South Coast

Incomplete Determination for Groundwater Sustainability Plan submitted for Owens Valley Subbasin (Basin No. 6-012.01)

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

Incorporating Sea Level Change in Civil Works Programs

U.S. Army Corps of Engineers (USACE) | December 31st, 2013

Increasing Hydroclimatic Whiplash Can Amplify Wildfire Risk in a Warming Climate

Global Change Biology (Wiley) | February 7th, 2025

The catastrophic January 2025 fires were propelled by an especially extreme combination of these two recognized risk factors: (1) downslope wind gusts over 80 mph (35 m/s

The catastrophic January 2025 fires were propelled by an especially extreme combination of these two recognized risk factors: (1) downslope wind gusts over 80 mph (35 m/s) and exceptionally dry vegetation following a historically dry start to the rainy season and unusually warm antecedent temperatures driving a prolonged episode of elevated atmospheric evaporative demand. But there was also a third contributor: two consecutive anomalously wet winters (in 2022–2023 and 2023–2024), which led to abundant growth of herbaceous vegetation across CSC. This remarkable wet-to-dry sequence, therefore, set the stage for the CSC wildfire disasters to unfold by first facilitating prodigious fuel accumulation during the previous growing seasons, then subsequently drying vegetation to produce exceptional flammability unusually far into winter (when Santa Ana winds are common). Globally, climate change has increased wildfire potential primarily through greater aridity (Jain et al. 2022). In CSC, hotter summer and autumn seasons drive this aridity by increasing evaporative demand (i.e., atmospheric “thirst”), subsequently drying out vegetation. This, in conjunction with an increasingly delayed onset of the rainy season (Goss et al. 2020), may also be increasing temporal overlap between critically dry vegetation and Santa Ana winds (Swain 2021). As the events of January 2025 vividly illustrate, however, transitions from anomalously wet to anomalously dry conditions may further amplify these risks by exacerbating fuel accumulation and desiccation cycles. Indeed, in fire regimes (including CSC) where fire occurrence varies strongly with inter-annual variations in biomass (Swetnam et al. 2016), increased hydroclimate volatility is causally linked to increased wildfire activity.

Increasing threat of coastal groundwater hazards from sea-level rise in California

Nature Portfolio (Springer Nature) | August 17th, 2020

Projected sea-level rise will raise coastal water tables, resulting in groundwater hazards that threaten shallow infrastructure and coastal ecosystem resilience. Here we

Projected sea-level rise will raise coastal water tables, resulting in groundwater hazards that threaten shallow infrastructure and coastal ecosystem resilience. Here we model a range of sea-level rise scenarios to assess the responses of water tables across the diverse topography and climates of the California coast. With 1 m of sea-level rise, areas flooded from below are predicted to expand ~50–130 m inland, and low-lying coastal communities such as those around San Francisco Bay are most at risk. Coastal topography is a controlling factor; long-term rising water tables will intercept low-elevation drainage features, allowing for groundwater discharge that damps the extent of shoaling in ~70% (68.9–82.2%) of California’s coastal water tables. Ignoring these topography-limited responses increases flooded-area forecasts by ~20% and substantially underestimates saltwater intrusion. All scenarios estimate that areas with shallow coastal water tables will shrink as they are inundated by overland flooding or are topographically limited from rising inland.

Increasing water cycle extremes in California and in relation to ENSO cycle under global warming

Nature Portfolio (Springer Nature) | October 21st, 2015

Since the winter of 2013–2014, California has experienced its most severe drought in recorded history, causing statewide water stress, severe economic loss and

Since the winter of 2013–2014, California has experienced its most severe drought in recorded history, causing statewide water stress, severe economic loss and an extraordinary increase in wildfires. Identifying the effects of global warming on regional water cycle extremes, such as the ongoing drought in California, remains a challenge. Here we analyse large-ensemble and multi-model simulations that project the future of water cycle extremes in California as well as to understand those associations that pertain to changing climate oscillations under global warming. Both intense drought and excessive flooding are projected to increase by at least 50% towards the end of the twenty-first century; this projected increase in water cycle extremes is associated with a strengthened relation to El Niño and the Southern Oscillation (ENSO)—in particular, extreme El Niño and La Niña events that modulate California’s climate not only through its warm and cold phases but also its precursor patterns.

Information Needs for Water Markets: Fair and Effective Water Markets Require Adequate Measurement and Reporting of Diversion and Use

University of California, Berkeley (UC Berkeley) | November 14th, 2024

Inland Empire Interceptor Appraisal Analysis

U.S. Bureau of Reclamation (USBR) | September 16th, 2013

The Santa Ana Watershed Project Authority (SAWPA) is a joint powers authority comprised of five member water districts that serve the vast majority of the Santa Ana Water

The Santa Ana Watershed Project Authority (SAWPA) is a joint powers authority comprised of five member water districts that serve the vast majority of the Santa Ana Watershed. The area served by SAWPA is located within Orange, Riverside and San Bernardino Counties of California, bounded by the Pacific Ocean on the west, the San Bernardino Mountains to the north, and the San Jacinto Mountains to the east. The five SAWPA Member Agencies are: • Eastern Municipal Water District (EMWD), • Western Municipal Water District (WMWD), • Inland Empire Utilities Agency (IEUA), • San Bernardino Valley Municipal Water District (SBVMWD), and • Orange County Water District (OCWD). These five agencies serve most of the Santa Ana Watershed. Population within the watershed has increased significantly in recent years, and this urban growth has put enormous pressure on the regional water supply, water quality and environmental/recreation resources. SAWPA’s mission is to plan and build facilities to protect water quality and enhance the water supply within the Santa Ana River Watershed. This mission includes the goal of achieving a salt balance in the upper Santa Ana Watershed. SAWPA developed the Inland Empire Brine Line (Brine Line), which was formerly known as the Santa Ana Regional Interceptor (SARI), for the purpose of exporting salt from the Santa Ana Watershed. Exportation of salt prevents its accumulation in the watershed and protects the quality of the potable water supply. The future of the potable water supply will continue to be dependent upon an economical means of collection, treatment and disposal of brine. The Brine Line collects and disposes of brine flow from the Santa Ana Watershed and is critical to SAWPA’s mission success. The Brine Line includes approximately 72 miles of pipeline in multiple branches which converge in the vicinity of Prado Dam near the City of Corona. It has a planned capacity of approximately 32.5 million gallons per day (MGD) and was planned for collection and exportation of approximately 271,000 tons of salt per year from the upper Santa Ana Watershed, east of the Santa Ana Mountains. Currently (2010 & 2011), average system flows are approximately 11.7 MGD and over 75,000 tons of salt are exported per year. An additional 21 miles of pipeline convey the combined flows to Orange County Sanitation District (OCSD) facilities for treatment and disposal by discharge to the Pacific Ocean. This pipeline has a nominal capacity of 30 MGD. The planned capacity of the Brine Line system (32.5 MGD) exceeds the hydraulic capacity of the pipeline from the Brine Line convergence near Prado Dam to the OCSD facilities. Furthermore, the present agreement between SAWPA and OCSD allows Brine Line flows to the OCSD system up to only 17.0 MGD, with a contractual right to purchase up to 30.0 MGD capacity.

Inorganic, isotopic, and organic composition of high-chloride water from wells in a coastal southern California aquifer

Applied Geochemistry (Elsevier) | August 1st, 2005

Chloride concentrations were as high as 230 mg/L in water from the surface discharge of long-screened production wells in Pleasant Valley, Calif., about 100 km NW of Lo

Chloride concentrations were as high as 230 mg/L in water from the surface discharge of long-screened production wells in Pleasant Valley, Calif., about 100 km NW of Los Angeles. Wells with the higher Cl− concentrations were near faults that bound the valley. Depending on well construction, high-Cl−water from different sources may enter a well at different depths. For example, Cl−concentration in the upper part of some wells completed in overlying aquifers influenced by irrigation return were as high as 220 mg/L, and Cl− concentrations in water sampled within wells at depths greater than 450 m were as high as 500 mg/L. These high-Cl− waters mix within the well during pumping and produce the water sampled at the surface discharge. Changes in the major ion, minor ion, trace element, and δ34S and δ13C isotopic composition of water in wells with depth were consistent with changes resulting from SO4 reduction, precipitation of calcite, and cation exchange. The chemical and isotopic composition of high-Cl− water from deep wells trends towards the composition of oil-field production water from the study area. Chloride concentrations in oil-field production water present at depths 150 m beneath freshwater aquifers were 2200 mg/L, and Cl− concentrations in underlying marine rock were as high as 4400 mg/L. High-Cl− concentrations in water from deeper parts of wells were associated with dissolved organic C composed primarily of hydrophobic neutral compounds believed to be similar to those associated with petroleum in underlying deposits. These compounds would not be apparent using traditional sampling techniques and would not be detected using analytical methods intended to measure contamination.

Insights into estuary habitat loss in the western United States using a new method for mapping maximum extent of tidal wetlands

PLOS | August 14th, 2019

Effective conservation and restoration of estuarine wetlands require accurate maps of their historical and current extent, as well as estimated losses of these va

Effective conservation and restoration of estuarine wetlands require accurate maps of their historical and current extent, as well as estimated losses of these valued habitats. Existing coast-wide tidal wetland mapping does not explicitly map historical tidal wetlands that are now disconnected from the tides, which represent restoration opportunities; nor does it use water level models or high-resolution elevation data (e.g. lidar) to accurately identify current tidal wetlands. To better inform estuarine conservation and restoration, we generated new maps of current and historical tidal wetlands for the entire contiguous U.S. West Coast (Washington, Oregon, and California). The new maps are based on an Elevation-Based Estuary Extent Model (EBEEM) that combines lidar digital elevation models (DEMs) and water level models to establish the maximum historical extent of tidal wetlands, representing a major step forward in mapping accuracy for restoration planning and analysis of wetland loss. Building from this new base, we also developed an indirect method for mapping tidal wetland losses, and created maps of these losses for 55 estuaries on the West Coast (representing about 97% of historical West Coast vegetated tidal wetland area). Based on these new maps, we estimated that total historical estuary area for the West Coast is approximately 735,000 hectares (including vegetated and nonvegetated areas), and that about 85% of vegetated tidal wetlands have been lost from West Coast estuaries. Losses were highest for major river deltas. The new maps will help interested groups improve action plans for estuarine wetland habitat restoration and conservation, and will also provide a better baseline for understanding and predicting future changes with projected sea level rise.

Integrated Water Resources Plan 2015 Update

Metropolitan Water District of Southern California (MWD) | January 1st, 2016

In California water, uncertainty comes with the territory. Being unprepared for tomorrow, however, is simply not an option. The Metropolitan Water District of Southern C

In California water, uncertainty comes with the territory. Being unprepared for tomorrow, however, is simply not an option. The Metropolitan Water District of Southern California prepares for tomorrow with an evolving long-term water strategy known as its Integrated Water Resources Plan, or IRP. The inaugural IRP was adopted in 1996, with updates in 2004 and 2010. The 2015 IRP Update continues the tradition of assessing and adapting to changing conditions facing Southern California. The fundamental goal of the IRP is for Southern California to have as reliable a water system for tomorrow as the region has enjoyed for decades, regardless of the challenges that emerge along the way. Metropolitan plans to meet this goal through an adaptive management strategy that is the cornerstone of the 2015 IRP Update. Metropolitan was authorized by the California Legislature in 1928 to advance a regional approach to water supply in Southern California. Metropolitan’s initial mission was to construct the 242-mile Colorado River Aqueduct to its service area on the Southern California coastal plain. Metropolitan’s service area had an assessed property valuation of approximately $2 billion at the time. Now Metropolitan serves a six-county service area with a property valuation of approximately $2 trillion. Metropolitan imports supplies from both the Colorado River and Northern California via the State Water Project while investing in a variety of storage, local supply and conservation initiatives. Metropolitan has a long record of promoting alternatives to imported water supplies, dating back to the 1980s. With the IRP, that process became more formalized as a long-term strategy and official policy. Metropolitan has steadily diversified the future water portfolio for Southern California with each revision to the IRP. This update is no exception. Investments to maintain the reliability of imported supplies are complemented by an expansion of local supply development along with a reduction in demand through a variety of conservation and water-use efficiency initiatives. The necessary suite of actions evolves over time based on the water conditions of tomorrow. Updating the IRP creates a new baseline for managing into the future.