Guest commentary by Robert Shibatani:
Every year at this time as the new water year unfolds, predictions and warnings about California’s upcoming water supplies begin emerging each one trying to project the likely status of water availability in the upcoming months. To facilitate such predictions a rich bevy of resource data are available. These databases are shared among the various federal, State, and local agencies as well as research and academic institutions, all of which collectively help to refine and tailor these projections. Despite their coverage and seeming quality, we should not lose sight of the fact that these forecasts still remain only best guesses. Well informed guesses to be sure but guesses all the same.
If we step back and ask ourselves what is it that we are actually trying to predict? Several answers become apparent; a real-time State water balance, deliverable raw water; or finished, treated water. Alternatively, are we more interested in simply assigning a water year classification (e.g., critically dry, below normal, drought, wet, etc.) in deference to how our regulations are controlled? I believe that we are seeking a combination of all four. Ultimately, we want (and need) to know how much potential water will be available for beneficial use by the State’s water users.
To get that answer, California water planers are fortunate in that there is no shortage of readily available data. These are wide-ranging and include mainstem basin river indices, sub-basin station indices (e.g., 8-station, 5-station, Tulare Precipitation Index), groundwater data (e.g., CASGEM), reservoir storage summaries, river temperatures, snowpack SWE (e.g., California Cooperative Snow Surveys), etc. These data are dutifully collected and enjoy good spatial and temporal acuity, enough to provide regulators and water managers with a depiction of current hydrologic conditions and forecasted changes as determined by the California Nevada River Forecast Center and National Weather Service.
The California-Nevada drought outlook is based largely on the U.S. Drought Monitor, relying on precipitation and temperature (e.g., Palmer Drought Severity Index, the Standardized Precipitation Index, and other climatological inputs); the Keech-Byram Drought Index for fire, satellite-based assessments of vegetation health, crop bulletins, various indicators of soil moisture, El Niño status, hydrologic data such as the Surface Water Supply Index, and not to be overlooked, the expertise of many specialists like the State Climatologist or the Lead Forecaster for the NWS.
Since informed projections are best made when ALL factors are considered, various man-made factors must also be considered. These, after all, have as much an effect on whether deliverable raw water becomes available or not. Such man-made factors typically include water infrastructure, regulations, and operations. Here is where operational facets such as reservoir capacity, inflows and releases, federal/State exports, pumping and releases between the DMC and California Aqueduct, Delta outflow indices, water accounting, etc. would come into play. The State’s water resource status at any given time depends on how operations, regulations, and water accounting is being managed.
If having access to, and consideration of ALL influential factors is essential in making legitimate claims of water status, we must ask ourselves whether we do this? I conclude that despite having appropriate information available, the data are not consistently used in the decision process thus, water shortage or drought declarations are being made on incomplete information.
We do not, for example, provide a suite of supply enhancement scenarios based on operational adjustments. We do not say, “Precipitation to date is currently generating X reservoir inflow, however, despite existing flood control requirements and the obligation to spill, we will be encroaching into the flood pool by Y amount based on our assessment of water storage need and low precipitation forecasts...” Going further, we do not admit, “…without refill based on historic averages, continued depletion will result in water surface levels moving into the conservation pool zone thus likely resulting in a drought declaration by the end of April…”. More importantly, we do not offer any potential alternatives. We don’t propose for example, “… if we vary from the rule curve requirement and encroach by X amount, the percent likelihood of avoiding a 25% curtailment to all north of Delta M&I contractors would increase by Y…”. In short, we do not offer the public any “if-then” options. As a result, the public has no idea as to how flexible our operational choices really are.
Do we have flexibility in our various flood control rule curves? Of course, we do, particularly since almost all of the existing rule curves are outdated and few, if any have been revised to take into account a shifting winter/spring hydrologic regime due to a warming climate. Reservoir operators, if they chose, could operate around existing rule curves and potentially avoid the loss of significant quantities of water. In fact, to prove this point, we documented “spills” of over 600,000 AF from Folsom Reservoir during a recent January through May period only to have American River deliveries cutback later that same summer. Clearly, this was not a good example of effective reservoir management. But it happens year after year.
Coming back full circle, are our water projections reliable? I think most would agree that they are dependable, but the story does not end there. The public should know that, but for a few operational adjustments, the water status in any given year could be very different if reservoir/water operators were allowed to pursue other options after considering all risks. After all, despite what many think, droughts are not all about Mother Nature, there’s much more to the story…
Please note: The views in this commentary are those of the author’s and should not be attributed to Maven’s Notebook.
About the Author
Robert Shibatani, a physical hydrologist with over 35-years combined academic, legal, consulting and water advisory counsel, is an international expert witness on reservoir-operations and flood damage in the EU, UK, Australia and U.S., specifically as they pertain to major hurricanes. He is the Managing Partner for The SHIBATANI GROUP International and resides in Sacramento, California. robert@theshibatanigroup.com
