The State Water Project Delivery Reliability Report may have created systemic drought vulnerability

On June 7, 2022, Adel Hagekhalil, general manager of the Metropolitan Water District of Southern California, issued the following statement:

We are in an unprecedented situation, where our water supplies from the State Water Project are so limited by drought and climate change that they do not meet demands. Southern Californians must decrease their water use. I know we can do it.

“Our board’s action in late April to mandate dramatic cuts in water use in one-third of Southern California… generated widespread public attention to the drought’s severity. That new public understanding of our alarming water supply crisis… must prompt strong action, or we won’t have enough water to get us through the year.

MWD’s water supply crisis can be traced to the Department of Water Resources’ State Water Project Delivery Capability Reports (DCRs.)  In the Draft 2021 Delivery Capability Report, the Department of Water Resources characterized Water Year 2021 (WY 2021) runoff as “atypical” and stated that DWR would consider climate change driven shifts in hydrologic conditions in future DCRs, if their analysis determined that hydrologic conditions had shifted outside the long-term historical distribution.

Potential Climate Change Driven Shifts in Hydrologic Conditions

DWR constantly reviews and analyzes hydrologic conditions in California and has been monitoring potential shifts in hydrology. The recent hydrologic conditions have been notable for warmer average temperatures, drier average annual precipitation, and a decreasing Sierra Nevada snowpack which impacts the timing and magnitude of snowmelt runoff volumes. WY 2021 was also atypical in that it had much lower snowpack runoff efficiency than any previously documented year. DWR has multiple efforts underway to evaluate and compare long-term and recent hydrologic characteristics. If it is determined that hydrologic conditions have shifted outside of the long-term historical distribution of conditions, upcoming DCRs will include adjustments to account for these changes.
(p. 21.)

These were the projections for State Water Project Table A deliveries in a 2,4-, and 6-year drought in the 2019 and 2021 Delivery Capability Reports. Metropolitan Water District and every other water agency in California that gets State Water Project water has relied on these estimates for their drought contingency planning.

The estimates of average deliveries of 33% of Table A contract amounts in a 2 year drought, and 22% in a 4 year drought, are much higher than the actual 2022 allocations of 5%. Because of reliance on the DCR estimates, MWD was unprepared for a 5% allocation in 2022.

In a previous blog post, “Dear DWR, Stationarity is dead,” we noted that in 2009 DWR’s own water resource engineers quoted an influential paper on water management under climate change by Milly et. al. (2008.) Milly et. al. stated that “’Stationarity is dead’ and that ‘finding a suitable successor is crucial for human adaptation to a changing climate.’”

The Department of Water Resources did not even publish the climate change scenario results with the draft report, stating:

The 2021 Final Main Report (released at the end of March 2022) may include further information on climate change. Previously, the climate change scenario results were only discussed and presented in the Technical Addendum which is not published during the draft phase of the Delivery Capability Report (DCR.)

The Department of Water Resources did not release the 2021 Final Main Report in March. DWR needs to notify State Water Project Contractors of the potential vulnerabilities in the Delivery Capability Report estimates, and work on rapidly developing alternative projections that incorporate deep uncertainty due to accelerating climate change impacts.

This post was updated on June 18, 2022.

Further reading

Deirdre Des Jardins. 2022. Dear DWR, Stationarity is dead. California Water Research blog, February 17, 2022.

Department of Water Resources. 2021. The Draft State Water Project 2021 Delivery Capability Report.

Department of Water Resources. 2019. Delivery Capability Report and Studies 2019.

Metropolitan Water District of Southern California. 2022. Metropolitan General Manager Issues Statement on Latest Statewide Conservation Numbers. Press release. June 7, 2022

Milly, P.C., Betancourt, J., Falkenmark, Hirsch, R., Kundzewicz, Z., Lettenmaier, D., D., Stouffer, R. 2008. Stationarity Is Dead: Whither Water Management? Science 319(5863): 573-574. doi:10.1126/science.1151915

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