San Joaquin Valley Water Supplies – Unavoidable Variability and Uncertainty.
We look at how major flows into and from the Valley vary and the uncertainty in such water balance estimates, with some policy and management implications.
Balanced water management in California must prepare to operate across diverse wet and dry year conditions.
Large outflow and water use changes, and long-term groundwater overdraft, are clearly seen, including recent droughts – where natural availability averaged 2.3 MAF/year less for 2007 to 2015 than its 30-year average.
Large Statistical Uncertainty in Major Inflows Estimates of individual inflows or outflows are more straightforward, but always include some error from measurement inaccuracy, modeling uncertainty, and hydrologic variability.
Average flow estimates, such as those for the San Joaquin Valley water balance, are the basis for many water policy, planning, management, and regulation decisions.
Planning around water balances often overlooks these uncertainties.
Three important implications from these unavoidable uncertainties and variability are: Given California’s natural hydrologic variability, and the inherent uncertainty of our models, water and groundwater plans need to be prepared for simple long-term water balances to be substantially wrong.
Source and sustainability planning should also account for uncertainty estimates and try to reduce them over time to improve the accuracy of their water budgets estimations.
Accounting Water for the San Joaquin Valley.