Drought Information Banner

Water Unavailability Methodology for the Delta Watershed

Due to critically dry conditions in the Sacramento-San Joaquin Delta (Delta) watershed resulting in insufficient water supplies to meet all water demands, water quality objectives, and flow requirements, the State Water Board developed the Water Unavailability Methodology for the Delta Watershed (Water Unavailability Methodology for short) in May 2021. The Water Unavailability Methodology identifies when supply and demand data indicate that water is unavailable for diversion by water right holders at their priorities of right.

The Water Unavailability Methodology is being used to support the issuance of curtailment orders to water right holders and claimants in the Delta watershed pursuant to an emergency regulation when warranted by current conditions. To see which water rights and claims are currently curtailed, see the Delta Watershed Curtailment Status List.

The Water Unavailability Methodology has been refined in response to public comments and may continue to be updated to reflect the best available information. The Water Unavailability Methodology improves upon the approach used during the drought years of 2014 and 2015. Additional improvements will likely be possible in the future with better data and improved tools.

  Please see our Frequently Asked Questions for more information regarding water unavailability in the Delta watershed and the related Water Unavailability Methodology.

Announcements

  • April 3, 2023 – Curtailment and Reporting Orders Rescinded for the Sacramento-San Joaquin Delta Watershed. For more information, please visit the Delta Watershed Curtailment Status List section on the Delta Drought webpage.
  • March 21, 2023 - Written Public Comment Deadline Extended to 5:00 PM on April 14, 2023, for Comments on Potential Legal Delta and Return Flow Water Supply Refinements to the Water Unavailability Methodology for the Delta Watershed
  • March 15, 2023 – Resources Available Following Staff Workshop on Potential Legal Delta and Return Flow Water Supply Refinements to the Water Unavailability Methodology for the Delta Watershed (see Previous Events section below)
  • January 19, 2023 – Update to Resources Related to the Water Unavailability Methodology for the Delta Watershed Now Available (see Methodology Resources below)
  • November 15, 2022 – Resources Available Following Staff Workshop on Proposed Refined Watershed Analysis and Friant Priority Date Adjustments in the Water Unavailability Methodology for the Delta Watershed (see Previous Events and Actions section below)

Methodology Resources

Resource (Date Last Updated) Resource Description Prior Versions

Summary Report
(01/19/2023)

Summary Report Redline Comparison
(01/19/2023 to 06/27/2022)

The summary report outlines the methods used to develop the tool and describes the data sources, assumptions, and the bases for the assumptions used to develop the methodology.

The redline comparison shows changes between the prior and current versions of the summary report.

06/27/2022
04/19/2022
11/15/2021
09/27/2021
08/20/2021
07/23/2021
06/15/2021
05/12/2021

Technical Appendix A: Methodology Spreadsheet Description
(01/19/2023)

Technical Appendix A Redline Comparison
(01/19/2023 to 06/27/2022)

The appendix describes the data sources used to develop the methodology, calculation steps used in the analysis, and outputs used to create the visualizations. It is presented as a data dictionary for the Water Unavailability Methodology Spreadsheet (see below).

The redline comparison shows changes between the prior and current versions of appendix A.

06/27/2022
04/19/2022
02/18/2022
11/15/2021
09/27/2021
08/20/2021
07/23/2021
06/15/2021
05/12/2021
Technical Appendix B: Demand Data Development Process
(04/19/2022)
The appendix describes how user-reported data from 2018 and 2019 was collected and processed for the water demand dataset used in the methodology. 11/15/2021
09/27/2021
07/23/2021
06/15/2021
05/12/2021
Appendix C: Summary of Public Comments
(11/15/2021)
The appendix summarizes the substantive technical, factual, or legal comments that were received prior to the release of the July 23, 2021 version of the summary report. 07/23/2021
06/15/2021

Technical Appendix D: Assessment of Water Unavailability Issues Within the Legal Delta
01/19/2023

Technical Appendix D Redline Comparison
(01/19/2023 to 06/27/2022)

The appendix provides additional background information used to evaluate water unavailability in the Legal Delta portion of the Delta watershed.

The redline comparison shows changes between the prior and current versions of appendix D.

06/27/2022
09/27/2021
08/20/2021

Redline Comparison
09/27/2021 to 6/27/2022
Water Unavailability Methodology Spreadsheet
(01/31/2023)*

The spreadsheet contains the supply and demand datasets and analyses used to implement the methodology and create the visualizations.

*The Water Unavailability Methodology is run frequently in order to determine curtailments based on the most up-to-date water supply forecasts. To obtain a copy of the spreadsheet supporting current curtailments or for a specific date, please send an email to Bay-Delta@waterboards.ca.gov with ‘Request for Water Unavailability Methodology Spreadsheet’ in the subject line.

01/19/2023
06/27/2022
04/19/2022
02/18/2022
11/23/2021
11/18/2021
11/15/2021
09/27/2021
08/20/2021
07/23/2021
06/16/2021
05/12/2021

Public Comments

Since the Water Unavailability Methodology was released in May 2021, State Water Board staff have held several workshops to receive public input. Staff have also received and reviewed numerous written public comments. Comments received have informed subsequent updates to the methodology.

  To request a copy of written public comments on the Water Unavailability Methodology for the Delta Watershed, please send an email to Bay-Delta@waterboards.ca.gov.

Previous Events

  How to Report an Unauthorized Diversion

The State Water Board relies on the public to help identify unauthorized diversions, diversions by junior water right holders that impact senior water right holders, diversions in violation of permit and license conditions, diversions that constitute the waste or unreasonable use of water, and diversions that cause adverse impacts to public trust resources, such as fish and wildlife.

Report an Environmental Concern logo

  If you have information that an unauthorized diversion may be occurring, you can submit a complaint through the CalEPA Environmental Complaint website.

  Please visit the Complaints Program webpage for more information on water rights enforcement complaints.

  Stay informed

Email Subscription Topic

Subscribe to the Delta Drought email topic to receive notifications and the latest updates.

Contact Us

If you have specific questions or concerns related to the Water Unavailability Methodology for the Delta Watershed you can reach us at:

For inquiries on other drought-related tools please contact: