Following the water in the Sacramento-San Joaquin Delta Watershed: Where the water goes, controversy follows

The Sacramento-San Joaquin Delta has been the focus of water woes and wars in California for over 100 years. The conflict involves upstream water uses, in-Delta water uses, Delta water exports, Delta outflow needed to repel seawater intrusion into the Delta, and freshwater flows needed to provide adequate habitat for aquatic species. This seminar briefly reviews changes in Delta regulations over time, and changes in the estimates of Delta outflow needed to keep the Delta fresh. It then reviews the results of Public Policy Institute of California studies that examined watershed unimpaired runoff, stored water, imported and exported water, upstream and in-Delta uses, and Delta outflow from 1980 to 2021 on daily to annual time scales. Delta outflow was classified according to flows needed for system requirements (to keep the Delta fresh enough for human uses of Delta water), Delta ecosystem requirements, and uncaptured flow. The change in the amounts of water used in these categories largely follows the changing climate and evolving regulations. The analysis dispels some myths about the quantities of water used in the various categories and their trends. It also demonstrates the State’s high reliance on runoff from snowmelt which has seriously declined over the last 20 years as temperatures rose, and it shows that the system essentially “broke” in 2021 when total upstream and in-Delta uses exceeded runoff, leaving only stored water to meet Delta outflow requirements and Delta water exports. In contrast, the analysis shows that large amounts of water could have been exported in wet years even with stringent ecosystem protection requirements in place, but those exports were foregone due to lack of available storage.

Speaker: Greg Gartrell, Public Policy Institute of California