Winter wet–dry weather patterns driving atmospheric rivers and Santa Ana winds provide evidence for increasing wildfire hazard in California

Climate Dynamics (Springer) | August 12th, 2022

Floods caused by atmospheric rivers and wildfires fanned by Santa Ana winds are common occurrences in California with devastating societal impacts. In this work

Floods caused by atmospheric rivers and wildfires fanned by Santa Ana winds are common occurrences in California with devastating societal impacts. In this work, we show that winter weather variability in California, including the occurrence of extreme and impactful events, is linked to four atmospheric circulation regimes over the North Pacific Ocean previously named and identified as the “NP4 modes”. These modes come in and out of phase with each other during the season, result- ing in distinct weather patterns that recur throughout the historical record. Some phase combinations favor atmospheric river landfalls and extreme daily or multi-day precipitation, while other phase combinations favor anomalously hot weather and drying Santa Ana wind conditions over Southern California. This historical perspective of atmospheric circulation and impacts over 70 years reveals that weather patterns are changing in a way that enhances wildfire hazard in California, while the frequency of weather patterns linked to historical floods is not diminishing. These changes highlight the rising hazards of cascading weather extremes in California’s present and future.

Workshop report—Earthquakes and High Water as Levee Hazards in the Delta

Delta Stewardship Council (Delta Council) | September 30th, 2016

Earthquakes and high water as hazards to Delta levees were reviewed in a seven-hour workshop organized by the Delta Independent Science Board and held at the campus of th

Earthquakes and high water as hazards to Delta levees were reviewed in a seven-hour workshop organized by the Delta Independent Science Board and held at the campus of the University of California, Davis. Earthquake hazards in the Delta were described in terms of ground motions from Bay Area earthquakes, infrequent earthquake recurrence on faults beneath the Delta, and levee fills prone to earthquake-induced liquefaction. Large uncertainties attend all these seismic elements of levee hazard. Those uncertainties, according to presentations in the workshop, include whether the Delta ground motions previously computed for Bay Area earthquakes were too large.  Hazards from high water were deemed greatest from the confluence of high river discharge, wind-driven surge and waves, and high tides. Major risk assessments have used available data on these hazards without mandates to advance the science. Research needs and opportunities identified in the workshop include expanded observations of Delta ground motions, improved estimates of geologically recent displacement on faults beneath the Delta, further identification of liquefiable materials and mechanisms beneath levees, continued airborne measurements of land-level change, updated mapping of the contracting area of remaining peat, and fuller documentation of past levee failures. Recurring assessments of earthquake hazards and climate change provide precedents for periodic reappraisal of Delta levee risk. The workshop brought together different parts of the diverse community of Delta levee specialists. Positive responses to the workshop suggest that it served levee specialists and outsiders alike.

Workshop report—Earthquakes and High Water as Levee Hazards in the Sacramento-San Joaquin Delta

Delta Stewardship Council (Delta Council) | September 30th, 2016

Yolo Bypass Salmonid Habitat Restoration and Fish Passage Final Environmental Impact Statement / Environmental Impact Report (Chapters 9-12)

U.S. Bureau of Reclamation (USBR) | May 1st, 2019

Yolo Bypass Salmonid Habitat Restoration and Fish Passage Final Environmental Impact Statement / Environmental Impact Report (Executive Summary)

U.S. Bureau of Reclamation (USBR) | May 1st, 2019

The Yolo Bypass Salmonid Habitat Restoration and Fish Passage Project (Project) Environmental Impact Statement/Environmental Impact Report (EIS/EIR) addresses methods to

The Yolo Bypass Salmonid Habitat Restoration and Fish Passage Project (Project) Environmental Impact Statement/Environmental Impact Report (EIS/EIR) addresses methods to improve fish passage and increase floodplain fisheries rearing habitat in the Yolo Bypass to benefit Sacramento River winter-run Chinook salmon, Central Valley spring-run Chinook salmon, Central Valley steelhead, and Southern Distinct Population Segment of North American green sturgeon. The Project actions would implement Reasonable and Prudent Alternative actions I.6.1 and I.7, as described in the 2009 National Oceanic and Atmospheric Administration National Marine Fisheries Service Biological Opinion and Conference Opinion on the Long-Term Operations of the Central Valley Project and State Water Project and the 2012 Yolo Bypass Salmonid Habitat Restoration and Fish Passage Implementation Plan.  This EIS/EIR has been prepared according to requirements of the National Environmental Policy Act and the California Environmental Quality Act. Direct, indirect, and cumulative impacts resulting from the project alternatives on the environment of the region are evaluated.  Full document files: Chapters 1-8 Chapters 9-12 Chapters 13-26 Appendices and drafts

Yuba-Feather FIRO Final Viability Assessment

California Department of Water Resources (DWR) | March 14th, 2025

This Yuba-Feather Final Viability Assessment (FVA) evaluates whether improved precipitation and runoff forecasts can reduce flood risk downstream of New Bullards Bar (NBB

This Yuba-Feather Final Viability Assessment (FVA) evaluates whether improved precipitation and runoff forecasts can reduce flood risk downstream of New Bullards Bar (NBB), owned and operated by Yuba Water Agency (Yuba Water), and Lake Oroville (ORO), owned and operated by the California Department of Water Resources (DWR). These reservoirs are in the Yuba-Feather watersheds in the Sierra Nevada and eastern Sacramento Valley of Northern California (Figure ES-1 and ES-2). Each reservoirs’ flood risk reduction operations are regulated by United States Army Corps of Engineers (USACE) through Water Control Manuals (WCMs).  Reducing flood risk by making reservoir releases ahead of storms creates additional temporary flood storage space for anticipated inflows but requires confidence and skill in forecasted conditions.