Colorado River

2023 Drinking Water Needs Assessment

California State Water Resources Control Board (SWRCB) | April 30th, 2023

The Needs Assessment is comprised of four core components: the Failing Water System List (Failing list), the Risk Assessment, the Cost Assessment, and the Affordability A

The Needs Assessment is comprised of four core components: the Failing Water System List (Failing list), the Risk Assessment, the Cost Assessment, and the Affordability Assessment. Public input that the State Water Board received via workshops held in 2022 and February 2023 helped improve the 2023 Needs Assessment.

2023 Water Resilience Portfolio Progress Report

California Natural Resources Agency (CNRA) | October 31st, 2023

21st century California drought risk linked to model fidelity of the El Niño teleconnection

Nature Portfolio (Springer Nature) | September 3rd, 2018

Greenhouse gas-induced climate change is expected to lead to negative hydrological impacts for southwestern North America, including California (CA). This includes a decr

Greenhouse gas-induced climate change is expected to lead to negative hydrological impacts for southwestern North America, including California (CA). This includes a decrease in the amount and frequency of precipitation, reductions in Sierra snow pack, and an increase in evapotranspiration, all of which imply a decline in surface water availability, and an increase in drought and stress on water resources. However, a recent study showed the importance of tropical Pacific sea surface temperature (SST) warming and an El Niño Southern Oscillation (ENSO)-like teleconnection in driving an increase in CA precipitation through the 21st century, particularly during winter (DJF). Here, we extend this prior work and show wetter (drier) CA conditions, based on several drought metrics, are associated with an El Niño (La Niña)-like SST pattern. Models that better simulate the observed ENSO-CA precipitation teleconnection also better simulate the ENSO-CA drought relationships, and yield negligible change in the risk of 21st century CA drought, primarily due to wetting during winter. Seasonally, however, CA drought risk is projected to increase during the non-winter months, particularly in the models that poorly simulate the observed teleconnection. Thus, future projections of CA drought are dependent on model fidelity of the El Niño teleconnection. As opposed to focusing on adapting to less water, models that better simulate the teleconnection imply adaptation measures focused on smoothing seasonal differences for affected agricultural, terrestrial, and aquatic systems, as well as effectively capturing enhanced winter runoff.

A 350,000-year history of groundwater recharge in the southern Great Basin, USA

Nature Portfolio (Springer Nature) | March 31st, 2023

Estimating groundwater recharge under various climate conditions is important for predicting future freshwater availability. This is especially true for the water-limited

Estimating groundwater recharge under various climate conditions is important for predicting future freshwater availability. This is especially true for the water-limited region of the southern Great Basin, USA. To investigate the response of groundwater recharge to different climate states, we calculate the paleo recharge to a groundwater basin in southern Nevada over the last 350,000 years. Our approach combines a groundwater model with paleo-water-table data from Devils Hole cave. The minimum water-table during peak interglacial conditions was more than 1.6 m below modern levels, representing a recharge decline of less than 17% from present-day conditions. During peak glacial conditions, the water-table elevation was at least 9.5 m above modern levels, representing a recharge increase of more than 233–244% compared to present-day conditions. The elevation of the Devils Hole water-table is 3–4 times more sensitive to groundwater recharge during dry interglacial periods, compared to wet glacial periods. This study can serve as a benchmark for understanding long-term effects of past and future climate change on groundwater resources.

A Field Guide to the Identification of the Ordinary High Water Mark (OHWM) in the Arid West Region of the Western United States: A Delineation Manual

U.S. Army Corps of Engineers (USACE) | August 1st, 2008

The Ordinary High Water Mark (OHWM) is an approach for identifying the lateral limits of non-wetland waters. However, determining whether any non-wetland water is

The Ordinary High Water Mark (OHWM) is an approach for identifying the lateral limits of non-wetland waters. However, determining whether any non-wetland water is a jurisdictional “Water of the United States” (WoUS) involves further assessment in accordance with the regulations, case law, and clarifying guidance. In the Arid West region of the U.S., the most problematic Ordinary High Water (OHW) delineations are associated with the ephemeral/intermittent channel forms that dominate the Arid West landscape. This report presents a method for delineating the lateral extent of the non-wetland waters in the Arid West using stream geomorphology and vegetation response to the dominant stream discharge.

A Machine Learning Approach to Predict Groundwater Levels in California Reveals Ecosystems at Risk

Frontiers in Earth Science (Frontiers) | December 17th, 2021

Groundwater dependent ecosystems (GDEs) are increasingly threatened worldwide, but the shallow groundwater resources that they are reliant upon are seldom monitored. In t

Groundwater dependent ecosystems (GDEs) are increasingly threatened worldwide, but the shallow groundwater resources that they are reliant upon are seldom monitored. In this study, we used satellite-based remote sensing to predict groundwater levels under groundwater dependent ecosystems across California, USA. Depth to groundwater was modelled for a 35-years period (1985–2019) within all groundwater dependent ecosystems across the state (n = 95,135). Our model was developed within Google Earth Engine using Landsat satellite imagery, climate data, and field-based groundwater data [n = 627 shallow (< 30 m) monitoring wells] as predictors in a Random Forest model. Our findings show that 1) 44% of groundwater dependent ecosystems have experienced a significant long-term (1985–2019) decline in groundwater levels compared to 28% with a significant increase; 2) groundwater level declines have intensified during the most recent two decades, with 39% of groundwater dependent ecosystems experiencing declines in the 2003–2019 period compared to 27% in the 1985–2002 period; and 3) groundwater declines are most prevalent within GDEs existing in areas of the state where sustainable groundwater management is absent. Our results indicate that declining shallow groundwater levels may be adversely impacting California’s groundwater dependent ecosystems. Particularly where groundwater levels have fallen beneath plant roots or streams thereby affecting key life processes, such as forest recruitment/succession, or hydrological processes, such as streamflow that affects aquatic habitat. In the absence of groundwater monitoring well data, our model and findings can be used to help state and local water agencies fill in data gaps of shallow groundwater conditions, evaluate potential effects on GDEs, and improve sustainable groundwater management policy in California.

A Path Forward for California’s Freshwater Ecosystems

Public Policy Institute of California (PPIC) | December 2nd, 2019

Californians rely on freshwater ecosystems for many things: water supply, hydropower, recreation, fisheries, flood risk reduction, biodiversity, and more. These ecosystem

Californians rely on freshwater ecosystems for many things: water supply, hydropower, recreation, fisheries, flood risk reduction, biodiversity, and more. These ecosystems—and the social, economic and environmental benefits they provide—are part of the state’s natural infrastructure. But they are changing in undesirable ways in response to water and land use, pollution, introduction of non-native species, and a changing climate. Declines in native biodiversity are the most direct measure of these changes, with numerous species now protected by state and federal endangered species acts (ESAs) and many times more likely to need protection in future.  For the past 40 years, the ESAs have played a prominent role in managing the state’s freshwater ecosystems. While this approach has prevented extinctions, it also places an emphasis on reducing harm to listed species, rather than improving overall ecosystem condition necessary to recover their populations. And these laws are not forward-looking enough to help species adapt to changing climate and reduce future species listings. This approach also fuels controversy and litigation due to perceptions about trade-offs between species protection and economic uses of land and water.  To maintain the benefits that Californians derive from their freshwater ecosystems—and arrest the decline of native biodiversity—a new approach is needed. We recommend that the state adopt the principles and practices of ecosystem-based management. This involves the simultaneous management of water, land, and organisms to achieve a desired ecosystem condition that benefits both native biodiversity and human well-being. The goal of ecosystem-based planning is to develop a shared vision for the ecosystem, agreement upon a common set of facts, and a unified plan to achieve it. We are not proposing major reforms to state or federal endangered species acts. Rather, we recommend a shift in the way these acts are implemented.  Ecosystem-based management relies on robust governance frameworks that are transparent, collaborative, and supported by science and secure funding. Many programs are starting to adopt its principles and practices, but much more needs to be done. Actions needed to achieve ecosystem-based objectives include setting aside water budgets for the environment and using this water to improve ecosystem condition and create multiple benefits. Binding comprehensive agreements between regulatory agencies, stakeholders, and water users—developed as part of sustainable watershed management plans—should guide implementation. These plans can be used to align agency actions and permitting and can be adopted by the State Water Board as water quality control plans.  California needs to change course in how it manages freshwater ecosystems to protect the many beneficial uses they provide. Ecosystem-based management offers a more comprehensive, flexible, and adaptive approach, and one that is compatible with existing laws. We believe this approach is better able to improve ecosystem outcomes that benefit both people and nature and respond to today’s challenges while preparing for an uncertain future. 

A Salton Sea Chronology (Prehistory-2015)

U.S. Bureau of Reclamation (USBR) | January 14th, 2016

A Spatial Hedonic Analysis of the Housing Market around a Large, Failing Desert Lake: The Case of the Salton Sea in California

Journal of Environmental Planning and Management (Taylor & Francis) | March 2nd, 2018

Many lakes around the world exhibit acute environmental stress due to water transfers, persistent droughts, and polluted runoff. In addition, falling water levels worsen

Many lakes around the world exhibit acute environmental stress due to water transfers, persistent droughts, and polluted runoff. In addition, falling water levels worsen air quality by exposing desiccated shores. To our knowledge, however, no published hedonic study has analyzed the costs of deteriorating water quality jointly with the air quality impacts of falling water levels for a large inland water body. We conduct such an analysis for the Salton Sea, the largest lake in California. Our spatial autoregressive models estimated on single-family properties located within 10 miles (16.1 km) of the Sea show that a 1 km reduction in distance to the Sea results in a $595 decrease in the price of a single-family residence. In addition, a 1% increase in annual particulate matter concentration reduces the value of the average family residence by $1,140. These results highlight the vulnerability of poor rural communities to deteriorating environmental conditions.

A State Role in Supporting Groundwater Trading with Safeguards for Vulnerable Users: Findings and Next Steps

California Department of Water Resources (DWR) | May 18th, 2022

In those parts of California where groundwater pumping has long exceeded replenishment, people are striving to bring groundwater basins into sustainable conditions within

In those parts of California where groundwater pumping has long exceeded replenishment, people are striving to bring groundwater basins into sustainable conditions within 20 years, between 2040 and 2042, as the Sustainable Groundwater Management Act (SGMA) requires. In some areas, groundwater sustainability agencies (GSAs) – the local agencies tasked with sustainable groundwater management – are beginning to work with other entities and stakeholders to discuss and experiment with the idea of giving groundwater pumpers allocations – allowances to remove a certain amount of water from a groundwater basin – and allowing them to either use their allocation individually or trade allocations between specified parties. Ideally, groundwater trading could ease the economic disruption of cutting back the overall amount of water pumped from a groundwater basin; growers who have less need for pumping could sell their allocation to others willing to pay for it, helping buyers keep their operations functional while compensating sellers. But the concept of groundwater trading raises many questions: How would wetlands, streams, and other ecosystems fed by aquifers be treated in a groundwater trading program? Would operators of farms who lack the resources of larger neighbors be able to benefit from trading? How might trading affect people who depend upon a household well or communities that need reliable groundwater supplies for homes and businesses? How can GSAs work with local stakeholders to develop, implement, and oversee trading programs that help with sustainable groundwater management? There is a State interest behind all of these questions – and a clear need for a focused discussion about groundwater trading.