Contributions of Climate Change and ENSO Variability to Future Precipitation Extremes Over California

American Geophysical Union (AGU) | June 14th, 2023

Debris flow occurrence under changing climate and wildfire regimes: A southern California perspective

Geomorphology (Elsevier) | December 2nd, 2022

In southern California, wildfire incidents are increasing in frequency and magnitude. There is a great deal of research predicting the impact of climate change on large s

In southern California, wildfire incidents are increasing in frequency and magnitude. There is a great deal of research predicting the impact of climate change on large scale fire regimes. These impacts, now the new normal, include increases in future fire incidents and burn severities. Yet predictive studies on how ecosystems respond to changing fire regimes are lacking. Identifying trends in post-fire erosion patterns, such as post-fire debris flows, is critical for increasing human resiliency and adaptation to changing weather patterns and eventual long-term climate change. The relative historical abundance of post-fire debris flows in southern California presents this concern: will worsening wildfire regimes result in more post-fire debris flows? Our research addresses this concern by utilizing a descriptive approach to analyze post-fire debris flows in southern California from 2001 to 2018 to elucidate possible trends. We found that 84 % of debris flows originate from watersheds with soils burnt at moderate soil burn severity. We found that debris flow occurrence is more reliant on the percent coverage of a soil burn severity classification than its areal extent. Further, larger fires also tended to produce more debris flows and most (73 %) debris flow watersheds occurred in predominantly bedrock areas. Our research suggests that the number of post-fire runoff-generated debris flows in the region will increase if fires continue to increase in size, occur on slopes of at least 20°, burn south-facing watersheds with bedrock of igneous or sedimentary origin to at least a moderate severity, and peak rainfall intensity return intervals do not change. These findings highlight the interconnectivity between natural erosive processes, wildfires, humans, and climate change.

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.

Delta Adapts: Creating a Climate Resilient Future

Delta Stewardship Council (Delta Council) | June 25th, 2021

The time to act is now. Climate change is already altering the physical environment of the Sacramento–San Joaquin Delta and Suisun Marsh (Delta), and we will continue t

The time to act is now. Climate change is already altering the physical environment of the Sacramento–San Joaquin Delta and Suisun Marsh (Delta), and we will continue to experience its effects through hotter temperatures, more severe wildfires, and prolonged droughts. Over the long term, climate change in the Delta is expected to harm human health and safety, disrupt the economy, diminish water supply availability and usability, shift ecosystem function, compromise sensitive habitats, and increase the challenges of providing basic services. Many of these impacts will disproportionately affect vulnerable communities. Although the exact extent and timing of these impacts is uncertain, this climate change vulnerability assessment phase of Delta Adapts will help the Delta Stewardship Council (Council) understand specific regional climate risks and vulnerabilities. Regional, collaborative adaptation strategies rooted in science are more critical than ever. The next phase of Delta Adapts, preparing an adaptation strategy, will identify ways to address the risks and vulnerabilities.

Delta Levee Investment Strategy: Final Report

Delta Stewardship Council (Delta Council) | August 4th, 2017

In the California Sacramento-San Joaquin Delta (Delta), levee failure could cause catastrophic flooding, potentially causing injury or loss of life, and possibly damaging

In the California Sacramento-San Joaquin Delta (Delta), levee failure could cause catastrophic flooding, potentially causing injury or loss of life, and possibly damaging property, water supply, infrastructure, and environmental resources of importance to the entire State of California (State). Though levee maintenance and improvements over the past three decades have reduced the frequency of levee failures, the State has no comprehensive method to prioritize its investments in Delta levees operations, maintenance, and improvement projects. The Delta Plan, adopted on May 16, 2013, recommends that the Delta Stewardship Council (Council), in consultation with the California Department of Water Resources (DWR), the Central Valley Flood Protection Board (CVFPB), the Delta Protection Commission (DPC), local agencies, and the California Water Commission, implement California Water Code (CWC) section 85306 by developing a Delta Levees Investment Strategy (DLIS) to identify funding priorities for State investments in Delta levees. The DLIS is an innovative approach for determining priorities for State funds for levee improvement in the Delta and Suisun Marsh. The DLIS, which considers the assets protected by levees, the threats to levees, and the multiple beneficiaries of levee investments, uses a risk analysis methodology to recommend priorities for State investments in levee operations, maintenance, and improvements. This methodology was developed in close coordination with State agency partners, local and regional flood management and emergency response planning agencies, and other interested parties. In total, the Council worked with 113 different stakeholders and conducted 10 public meetings, 60 stakeholder outreach meetings, and 60 interagency coordination meetings. The Council also discussed DLIS issues at 38 Council meetings and workshops, which provided opportunities for public comment. The DLIS team developed a Decision Support Tool (DST) to enable the Council and stakeholders to review and update the data and analysis that form the basis of the risk evaluation. The DST supports deliberations by summarizing information about baseline and future risks, aggregating and displaying risks, and then identifying portfolios of investments that have the potential to reduce risk to State interests. The data components in the DST are designed to be updated as new information is collected or identified.

Delta Levee Investment Strategy: Risk Analysis Methodology

Delta Stewardship Council (Delta Council) | July 20th, 2016

Levees in California’s Sacramento-San Joaquin Delta (Delta) reduce flood risk to people, property, natural resources, and infrastructure systems of statewide importance

Levees in California’s Sacramento-San Joaquin Delta (Delta) reduce flood risk to people, property, natural resources, and infrastructure systems of statewide importance. Levee failure (such as a levee breach) could cause devastating flooding, potentially resulting in injury or loss of life, damage to property and infrastructure, disruption of water supply, and harm to environmental resources of statewide significance. Currently, the State of California (State) does not have a long-term strategy to guide future investments of its limited funding for Delta levees. The 2009 Delta Reform Act directed the Delta Stewardship Council (Council) to lead the effort to develop and recommend priorities for State investments in Delta levees to reduce flood risks and to advance the coequal goals of water supply reliability and restoring the Delta ecosystem. Working closely with other agencies and the public, the Council is developing a Delta Levees Investment Strategy (DLIS) to establish priorities for State investments in the Delta levee system. Risk, the potential for an unwanted outcome, is a principal factor in establishing priorities for State investments in levees. Specifically, risk is the probability that an adverse event (such as a flood or earthquake) will occur multiplied by the consequences of that event: Risk = Probability x Consequences As presented in this report, the DLIS is based on a comprehensive methodology that quantifies risk by considering the threats to Delta levees and the assets protected by Delta levees. The DLIS also considers the multiple beneficiaries of Delta levee investments. Building on the results of previous Delta levee planning efforts, the DLIS collects and uses the best available existing data and information from numerous sources to evaluate risks to State interests in the Delta as defined by risk to public safety; property and infrastructure; water supply reliability; the Delta ecosystem; and the unique attributes of the Delta as an evolving place. The DLIS evaluates those risks under current and potential future conditions. In early 2015, the DLIS team prepared an Interim Progress Report summarizing the work conducted during the first 9 months of the DLIS project. The report focused primarily on the methodologies planned for implementing the DLIS project to facilitate a “mid-course” review by an independent science panel, which completed its work in July 2015. Panel members offered comments for improvement and concluded that the “overall methodology of using existing data, identifying important metrics, aggregating results, and making comparisons across islands is conceptually sound” (Mitchell et al. 2015). The DLIS project includes outreach to State and local agencies, concerned stakeholders in the Delta, knowledgeable technical resources, owners and operators of Delta infrastructure, and Delta leaders and residents. The final methodologies employed in the DLIS project are reported herein and incorporate the input from the independent science panel as well as feedback and comments resulting from the outreach efforts.

Delta Levees Investment Strategy: Sea Level Rise Methodology

Delta Stewardship Council (Delta Council) | August 21st, 2015

This memorandum describes the methodology used to account for the impact of potential future sea level rise on the Delta Levees Investment Strategy (DLIS) metrics and how

This memorandum describes the methodology used to account for the impact of potential future sea level rise on the Delta Levees Investment Strategy (DLIS) metrics and how those impacts are incorporated into the DLIS planning tool. A description of the approach used to account for the spatial variation of tide effects in the Delta and Suisun Marsh and prediction uncertainties are also included in this memorandum.

Desalination and sustainability - An appraisal and current perspective

Water Research, Elsevier | February 1st, 2016

Desalination technologies have evolved and advanced rapidly along with increasing water demands around the world since 1950s. Many reviews have focused on the techno-econ

Desalination technologies have evolved and advanced rapidly along with increasing water demands around the world since 1950s. Many reviews have focused on the techno-economic and environmental and ecological issues of the desalination technologies and emphasized the feasibility of desalination industry as an alternative to meet the water demands in many water scarce regions. Despite these efforts, many perceptions about desalination processes hinder their applications for potential water supplies. This article has two specific aims: 1) provide an overview of the desalination trends around the world and discuss the sustainability components of desalination processes in comparison with other water supply alternatives; and 2) discuss case studies for desalination, and drivers and factors that influence sustainable desalination and other alternative water sources for desalination to increase our current understanding on the sensitive and futuristic issues of water supply and resource management options for drought facing regions. Although some of the facts and recent developments discussed here show that desalination can be affordable and potentially sustainable, contributions that meaningfully address socio-economic and ecological and environmental issues of desalination processes are urgently required in this critical era of severe water stress for the present context and the future development of desalination technologies.

Design Life Level: Quantifying risk in a changing climate

American Geophysical Union (AGU) | September 23rd, 2013

In the past, the concepts of return levels and return periods have been standard and important tools for engineering design. However, these concepts are based on theassu

In the past, the concepts of return levels and return periods have been standard and important tools for engineering design. However, these concepts are based on theassumption of a stationary climate and do not apply to a changing climate, whether local orglobal. In this paper, we propose a refined concept, Design Life Level, which quantifies risk in a nonstationary climate and can serve as the basis for communication. In current practice, typical hydrologic risk management focuses on a standard (e.g., in terms of a high quantile corresponding to the specified probability of failure for a single year). Nevertheless, the basic information needed for engineering design should consist of (i) the design life period (e.g., the next 50 years, say 2015–2064); and (ii) the probability (e.g., 5% chance) of a hazardous event (typically, in the form of the hydrologic variable exceeding a high level) occurring during the design life period. Capturing both of these design characteristics, the Design Life Level is defined as an upper quantile (e.g., 5%) of the distribution of the maximum value of the hydrologic variable (e.g., water level) over the design life period. We relate this concept and variants of it to existing literature and illustrate how they, and some useful complementary plots, may be computed and used. One practically important consideration concerns quantifying the statistical uncertainty in estimating a high quantile under nonstationarity.

Development of Stage-Frequency Curves in the Sacramento-San Joaquin Delta for Climate Change and Sea Level Rise

California Energy Commission (CEC) | August 27th, 2018

Future changes in hydrologic patterns and sea level rise will impact water levels in the Sacramento-San Joaquin Delta (Delta), the hub of California’s water supply sys

Future changes in hydrologic patterns and sea level rise will impact water levels in the Sacramento-San Joaquin Delta (Delta), the hub of California’s water supply system and an important ecosystem and agricultural area. An important tool for flood management is stage frequency curves which indicate how often certain water levels (or stage) occur. The Delta poses inherent complexity in the determination of stage-frequency and requires a number of considerations. One needs to account for river flows coming into the Delta, as well as the effect of tides from the Delta’s connection to the ocean through San Francisco Bay. During storms, Delta water levels are also affected by storm surge from the advancing storm fronts coming from the Pacific Ocean. Under climate change, Delta water levels will also be affected by rising sea levels and expected changes in hydrology, such as shifts in timing and amount of precipitation and runoff and changes in how much of our precipitation falls as rain or snow (referred to as climate change hydrology in this paper). With these taken into consideration, this study lays out the assumption and method used to develop stage-frequency curves in the Delta for three different conditions: current hydrology conditions, current hydrology with sea level rise, and late-century climate change hydrology with sea level rise. In addition, water surface elevation profiles along the Sacramento and San Joaquin rivers for various magnitudes of flood events were compared to the top of levee elevations. Both the stage-frequency curves and the water surface elevation profiles comparisons to top of levee elevations provide valuable information to water resources planners and were applied to inform life and flood risk analysis for the Delta in the Central Valley Flood Protection Plan 2017 Update.