Report 2022-106 Recommendation 5 Responses

Report 2022-106: Department of Water Resources: Its Forecasts Do Not Adequately Account for Climate Change and Its Reasons for Some Reservoir Releases Are Unclear (Release Date: May 2023)

Recommendation #5 To: Water Resources, Department of

To ensure that its operation of the State Water Project reflects the possibility of more extreme climate conditions, DWR should, by May 2024, evaluate the data and information that it relies upon in its monthly and annual planning for its Lake Oroville reservoir operations, including the volumes of water that it will need to store to achieve its objectives. It should update the data and information as needed.

1-Year Agency Response

The Water Supply Guidelines Project Operations and Maintenance Directive (POMD) establishes triggers to review and update the parameters (for example, Lake Oroville reservoir operations and hydrology) used in assessing available State Water Project water supply in planning studies. Examples of changing conditions that could trigger a re-evaluation of parameters include, but are not limited to, physical capacities and new regulations and operating agreements.

Data used in developing operational and planning studies have been evaluated and updated consistent with industry best practices. This includes hydrologic exceedances based on a 30-year period and incorporates the most recent hydrologic extremes. Salinity to outflow relationships were updated based on recent data and reflect current sea levels and these relationships have been implemented in the planning studies using an updated methodology.

California State Auditor's Assessment of 1-Year Status: Fully Implemented

6-Month Agency Response

DWR will implement a periodic review process of the information it relies on for Oroville reservoir operations planning. DWR is on track to implement Recommendation No. 5 by May 2024.

California State Auditor's Assessment of 6-Month Status: Pending

60-Day Agency Response

A key input of the SWP planning studies is the DWR's Bulletin 120 hydrology forecast that provides a range of potential water runoff volumes for the given water year. As DWR improves the Bulletin 120, it will automatically be incorporated into the SWP planning studies. DWR will continue to evaluate data needs for the SWP planning studies and update our data accordingly.

California State Auditor's Assessment of 60-Day Status: Pending

As we describe in the text of the report, DWR used various data and information beyond the water supply forecasts in the Bulletin 120 when developing its allocation analysis to inform its Lake Oroville reservoir releases and storage. We found that the data and information DWR used in those analysis was largely historical and possibly outdated. We look forward to reviewing DWR's future updates regarding its evaluation of those data and the need to update it.

All Recommendations in 2022-106

Agency responses received are posted verbatim.