Decision Scaling Evaluation of Climate Risks to the State Water Project

California Department of Water Resources (DWR) | May 29th, 2019

This Final Decision Scaling Vulnerability Assessment Report updates and describes a joint endeavor of the California Department of Water Resources (DWR) and the Universit

This Final Decision Scaling Vulnerability Assessment Report updates and describes a joint endeavor of the California Department of Water Resources (DWR) and the University of Massachusetts, Amherst (UMass) to improve planning for the uncertain effects of climate change on the California Central Valley Water System (CVS)1 by integrating vulnerability-based analysis with traditional risk-based assessment methods. This report summarizes the research goals, analytical approach, workflow of modeling tools, evaluation of alternative experimental designs, refined strategy for data visualization, and assessment of the vulnerability of the CVS to climate change.  This report begins with a review of historical and projected climate change in California, which includes descriptions of several DWR-UMass team investigations of historical records, observed climate trends, and many climate projections for the CVS, specifically. The next section of this report summarizes the work previously accomplished by the academic community, the government, and the community of water resources practitioners evaluating climate change-related risks to the CVS.  With that background in place, this report explains the methodology developed for this study (illustrated in Figure ES1) and provides details on each sub-step of the process. Whereas previous studies have tested the response of some aspect of the California water system to ahistorical climate traces, the decision scaling approach adopted for this study allows systematic assessment of the vulnerability of the entire (interconnected and complex) CVS to a wide range of potential future climate conditions, and quantification of the significance of climate shift relative to natural (and climate-change-amplified) variability. The climate response function that results from the decision scaling approach depicts expected water system performance relative to historical performance across a range of climate changes. An important benefit of this approach is the ability to use a variety of climate information sources to assess the level of concern to assign to the vulnerabilities that are identified. Consequently, climate information, including climate change projections and formal probability estimates, can be used as a sensitivity factor when assessing risk, rather than the driver of the analysis. This allows discussion of risk and opportunity (each a function of impact and likelihood) in water system investment.  This assessment of long-term and persistent hydrologic impacts of climate change focuses on the effects to the operation of the State Water Project (SWP), including ecological conditions that dictate operating rules. DWR owns and operates the SWP for flood control, maintenance of environmental and water quality conditions, water supply, hydropower, and recreation. Consequently, analysis of SWP performance under climate-changed conditions yields an array of impact metrics across these areas of concern. The analysis focuses on persistent medium- and long-term conditions evaluated at a monthly time-step. Short-duration extreme precipitation events that cause flooding may also stress water resource management but are beyond the scope of this study.  This study has adopted CalLite 3.0 to simulate the coordinated operations of the Central Valley Project (CVP) and SWP under a wide range of climate possibilities. Climate traces are developed through coupling historical daily temperature and precipitation (1950–2013) (Livneh et al. 2013) to the paleo-dendrochronological reconstructed streamflow record of the Sacramento-4-river annual streamflow (900–2013) (Meko et al. 2014). An advanced hydrologic model, the Sacramento Soil Moisture Accounting distributed hydrologic model (SAC-SMA-DS), translates the hydroclimatic traces into streamflow, which are the key inputs to the water system model.

Decoupling outmigration from marine survival indicates outsized influence of streamflow on cohort success for California’s Chinook salmon populations

Canadian Journal of Fisheries and Aquatic Sciences (Canadian Science Publishing) | October 17th, 2018

Historically, marine survival estimates for salmon have been confounded with freshwater seaward migration (outmigration) survival. Telemetry studies have revealed low and

Historically, marine survival estimates for salmon have been confounded with freshwater seaward migration (outmigration) survival. Telemetry studies have revealed low and variable survival during outmigration, suggesting marine mortality may not be the primary source of variability in cohort size as previously believed. Using a novel combination of tagging technologies, survival during these two life stages was decoupled over 5 years for Sacramento River Chinook salmon (Oncorhynchus tshawytscha). Outmigration survival ranged from 2.6% to 17%, and marine survival ranged from 4.2% to 22.8%. Influential environmental drivers in both life stages were also compared with smolt-to-adult ratios (SAR) for three Chinook salmon populations over 20 years. Streamflow during outmigration had higher correlation with SAR (r2 > 0.34) than two marine productivity indices (r2 < 0.08). The few SAR estimates that were poorly predicted by flow occurred during years with the lowest marine productivity, suggesting most interannual SAR fluctuations are explained by outmigration survival, but abnormally poor marine conditions also reduce SAR. The outsized influence of flow on SAR provides managers with a powerful mitigation tool in a watershed where flow is tightly regulated.

Defining Snow Drought and Why It Matters

American Geophysical Union (AGU) | February 28th, 2017

On 12 February, water resource managers at the Oroville Dam issued an evacuation warning that forced some 180,000 Californians to relocate to higher ground. The story of

On 12 February, water resource managers at the Oroville Dam issued an evacuation warning that forced some 180,000 Californians to relocate to higher ground. The story of how conditions got to this point involves several factors, but two clearly stand out: the need to prevent water shortages during a record drought, followed by one of the wettest October–February periods in California history.

Delta Adapts: Creating a Climate Resilient Future

Delta Stewardship Council (DSC) | June 25th, 2025

The Delta Stewardship Council (Council) was established, in part, to provide sustainable management for the Delta ecosystem, and climate adaptation is a critical consider

The Delta Stewardship Council (Council) was established, in part, to provide sustainable management for the Delta ecosystem, and climate adaptation is a critical consideration to achieve that mission in future decades. To respond to the challenge of climate adaptation,the Council developed this initiative, Delta Adapts: Creating a Climate Resilient Future (Delta Adapts). Climate change must be considered to attain the state’s coequal goals, as established by the 2009 Delta Reform Act: securing a reliable water supply for California, protecting and restoring the ecosystem and wildlife it supports, and enhancing the Delta as a unique place, with its community, tribal, and agricultural heritage. The Council adopted the Delta Plan, which has regulatory policies that protect land for restoration and agriculture, help manage flood risk, and improve water supply reliability. The Delta Plan directs the Council to guide and regulate actions of the 200+ state and local agencies in the Delta to ensure they support statewide water supply reliability and Delta ecosystem restoration.

Delta Conveyance Project Fall 2023

California Department of Water Resources (DWR) | September 13th, 2023

Delta Conveyance Project Final Environmental Impact Report

California Department of Water Resources (DWR) | December 8th, 2023

Delta Conveyance Project Operations Plan

California Department of Water Resources (DWR) | August 23rd, 2024

This document presents a summary of the Delta Conveyance Project (DCP) operations commitments that the Department of Water Resources (DWR) has made for when the DCP becom

This document presents a summary of the Delta Conveyance Project (DCP) operations commitments that the Department of Water Resources (DWR) has made for when the DCP becomes operational.

Delta Conveyance Project: Modernizing California’s Water Infrastructure, Fast Facts 2024

California Department of Water Resources (DWR) | September 13th, 2023

Delta Fish Agreement

California Department of Fish and Wildlife (CDFW) | December 30th, 1986

On December 30, 1986, the Directors of CDFW and the Department of Water Resources (DWR) signed an agreement to provide for offsetting fishery impacts caused by the divers

On December 30, 1986, the Directors of CDFW and the Department of Water Resources (DWR) signed an agreement to provide for offsetting fishery impacts caused by the diversion of water at the Harvey O. Banks Delta Pumping Plant (Banks), located at the head of the California Aqueduct near Tracy, California. The agreement, currently referred to as the Delta Fish Agreement (DFA or Agreement) (PDF), was previously known as the Delta Pumping Plant Fish Protection Agreement or Four Pumps Agreement because it was adopted as part of the mitigation package to add four additional pumps to Banks during the late 1980’s. Direct losses of Chinook salmon, steelhead, and striped bass are offset or mitigated through the funding and implementation of fish mitigation projects.

Delta Independent Science Board -- Comments on the Sacramento / Delta Draft Staff Report

Delta Stewardship Council (Delta Council) | January 19th, 2024