Snow-eater heat waves of the western United States

American Association for the Advancement of Science (AAAS) | August 5th, 2026

Abrupt snowmelt, triggered by rain-on-snow events or “snow-eater heat waves,” can cause flooding, initiate or accelerate snow drought, and affect water availability.

Abrupt snowmelt, triggered by rain-on-snow events or “snow-eater heat waves,” can cause flooding, initiate or accelerate snow drought, and affect water availability. However, the characteristics (e.g., area, duration, and frequency), impacts, and trends of snow-eater heat waves have received little attention. To address this gap, we developed a method to identify snow-eater heat waves and estimate their melt potential using 20th Century Reanalysis version 3 air temperature data, the TempestExtremes algorithm, and an operational snowmelt model (SNOW-17) across 1850–2015. Melt season snow-eater heat waves typically last 3 to 5 days, with three to five events, doubling snowmelt rates. Seven of 11 spring superfloods are shown to coincide with snow-eater heat waves. Since the 1850s, snow-eater heat waves have increased in area and frequency, decreased in duration, and shifted earlier in the melt season. Incorporating snow-eater heat-wave impacts into SNOW-17 enhances extreme melt estimates, improving water management support tools.

Beyond Watershed Planning: Engaging Communities to Improve Outcomes of the Safe Clean Water Program

Los Angeles Waterkeeper (LA Waterkeeper) | August 11th, 2026

In the eight years since Los Angeles voters approved Measure W, the LA County Flood Control District has successfully launched the Safe Clean Water Program (SCWP). The pr

In the eight years since Los Angeles voters approved Measure W, the LA County Flood Control District has successfully launched the Safe Clean Water Program (SCWP). The program collects approximately $280M every year and distributes those funds to support stormwater capture projects that can reduce flooding, improve regional water quality, recharge groundwater, and provide a variety of benefits for communities and wildlife. To date, the SCWP has funded 473 projects, studies, concepts, and program activities through its regional, municipal, and district programs.  The program takes an adaptive management approach to ensure funds are invested effectively and that supported projects deliver meaningful reductions in flood risk while providing appropriate treatment of local stormwater. This approach also ensures funds are leveraged to provide the most potential benefits for every dollar spent. As part of that effort, the SCWP developed a watershed planning process in 2024 with the goal of maximizing potential benefits in each of the county’s nine watersheds.  Los Angeles Waterkeeper secured funding to conduct five community workshops to further inform the watershed planning process moving forward. The purpose of these workshops was to ensure that individuals and organizations who are well informed about the on-the-ground needs and priorities of communities throughout LA County had the opportunity to provide input to the watershed plans. LA Waterkeeper partnered with community-based organizations in each of the areas where the workshops were held to invite priority participants, although all workshops were open to the public. 

Quality of Surface Waters of the United States, 1965, Parts 7 and 8, Lower Mississippi River Basin and Western Gulf of Mexico Basins

U.S. Geological Survey (USGS) | July 15th, 1970

Quality of Surface Waters of the United States, 1965, Parts 5 and 6, Hudson Bay and Upper Mississippi River Basins and Missouri River Basin

U.S. Geological Survey (USGS) | July 15th, 1970

[caption id="attachment_38764" align="alignnone" width="533"] Screenshot[/caption]

[caption id="attachment_38764" align="alignnone" width="533"] Screenshot[/caption]

Quality of Surface Waters of the United States, 1965, Parts 3 and 4, Ohio River Basin and St. Lawrence River Basin

U.S. Geological Survey (USGS) | July 15th, 1970

Quality of Surface Waters of the United States, 1965, Parts 1 and 2, North Atlantic Slope Basins and South Atlantic Slope and Eastern Gulf of Mexico Basins

U.S. Geological Survey (USGS) | July 15th, 1970

Quality of Surface Waters of the United States, 1965, Parts 9-11, Colorado River Basin to Pacific Slope Basins in California

U.S. Geological Survey (USGS) | July 15th, 1970

Simulation of the Impacts of Spring Diversions on Streamflow in the Strawberry Creek Watershed, San Bernardino County, California, Using an Integrated Hydrological Model

U.S. Geological Survey (USGS) | July 27th, 2026

The Strawberry Creek watershed, in the San Bernardino Mountains of southern California, features a group of natural springs known as Arrowhead Springs that have been augm

The Strawberry Creek watershed, in the San Bernardino Mountains of southern California, features a group of natural springs known as Arrowhead Springs that have been augmented with diversions in the form of sub-horizontal borings and tunnels. Understanding the effects of these structures on streamflow through groundwater capture is crucial for managing surface-water resources in this watershed. In this study, we constructed the Strawberry Creek integrated hydrological model to increase this understanding. The Strawberry Creek integrated hydrological model is an integrated surface runoff and groundwater model, GSFLOW to simulate surface runoff and infiltration and groundwater flow. The model has 263 rows and 176 columns in each of its three layers. The model area includes the Strawberry Creek and four adjacent watersheds. The precipitation- runoff modeling system was calibrated using two streamflow gaging stations, and the groundwater and surface-water flow model was calibrated to the reported spring diversion discharge and a sparse number of groundwater- level measurements. The Strawberry Creek integrated hydrological model was run with and without diversions active, and simulated streamflow was compared, indicating that in the headwaters of Strawberry Creek, about 35 percent of the diversion flow was captured from base flow.

Abrupt transition to irreversible damage in the overdrafted Sacramento Valley aquifer system

National Academy of Sciences (NAS) | July 27th, 2026

Groundwater extraction can cause both reversible and irreversible ground deformation, with the latter leading to permanent land subsidence and loss of groundwater storage

Groundwater extraction can cause both reversible and irreversible ground deformation, with the latter leading to permanent land subsidence and loss of groundwater storage capacity. Satellite observations of land surface deformation reveal that large areas of the Sacramento Valley abruptly transitioned from reversible to irreversible compaction over the 2020–2022 California drought—a transition not anticipated from the groundwater monitoring network alone. Subsidence rates reaching several decimeters per year and not following groundwater levels indicate lasting damage to the aquifer system and underscore the need for more conservative groundwater management. By imaging this sharp transition at the regional scale, our analysis demonstrates the potential of space-based monitoring for early detection of groundwater overdraft and the resulting loss of aquifer storage capacity worldwide.

Assessing the Status and Drivers of Phytoplankton Blooms along the Riverine to Freshwater-Tidal Continuum in a Modified Delta

Springer Nature | August 1st, 2026

Shifts in phytoplankton communities, from beneficial taxa that fuel food webs to harmful taxa that degrade water quality, are often linked to anthropogenic modifi

Shifts in phytoplankton communities, from beneficial taxa that fuel food webs to harmful taxa that degrade water quality, are often linked to anthropogenic modifications to estuaries. We analyzed monitoring data from 2000 to 2023 in the heavily modified southern, landward portion of the Sacramento-San Joaquin Delta (California, USA) to determine the status and drivers of phytoplankton abundance and community composition along the riverine to freshwater tidal transition. Diatoms and green algae dominated the phytoplankton community, especially when chlorophyll a (chl-a) concentrations exceeded 16 µg L− 1. Common riverine diatoms (e.g., Cyclotella and Aulacoseira) dominated upstream riverine stations, while taxa associated with tidally influenced conditions (e.g., colonial cyanobacteria, cryptophytes) were more prevalent in western, freshwater tidal stations. The potentially toxigenic cyanobacterium, Microcystis, was present each summer, but was not associated with elevated chl-a or cyanotoxins (microcystins were detected in 12% of samples with a maximum concentration of 3.9 µg L− 1). A Bayesian ordinal regression showed that mean prior week water speeds below 0.18 m s− 1 and water temperatures above 22 ˚C were associated with the presence of Microcystis.Random forest modeling to assess factors associated with phytoplankton blooms (chl-a > 16 µg L− 1) found that mean prior week turbidity, inflows from the San Joaquin River, region, and mean prior week water temperature were important drivers of blooms. These modeling results emphasize the importance of hydrodynamics in controlling phytoplankton dynamics in lowland rivers and tidal deltas, offering insights for how anthropogenic impacts on flow regimes may affect the base of estuarine food webs.