Closing the gap between micro- and nano plastics science and policy

Nature Portfolio (Springer Nature) | September 25th, 2026

Grain size and sediment storage explain why postfire debris flows are absent in some mountainous landscapes

American Association for the Advancement of Science (AAAS) | September 25th, 2026

Postfire debris flow occurrence varies widely in mountainous landscapes, even under similar rainfall conditions. To understand why, we investigated two burned landscapes

Postfire debris flow occurrence varies widely in mountainous landscapes, even under similar rainfall conditions. To understand why, we investigated two burned landscapes that experienced intense postfire rainfall: one in southern California with over 100 postfire debris flows and one in northern California with no postfire debris flows. Debris flows can initiate from bed failures that are predicted to occur when Shields stress τ∗ exceeds a threshold. We characterized τ∗ at the two sites, investigated bed failure, and conducted numerical experiments to identify controlling factors. Postfire increases in clear-water runoff raised τ∗ by up to threefold, whereas postfire reductions in channel grain size raised τ∗ by two orders of magnitude. No increase in runoff was required to initiate debris flowsat the southern California site, yet debris flows were unlikely to initiate at the northern California site even for considerable increases in runoff. These results provide a mechanistic explanation for discrepancies in debris flowoccurrence in mountainous landscapes.

Delta Science Program Research Impact Report

Delta Stewardship Council (Delta Council) | September 23rd, 2026

Evaluation of Hydrogen Sulfide in Outdoor Air Environmental Contamination in the Tijuana River

U.S. Department of Health and Human Services (DHSS) | September 23rd, 2026

In May 2024, the Centers for Disease Control and Prevention (CDC)/Agency for Toxic Substances and Disease Registry (ATSDR) received a petition from members of the Califor

In May 2024, the Centers for Disease Control and Prevention (CDC)/Agency for Toxic Substances and Disease Registry (ATSDR) received a petition from members of the California congressional delegation to investigate the public health impacts of Tijuana wastewater contamination, both in the Tijuana River and in the surrounding communities of Imperial Beach, Coronado, and San Diego. The congressional delegation requested that CDC/ATSDR assess the presence of contaminants in the communities' water, soil, and air. CDC/ATSDR was also asked to investigate any potential connection between these contaminants and the reported increases in gastrointestinal illnesses and other symptoms. In July 2024, the CDC/ATSDR director responded that ATSDR would start the petition process to investigate specific environmental health concerns. ATSDR gathered air, surface water, sediment, and biota data from federal, state, local, and academic partners, determining that there were enough data to accept the petition. On January 7, 2025, the CDC/ATSDR director notified the congressional delegation that ATSDR would conduct a public health assessment of hydrogen sulfide in the air [CDC/ATSDR 2025]. ATSDR will release the findings of the public health assessment activities in two reports. This is the first, focusing on potential exposures to contaminants in air in the Tijuana River Valley. A second report will address other potential exposure pathways, like surface water, sediment, and soil. In this health consultation, ATSDR evaluated exposures to air contaminants via outdoor air in the Tijuana River Valley following the agency's public health assessment (PHA) process, as summarized in Appendix A, and detailed in ATSDR's Explanation of ATSDR's PHA Process [ATSDR 2022].

An eastward-propagating coupled mode amplifying the early growth of extreme El Niño events

American Association for the Advancement of Science (AAAS) | September 23rd, 2026

Extreme El Niño events are among the most consequential climate phenomena, yet their early prediction remains challenging. Here, by analyzing the 1982/1983, 1997/1998, a

Extreme El Niño events are among the most consequential climate phenomena, yet their early prediction remains challenging. Here, by analyzing the 1982/1983, 1997/1998, and 2015/2016 events together with a large ensemble of climate model simulations, we identify an unusually early and reproducible ocean-atmosphere precursor to extreme El Niño: a slow, eastward-propagating coupled mode that develops in the western-central equatorial Pacific during boreal winter and spring. This mode features warm sea surface temperature anomalies coupled with sustained westerly wind anomalies. These westerly wind anomalies drive the equatorward transport of warm water, rapidly increasing equatorial ocean heat content and priming extreme El Niño growth in the following summer and fall. Ensemble hindcasts further reveal that East Asian cold surges and the North Pacific Oscillation can stochastically excite this equatorial mode, enabling skillful forecasts of extreme events as early as February and helping to overcome the spring predictability barrier.

Bulletin 161-2026 Annual Water Supply and Demand Assessment Summary Report

California Department of Water Resources (DWR) | September 21st, 2026

This report summarizes the Department of Water Resources’ (DWR’s) review of Urban Water Suppliers’ Annual Water Shortage Assessment Reports (Annual Shortage Reports

This report summarizes the Department of Water Resources’ (DWR’s) review of Urban Water Suppliers’ Annual Water Shortage Assessment Reports (Annual Shortage Reports) for the State Water Resources Control Board (State Water Board). As directed by the California Water Code (CWC) Section 10644(c)(1)(B), this summary report includes water shortage information at the supplier level, as well as regional and statewide analyses of water supply conditions.

Mass balance of the Greenland and Antarctic ice sheets from the 1970s to 2023

Nature Portfolio (Springer Nature) | September 16th, 2026

The Greenland and Antarctic ice sheets are major drivers of global mean sea level rise and are predicted to continue to do so in the future. However, they also re

The Greenland and Antarctic ice sheets are major drivers of global mean sea level rise and are predicted to continue to do so in the future. However, they also represent the largest source of uncertainty in projections of future sea level rise making robust estimates of observed ice sheet mass changes critical. Here, we compare and combine 42 independent estimates of ice sheet mass balance derived from satellite observations of temporal changes in ice sheet flow, volume, and gravitational attraction to determine the ice sheet mass balance from 1972 (Greenland) and 1979 (Antarctica) until 2023. We then use regional climate models to partition the total mass balance into contributions associated with surface mass balance and ice dynamical imbalance. The ice sheets lost 11,309 ± 565 billion tonnes of ice between 1979 and 2023, with glacier dynamical imbalance driving 84% of the ice loss and surface mass balance the remainder. This dataset can be used to track the contribution of the ice sheets to sea level rise and constrain projections of future sea level rise.

California to spend billions on ‘visionary’ plan to boost fish habitat. But skeptics question whether effort to save San Francisco Bay delta region will work without allocating more water for nature

American Association for the Advancement of Science (AAAS) | September 15th, 2026

California’s San Francisco Bay delta region is the site of some of the country’s fiercest water wars, rivaling the drought-stricken Colorado River Basin. The delta, w

California’s San Francisco Bay delta region is the site of some of the country’s fiercest water wars, rivaling the drought-stricken Colorado River Basin. The delta, which lies between San Francisco and Sacramento, California, is the last refuge of seven endangered fish species and the central hub for diverting water to farms and cities, and there has long been too little to go around. Now, the state has reached the final stages of overhauling water policy for the entire delta for the first time in 30 years, and many stakeholders are unhappy.

Large Seasonal Variation in Microplastic Concentration from the Truckee River, United States

American Chemical Society (ACS) | September 15th, 2026

Microplastics (MPs) are ubiquitous in riverine environments worldwide, but arid river systems, characterized by large seasonal variations in discharge, remain understudie

Microplastics (MPs) are ubiquitous in riverine environments worldwide, but arid river systems, characterized by large seasonal variations in discharge, remain understudied. Using a peristaltic pump, we collected samples for MP surface concentration analysis along the Truckee River in the western United States. Samples were collected using a 100 μm filter during fall 2022 and spring 2023 across 6 and 8 sites, respectively. The samples were analyzed with microscope-enabled Fourier Transform Infrared spectroscopy, and the resulting MP concentrations were compared to land use and river discharge. MP concentrations were higher in spring (mean 3.7 MP/L) than in fall (mean 0.4 MP/L), coinciding with an increase in river discharge. Statistical analyses revealed significant seasonal differences in polymer composition because of increased concentrations of poly(ethylene terephthalate), polyethylene, and rubber in spring. These patterns likely reflect increased spring discharge mobilizing MPs from the surrounding landscape and riverbed sediments. These findings underscore the complexity of MP sources and transport and highlight the importance of seasonal sampling across discharge and land-use types. Additionally, polypropylene, poly(ethylene terephthalate), and polyethylene were the dominant polymer types overall, demonstrating that reducing single-use plastic in the Truckee River Basin is important for protecting the river’s water quality.

Widespread drought-driven declines in streamflows and water quality in the Upper Colorado River Basin during 1998-2022

Nature Portfolio (Springer Nature) | September 14th, 2026

The cascading effects of meteorological droughts on river flows and water quality in mountainous regions are poorly understood. Using a data-driven framework, we studied

The cascading effects of meteorological droughts on river flows and water quality in mountainous regions are poorly understood. Using a data-driven framework, we studied drought impacts on streamflow, water temperature (WT), specific conductance (SC) in the Upper Colorado River Basin (1998-2022). Severe meteorological droughts in 2001-2002, 2012, 2018, 2020-2021 reduced annual streamflows by 15%, increased WT by 9% and SC by 5% relative to normal adjacent years. Declines were greatest in spring and summer, with reduced peak flows. Streamflow and SC recovered until 2018, after which successive droughts prolonged impacts, whereas WT effects were transient. Catchments with higher freshwater withdrawals, deciduous forest cover, air temperatures, residence times, finer soils had greater streamflow declines, while higher subsurface flows and infiltration enabled resilience. WT increases were associated with higher elevation, slopes, precipitation and lower agriculture, shrub cover. Open water and reservoirs mitigated SC increases. Thus, catchment attributes influence drought vulnerability in mountainous regions.