning of the water year and precipitation as measured by the Northern Sierra 8-Station Index from October through April.

Despite Mother Nature’s bounty in March, cumulative precipitation remains significantly below average (now stands at 51% of average). Therefore, the predicted final SWP Allocation remains only slightly above the historic low of 20% reached in 1991.

There is considerable uncertainty surrounding Hydrowonk’s prediction. As shown by the probability distribution of predicted final SWP Allocations, the expected 23% allocation is the most likely number. The current zero allocation has only a 5% probability. There is a 25% probability that the final SWP Allocation will be less than 16%. There is a less than 25% probability that the final Allocation will exceed 30% and only a 10% chance that the final SWP Allocation will exceed 40%.

Mother Nature tossed California another bone in March. While helpful, the situation remains at the historic lows. The federal and state officials plan to announce soon new releases of water in response to the recent rains. Expect for announcement of significant releases of water. Whether project allocations move off zero depends on the environmental constraints that themselves got more complicated with the recent appellate court decision on the 2008 biological opinion by the U.S. Fish and Wildlife Service.

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