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DWR Increases SWP Allocation to 30% after Storms

On February 24th, the Department of Water Resources increased the estimated State Water Project Allocation to 30%, although it warned that extended dry weather could force a reduced allocation.  This is the third announcement concerning the department’s estimated Table A allocation, starting at 10% last December and increased to 15% in late January.


DWR’s current announcement is in accord with the Journal of Water’s predictions for the 2016 Final Allocation.  Updating JOW’s forecast for the 2016 Final Table A Allocation for actual precipitation as measured by the Northern Sierra 8 Station Index through January, the expected final allocation is 29% (see Probability Distribution Chart).  There is about a 50% chance that the Final Table A Allocation will be less than 30%.

Probability Distribution (02-2016)_WEB

There are two wild cards to keep one’s eye on as we wait for the Department of Water Resources’ determination of the Final SWP Allocation for 2016.

First, there is the fickleness of Mother Nature. What will precipitation be in the coming months?  January storms portend a continuing favorable factor towards increased SWP allocations.  Based on the historical relation between the cumulative precipitation for October-April precipitation and the cumulative precipitation for October-January as measured by the Northern Sierra 8 Station Index, the expected precipitation for October-April now stands at 53.1 inches, or 114 percent of the historical average.  The predicted 29% allocation in the face of above normal precipitation reflects the low storage in Oroville at the beginning of the water year and the declining trend in SWP Allocations reflecting environmental restrictions.  (For further discussion of the factors driving SWP allocations, see California DWR Announces Initial SWP Allocation, JOW December 2015).

Second, there are man-made actions. What will be the impact of environmental constraints on project operations?  Does the model’s trend decline of 3 percentage points per year for the Final SWP Allocation capture reduced allocations from regulatory constraints?

In the end, there is much uncertainty surrounding the outcome. JOW will update the predictions monthly for actual precipitation through April.


Written by Rodney T. Smith, Ph.D.