Theme for 2023:
Water Management Options for Adapting to California Droughts and Floods
University of California, Davis
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About This Symposium
Climate change impacts are altering our historic understanding of meteorology and hydrology. When, where, and how much precipitation falls is changing. In recent years, floods and droughts are more extreme than historic records show. Climate models looking forward show increasing flood and drought extremes. We use the best available data at the time when making decisions. Adoption of the 2022 Update of the Central Valley Flood Protection Plan in December 2022 brings our attention to thinking about options for integrated management of floods and droughts.
Special Recognition Award
The 2023 Special Recognition Award was presented to Michael L. Anderson, Ph.D., P.E.. See the award language and hear the presentation on the Symposium's Mike Anderson award page.
Is the Drought Over? Which Drought?
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Twice in just a decade, California has transitioned from multi-year severe droughts to extreme wet years. Such whiplash climate may create the notion than in years of extreme high precipitation, the seemingly abundance of surface water may have offset the impacts of multi-year precipitation deficit. Yet droughts affect natural and human systems differently, and as slowly occurring events, drought impacts extend over longer periods of time compared to the expeditious course of most floods. And just to compound the conundrum of common drought indicators that give a sense of its status, the often invisible and lingering effects of prolonged droughts are on ecosystems and rural communities.
We present lessons learned from recent droughts in California with an assessment on their impacts short and longer term in various sectors including agriculture, cities, communities and ecosystems. Some of the common drought indicators are discussed in the context of manmade and natural systems which provide a drought buffer to the water demanding sectors and the vulnerabilities and risks associated with drought. Potential and insights from water trading, stress irrigation, and water storage in agriculture, the largest water user in the era of the Sustainable Groundwater Management Act (SGMA), are presented. The use of post-disciplinary systems analysis and modeling in assessing drought status and impacts is discussed to support management and policy insights to improve planning and preparedness for future California climate extremes.
Western Aridification and Climate Change Impacts in California
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Climate change has shifted the distribution of spatial and seasonal water while at the same time warming has induced greater evapotranspiration, water demand, and declining soil moisture. Although there are occasional wetter years than historically, these impacts can lead to aridification, which is a gradual change of a region to a long-term drier climate. This process leads to changes in vegetation, loss of forests to shrubs, and changes in habitat. Western US has undergone some slight aridification over the last 40 years, but future projections indicate more long-term changes. These shifts are accelerating in the southwest US with long term droughts that require resource management to adapt to changes in water resources for long term resiliency.
Monitoring is critical to understanding antecedent conditions and validating models that simulate near-term and long-term forecasting and provide trend analyses. Important variables to monitor are snow, soil moisture, evapotranspiration, and streamflow. Modeling allows us to look at longer term spatially distributed processes. We will explore where less rain is falling as snow and how that impacts whether recharge or runoff dominates. We will also demonstrate that warmer rains in spring are resulting in faster snowmelt. Long term changes in evaporative demand are decreasing seasonal soil moisture, which means it takes more precipitation or snow melt to initiate springtime runoff.
Keeping the water in the watershed is a key to healthy watersheds and forests and promoting opportunities for increasing recharge that can sustain baseflows and groundwater is critical. Understanding how and where processes are changing can highlight where priority attention can be paid to devising adaptation strategies.
DWR Program Update: Aerial Remote Sensing of Snow and Snowmelt Forecasting
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Adapting to climate change requires changing the way the Department of Water Resources (DWR) observes and forecasts weather and hydrologic conditions. Historical patterns and relationships between precipitation, snowpack, and streamflow that have been used to anticipate how much water will run off for beneficial use have shown vulnerabilities. While DWR's observation and forecasting programs have a long history of partnerships with the research community to bring relevant research advances into program operation, the pace and scale of extremes necessitate acceleration of recent and ongoing advances to ensure a forecasting framework that can adapt at the pace of a changing climate.
The California Cooperative Snow Surveys, which DWR leads, has been working with the research community to develop an operational framework for climate resilient forecasting that focuses on two goals.
- Transition from index-based statistical forecasting tools, such as linear regression of precipitation, snowpack, and runoff indices, to spatially explicit, physically based, and climate informed modeling tools such as watershed models that simulate the physical processes of snow accumulation and melt and can incorporate forecasts.
- Create an integrated forecast platform that allows easier visual inspection of observed conditions and a customizable decision support dashboard that connects observations, high resolution near-term forecasting, standard weather forecasting, week 2 to 4 outlooks, sub-seasonal to seasonal outlooks, and water year outlooks.
This presentation will detail the Aerial Remote Sensing of Snow (ARSS) Program's activities during Water Year 2023 and the roadmap for a climate resilient forecasting framework as the program evolves.
How are Groundwater and Surface Water Connected?
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Groundwater, which constitutes 97% of all liquid freshwater on Earth, and surface water are integrally connected. Groundwater serves as a vast 'reservoir' that can sustain stream baseflow when aquifers are sufficiently full, and can receive substantial amounts of recharge from surface water bodies when aquifers are depleted. A prime example is the transition of the Central Valley from a landscape rich in wetlands (~20%) in the first half of the 20th century to just ~2% wetlands currently. This transition occurred mainly due to extensive groundwater pumping that reversed the direction of groundwater and surface water interaction from upward (discharge to the surface) to downward (recharge). The groundwater depletion has created opportunities for vastly increasing subsurface storage via, for example, Flood-MAR (flood managed aquifer recharge).
Studies conducted during 2014-2020 by UC Water (University of California Water Security and Sustainability Research Initiative) demonstrated the strong potential for Flood-MAR in the American-Cosumnes Basin. They showed that by diverting only about half the total floodwaters hydrologically available for recharge over a 20-year period such that Delta outflow requirements are never violated, about 5.4 MAF could have been recharged, resulting in significant increases in groundwater storage (3.7 MAF), streamflow (0.87 MAF) and flow to adjacent basins (0.89 MAF). Concurrently with that work, Sacramento Area Flood Control Agency (SAFCA) in its long-range planning for climate change revealed plans to retrofit Placer County Water Agency (PCWA) and Sacramento Municipal Utility District (SMUD) dams upstream of Folsom Lake to release more water in winter, in turn providing added motivation and benefit for a Flood-MAR strategy.
A key to greater water security under ongoing climate change and more extreme weather is the advanced integration of both surface water and groundwater 'reservoirs' to maximize total water storage in ways that benefit both humans and ecosystems.
Adaptive Water Management for California's Changing Climate
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The narrative of climate change speaks to warmer temperatures, more rain, less snow, greater variability and greater extremes all of which will have an impact on water management in California. The past decade has provided early glimpses of what this might look like as a number of novel extremes have been experienced. As climate change continues to evolve, the extremes are expected to become episodic and then commonplace. Adapting to changing conditions requires the ability to detect change and its impact on water management. It is also important to identify the consequences of change as well as options to address those consequences. Finally, metrics that facilitate the understanding of when and how to implement adaptations need to be developed.
At the California Department of Water Resources, a significant effort has been in play over the past decade in collaboration with the research community to develop these capabilities. This talk will highlight efforts and products developed and directions for future efforts. Some key examples are work with a stochastic weather generator to translate climate information from global climate change models to weather sequences for hydrologic and water management analyses and for analyses supporting our understanding of evolving flood risk in the Central Valley Flood Protection Plan.
Panel Discussion: Anticipating Consequences of Floods and Droughts
Managed Aquifer Recharge as a Tool to Enhance Sustainable Groundwater Management in California
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Within the last 12 months, California has experienced one of the most severe drought and flood years of the last decades. Water abundance caused by above average precipitation and an exceptional snowpack call for widespread action to capture more water to underground storage to address long-term groundwater overdraft and state mandates to achieve groundwater sustainability by 2040. However, despite growing awareness, groundwater recharge efforts have not yet reached their full potential to counterbalance growing groundwater depletion.
To capture more flood water to underground storage in exceptionally wet years like this one, on-farm recharge provides a cost-effective alternative to dedicated recharge systems such as infiltration basins, because it allows spreading large volume flows on vast areas of agricultural lands. Yet, knowledge gaps, synergies, and tradeoffs in on-farm recharge research still exist hindering wider adoption.
In this talk we reflect on the opportunities of this wet year for groundwater recharge and evaluate some of the barriers and knowledge gaps prohibiting larger use of agricultural lands for groundwater recharge. We will evaluate water quality impacts, crop health and yield, and showcase the multidisciplinary approach needed for communication and coordination of agricultural managed aquifer programs with stakeholders and the public to develop a framework for large-scale implementation.
Floodplain Expansion for Increasing Groundwater Storage and Reducing Floods
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The Central Valley of California has lost 95% of its wetland habitats since the Gold Rush (1848), and along with it, our resilience to drought and flood. We called it the period of "reclamation" — creating new land from floodplains with levees. We disconnected watershed processes and greatly increased our collective vulnerability to extreme precipitation damages. Our state's variable hydrology will increase in severity in the coming decades with dramatic swings from long and hot dry spells to rapid deluges that overwhelm our constructed water infrastructure. This will thrust floodplain reconnection and aquifer replenishment (along with radical demand reduction) into a core position in our climate resilience planning.
Reconnecting rivers and floodplains is a water solution with potential to help many of our farms, wildlife species and communities. Looking ahead, we need to increase on a larger and faster scale expanded floodplains. Based on experience, Julie shares River Partners' lessons learned about how we can design and deliver floodplain reconnection projects and programs, address the challenges to delivery, and scale it up across the valley rapidly and carefully. This talk will use stories from Central Valley floodplain reconnection projects that store water and reduce flood risk to illustrate 3 major themes:
- Some obstacles to scaling require time and care to consider — not least of which are issues of equity, ownership, and self-determination for communities at the front lines of climate change;
- Taking action in the face of uncertainty and navigating bureaucracy for efficient action is not comfortable for most of us, especially with so much at stake, including potential species extinction; and
- Our elected officials and administration leaders are eager to support winning solutions, but often can't influence the depth of the social system obstacles that keep us from scaling up broadly-supported and integrated water solutions within an effective timeframe. Solutions will be suggested.
DWR's Basin Characterization: Statewide AEM Surveys and Recharge Pilot Study
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As part of DWR's requirement to update California's Groundwater (Bulletin 118) and characterize groundwater basins across the state, DWR is initiating a Basin Characterization Program to collect and analyze AEM and other data to support SGMA implementation initiatives and standardized statewide datasets. Under this Program, DWR developed the Statewide Airborne Electromagnetic (AEM) Survey Project to collect AEM data in California's high- and medium-priority groundwater basins. The Project started in 2021 and data collection is expected to be complete by Fall 2023. Data and reports are published on the CNRA Open Data Portal and novel tools were developed to allow the public to easily visualize and access data.
As a part of the continued data collection effort under this Program, DWR will be conducting a series of SGMA Implementation Pilot Studies to support groundwater sustainability initiatives. The first Pilot Study will focus on groundwater recharge, floodplain rehabilitation, and domestic wells. The study area is located on the eastern side of the Kings and Madera subbasins, concentrated along the Upper San Joaquin and Fresno Rivers. The Pilot Study includes collection of infill AEM followed by ground-based surveys. The results from the Pilot Study are expected to be available by late 2023/early 2024.
Under the Basin Characterization Program, DWR will develop tools that integrate all existing data (AEM, lithology logs, e-logs, etc.) to create statewide texture and hydrostratigraphic models that address SGMA implementation initiatives. DWR will also be publishing a series of maps and tools to support data analysis. The first of these maps have now been published on the SGMA Data Viewer and show AEM Depth Slices and the Shallow Subsurface Average. These maps aid in delineating the geometry of large-scale features and support identification of potential recharge areas, where the top ~50 feet is dominated by coarse-grained materials.
The Sacramento Regional Water Bank — Uniting Surface Water and Groundwater
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Over the past several decades, Sacramento area local water providers have improved water supply reliability through conjunctive use efforts, increasing water use efficiency, and expanding recycled water use. However, California's highly variable water supplies and climate change present ongoing challenges and uncertainty. For this reason, water providers in the Sacramento region will be expanding conjunctive use efforts through the development of the Sacramento Regional Water Bank (Water Bank). The Water Bank is an innovative groundwater storage program that will improve regional water supply reliability in the near-term and into the future. This climate adaptation strategy will increase our region's resiliency and benefit our local water supply reliability, economy, and environment.
The Sacramento region's unique setting — at the confluence of the Sacramento and American rivers near Folsom Reservoir and overlying the North American and South American groundwater subbasins — is ideal for the Water Bank's development. The Water Bank will allow the region to sustainably increase use of groundwater as a local water source during dry periods, allowing reduced surface water diversions to help meet local environmental needs. In addition, the region's location north of the Sacramento–San Joaquin Delta provides potential opportunities to collaborate and develop solutions to benefit the environment and communities downstream after local needs are met.
The FIRO Balancing Act: Considerations for Forecast Informed Reservoir Operations at Multi-Objective Reservoirs
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This presentation describes the nature of Forecast Informed Reservoir Operations (FIRO) as both a flexible operational strategy for multiple water management objectives and a collaborative research-to-operations partnership integrating federal, state, and local agencies with academic organizations. In recognition of the increasing challenges to water management nationwide, FIRO has been emphasized as a promising approach that can leverage improvements in observational networks and forecasting technologies to potentially reduce the peak and duration of flood flows and enhance water supply reliability. Nationwide efforts are underway to identify optimal candidates for FIRO. Early results of the screening process developed by the Corps' Engineering Research and Development Center (ERDC) are compared to ongoing pilot projects before a deeper dive into the New Bullards Bar Reservoir on the Yuba River.
We present a comparison of existing Water Control Plans (WCP) typical of western reservoirs to build a case for use of forecasts in specifying target flood reserves. The flood reserves depicted range from seasonally-invariant to highly tuned for rainflood runoff, snowmelt, or both. For WCPs based on a basin wetness, precipitation, or inflow index, the streamflow forecasts issued by the California Nevada River Forecast Center (CNRFC), offer superior integration of antecedent conditions with future meteorological uncertainty and watershed response. However, some reservoirs already indicate seasonal forecasts are to be used for this purpose. Both short-range and long-term forecasts can be evaluated to determine the risks associated with selectively releasing or retaining water at the reservoir.
Candidate FIRO alternatives for the New Bullards Bar FIRO program and Water Control Manual update include a FIRO space that spans portions of both flood control and conservation space. We discuss an operational approach developed through the FIRO preliminary viability assessment (PVA) that relies on a forecast-informed storage guide curve with details of implementation, hypothetical frequency of FIRO activation, key regimes of the operation, and reflections on limitations introduced by competing objectives. The adaptive strategy works with the proposed Atmospheric River Control Spillway to provide greater flexibility to address the changing seasonality and magnitude of weather extremes.
Panel Discussion: Adaptation Options for Managing Floods and Droughts
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