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%

Monthly Precip

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.

Cumulative Precip

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%.

Probability Distribution Mar Prediction

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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About Rodney T. Smith

Rodney T. Smith, Ph.D., President of Stratecon Inc.—an economics and strategic planning consulting firm—advises public and private sector water users on the acquisition, sale and leasing of water rights and water supplies in the western U.S. He is routinely involved in economic valuation of water rights, water investments, and negotiation of water acquisition and transportation agreements and has served as an expert witness in the economic valuation of groundwater resources, disputes over the economic interpretation of water contracts, economics of water conservation and water use practices, and the socio-economic impacts of land fallowing. For more information, see

3 thoughts on “March Rains Increases Hydrowonk’s Prediction of Final SWP Allocation to 23%

  1. Greg Gartrell

    No, most of the undelivered “carryover” was not in storage, some is, but not all, DWR allocated based on 90% forecast which includes unstored flows that did not materialize in a 99.8% year. So they owe from this year’s precip and storage for last year’s allocation. DWR’s forecast at 90% as of the end of March shows about 700 taf in deliveries, about 100 taf is already gone Jan-March, but it is not clear how much of that is for last year.

  2. Greg Gartrell

    Did you take into account that the SWP shorted the State Water Contractors more than 400 TAF last year (allocated 1.4 MAF and only delivered 1 MAF because they counted on unstored flows that never materialized)? Better subtract that from your predicted 23%.

    1. Rodney T. Smith Post author

      Thanks for the comment. Are you saying that the 0.4 MAF was not delivered, even though it was allocated and ordered? Did that mean that storage in Oroville was increased by 0.4 MAF? Is DWR administering that as turnback water? With 400,000 AF of less “available” water for storage in Oroville at the beginning of the year, my model would predict a lower SWP allocation (14%).


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