Zotero Items

Title	Date	Authors	Abstract	URL
Can we maximize snow storage through fire-resilient forest treatments? Insights from experimental forest treatments in the Eastern Cascades, WA, USA	2026-3-3	Lumbrazo et al.	Forest treatments such as prescribed burns, mastication, and thinning are widely implemented across the western USA to reduce fuels and enhance wildfire resilience. These practices also influence snow accumulation and melt, which, in turn, affect snow storage and duration. Since many regions depend on seasonal snow for water resources, it is essential that forest management practices preserve or even enhance snow storage as a buffer against the impacts of climate change. To test the hypothesis that thinning and canopy gap creation can maximize snow storage, particularly on north-facing slopes, experimental forest treatments representing a range of thinning intensities were implemented on Cle Elum Ridge in the headwaters of the Yakima River Basin, Washington, USA. Ground-based snow observations, combined with pre-treatment (2021) and post-treatment (2023) snow-on lidar, show that canopy thinning increased snow depth and storage by 30% on north-facing slopes and by 16% on south-facing slopes. Snow depth was positively related to canopy openness, as measured by sky view fraction and canopy edge metrics, with stronger effects on north-facing slopes. In contrast, there was no clear relationship between snow depth and degree of thinning as measured by forest basal area, a common forestry metric used to plan treatment prescriptions. Using canopy edge metrics and sky view fraction relationships, we estimated the hydrologic benefit of thinning during 2023 at 12.3 acre-feet of water storage per 100 acres of north-facing forest and 5.1 acre-feet on south-facing slopes. These findings highlight the potential to incorporate hydrologic resilience as a co-benefit when planning fuel reduction strategies.	https://www.frontiersin.org/articles/10.3389/ffgc.2025.1707812/full
The Role of Groundwater in Contributing to Surface Water Salinization in the Upper Colorado River Basin	2026-04-28	Miller et al.	Abstract Freshwater salinization affects the availability of water for human use and ecosystem needs worldwide. It has been estimated that total dissolved solids (TDS) in the Colorado River Basin cause $350 million/year in damages and substantial resources are devoted to reducing TDS loading to streams. This study describes the development and application of coupled watershed models that enable TDS source tracking through the subsurface and across the landscape at a seasonal timestep for 35 years in the Upper Colorado River Basin. Results indicate that, on average, 75% of TDS loading to streams originates as baseflow, and 50% of loading is lagged in delivery by longer than one season. Snowmelt was identified as a dominant process controlling the transport of lagged TDS to streams. This approach informs when and where TDS mitigation efforts may be effective in a watershed that serves as a critical water supply for the southwestern United States. , Plain Language Summary The amount of salt in surface waters has increased across the world and is expected to increase in the future. High levels of salt can limit human use of water and can have negative effects on aquatic life. It has been estimated that salt in the Colorado River Basin causes $350 million/year in damages via corrosion of pipes and reduction of agricultural output. Understanding where salt that ends up in streams and rivers is coming from in a watershed, and how it gets transported to streams, is important for identifying approaches to mitigate salt impacts to humans and aquatic ecosystems. We estimate that 75% of salt loading to streams in the Upper Colorado River Basin comes from groundwater and that half of the salt loading to streams takes longer than one season to move from the landscape to streams. Further, we demonstrate that snowmelt is an important process for moving salt stored in the watershed to streams. This approach can be applied to identify when and where salt mitigation efforts may be effective in a watershed that serves as a critical water supply for the southwestern United States. , Key Points Baseflow contributed 75% of total dissolved solids loading to streams, with 50% of load lagged in delivery by longer than one season Snowmelt is a dominant process transporting total dissolved solids in lagged baseflow from the landscape to streams Models estimate when, where, and from what source total dissolved solids loads are being delivered to the basin outlet	https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025GL118834
Impact of Groundwater Management on Drought Responses in the Southwest	01/2026	Tadych et al.	Abstract Long-term groundwater declines driven by human consumption are occurring around the world; however, the extent these trends are accelerated by drought conditions is less clear. In arid locations with limited reliance on surface water supplies, are groundwater declines still sensitive to drought conditions, or are trends driven solely by human consumption? Here, we use Arizona in the southwestern United States to explore drought response in a heavily groundwater-dependent arid system. We use a series of statewide, regional, and local case studies to perform a qualitative analysis on well data from 2000 to 2022 to illustrate how spatial variability in land use, surface water access, groundwater management, and policy impact groundwater. Areas with major characteristics are identified, and linear regression is performed on groundwater levels for each area over time. Across the state, groundwater levels have been declining for more than 50 years and persistent groundwater declines are noted in most large regions. Severe drought can further accelerate depletions beyond the long-term trends, especially in groundwater-dominated areas without pumping regulations. However, this is not the case everywhere. In major metropolitan areas, and in agriculturally dominated locations with direct access to regional surface water supplies (Colorado River), drought response is significantly dampened. In some locations, we show no added drawdown during drought or even a slight recovery. Overall, our results show that long-term groundwater declines can be exacerbated during drought periods, but spatial differences in our case studies highlight the importance of diverse water sources and local management decisions. Instances of groundwater recovery highlight the potential for sustainable groundwater management in water limited areas. Significance Statement Groundwater levels are declining in many parts of the world. In many cases, declining trends are driven by sustained over pumping, and it is unclear how big an impact drought has relative to these human effects. Here, we perform a qualitative case study analysis to explore the impact of meteorological drought on groundwater levels in Arizona to better understand whether weather conditions are a major factor in accelerating groundwater declines. Arizona provides an excellent testing ground for this research due to its arid climate and groundwater dependence, as well as the spatial variability in groundwater governance and water availability. We use case studies with multiple major characteristics to illustrate the impact that land use, surface water access, groundwater management, and policy can have on groundwater outcomes. Our results show that drought does not always induce groundwater declines. Local groundwater policy and the diversity of the water supply portfolio can have a big impact on outcomes. Our findings are relevant for other arid locations struggling with groundwater sustainability and illustrate that there are multiple pathways to improving groundwater resilience.	https://journals.ametsoc.org/view/journals/wcas/18/1/WCAS-D-24-0156.1.xml
Surface Quantitative Precipitation Estimates (SQUIRE) of Snow Water Equivalent from the Surface Atmospheric Integrated Field Laboratory	01/2026	Jackson et al.	Abstract The upper Colorado River basin is the primary source of water for 40 million people. With declining snowpack in the basin, forecasting hydrological budgets in the Southwest United States is more important than ever. However, due in part, to a lack of reliable observations of precipitation in complex terrain, hydrological models struggle to assess and forecast snowpack snow water equivalent (SWE) in the upper Colorado River basin (UCRB). Therefore, the need for more reliable SWE forecasts in the UCRB motivated the U.S. Department of Energy Atmospheric Radiation Measurement Facility’s Surface Atmospheric Integrated Field Laboratory (SAIL) that occurred from June 2021 to June 2023. During SAIL, the X-band precipitation radar from Colorado State University conducted volume scans sampling the precipitation properties over the UCRB. The ARM facility developed a gridded Surface Quantitative Precipitation Estimates (SQUIRE) product from the radar observations. To do this, various daily SWE estimates from radar using the radar reflectivity factor Z e and specific differential phase K dp were compared against ground-based precipitation gauges. SWE in precipitation calculated from Wolfe and Snider’s S – Z e estimator was in best agreement with the rain gauges for the days when SWE < 12 mm. For days with SWE > 12 mm, the WSR-88D Intermountain West relationship had the best agreement with the precipitation gauges. Airborne snow depth observations show that SQUIRE captures regions of orographic enhancement in the mountains to the west and northwest of the SAIL study area, indicating that the scientific community should focus on understanding and ultimately simulating orographic atmospheric precipitation processes to improve UCRB snowpack SWE assessment and forecasting. Significance Statement This paper looks at snowfall estimates from data collected during a field experiment in the upper Colorado River basin, a critical source of water for 40 million people in the United States. Here, our typical radars do not detect precipitation in this crucial region, so we detail the methods we used to estimate snowfall rates from these new data that will help scientists better predict the amount of water that will be available for people living in the Southwest United States.	https://journals.ametsoc.org/view/journals/atot/43/1/JTECH-D-25-0023.1.xml
Why Communicating Minimum Drawdown Elevations for Lake Powell and Lake Mead Can Mitigate Risks of Volatile Colorado River Flow.	2026	Fager et al.	Summary - Colorado River precipitation and flows have been volatile. There is consensus across Reclamation’s hydrologic ensembles that volatility will continue, including annual drops of 6 million acre-feet of natural flow above Lake Powell. At historically low Lake Powell and Lake Mead elevations, a 1-year drop can draw down reservoirs to catastrophic levels where the system can no longer fulfill its Congressionally mandated purposes: deliver water, generate hydropower, protect native fish, or sustain infrastructure. In this post we suggest four reservoir strategies to reduce all those risks: (1) Identify Catastrophic Elevations where we lose the ability to operate the system for one or more intended purposes, (2) Communicate Minimum Drawdown Elevations as storage buffers to mitigate catastrophic risks, (3) Sustain minimum drawdown elevations, such as by adapting releases to monitored changes in physical reservoir inflow and reservoir evaporation, (4) Increase the frequency of decisions to respond sooner and more flexibly to volatile flow. Water held in Lake Powell and Lake Mead between their minimum drawdown and catastrophic elevations generates continuing benefits for hydropower, native fish, infrastructure, and capacity to deliver water, whereas if released, buffer water can only be consumed once by downstream users. Moving to monthly or weekly decisions provides earlier, smaller, smoother, and more predictable changes in reservoir releases compared to delayed, larger, and more sudden shocks from the current practice of setting annual releases in Fall and possibly updating them in the Spring. We do not recommend specific minimum drawdown elevations. Rather, we emphasize the importance to communicate methods that maintain public trust that the Colorado River system will not collapse.	https://digitalcommons.usu.edu/water_rep/688/
How a 3 to 5-Year Experimental Lake Powell and Lake Mead Release Program Tied to Reservoir Inflows can be a Win for Adaptive Risk Management	2026	Fager et al.	Lake Powell and Lake Mead are at risk of drawdown to their minimum power and dead pools in the next few years because current and proposed shortage and release operations tied to reservoir storage cannot keep pace with the numerous scenarios of more volatile and declining flows within Reclamation’s hydrology. Reclamation’s scenarios also have longer-lasting periods of low flow. One experimental program to reduce risk can instead adapt reservoir releases to monitored changes in physical reservoir inflow and reservoir evaporation. First, stabilize reservoir storage by temporarily setting reservoir release to the physical reservoir inflow minus evaporation (the available water). Second, continue to stabilize storage by changing releases to match changes in physical reservoir inflow and evaporation. Third, build storage by decreasing releases from the release needed to stabilize reservoir storage. An experimental program has additional wins such as it can begin immediately or at any target reservoir elevation without the need for new agreements. A program can also stabilize and build reservoir storage even when low flows persist. Users who hold back some of their share of reservoir releases can customize and adapt strategies to manage their future risks of water shortages. An experimental risk management program can also encourage a new mindset of holding some of the physical reservoir inflow to increase future operational flexibility when flows may be lower. We share links to further explore some of these new risk communication and adaptive management tools.	https://digitalcommons.usu.edu/cee_facpub/3828/
Gorsuch’s Dissent and the Current State of Navajo Water Rights Claims	2026	Clark		https://dc.law.utah.edu/ulr/vol2026/iss1/4
Warming and snow loss increase reliance on old groundwater in a Colorado River headwater	05/2026	Siirila-Woodburn et al.	Abstract Atmospheric warming is reducing snowpack, with uncertain effects on mountainous streamflow, a crucial water resource. Despite limited historical observations of groundwater–streamflow interactions above 2,500 m, new measurements in the Upper Colorado River headwaters indicate declining groundwater storage that is dated decades to millennia old. Here we use integrated hydrologic modelling spanning water years 2015–2021 to determine whether the loss of old-age groundwater buffers streamflow during low-snow years and whether that loss is exacerbated with warming. Results show that old-groundwater contributions to streams remain relatively steady through time, unlike the more variable contributions from young groundwater. Numerical experiments of increased surface air temperatures (+2.5 °C and +4 °C) increase rain–snow fractions and evapotranspiration and decrease runoff ratio by 2–3% per degree Celsius increase. As streamflow declines with warming, the age of groundwater supporting it gets older, in part owing to intermediate-aged (1–3 year) groundwater declining twice as fast. Simulations show that water table depths at higher elevations (>3,700 m) decline disproportionately and fail to recover even during wet years. These findings suggest altered groundwater–streamflow interactions with warming and snow loss, with implications for water resources.	https://www.nature.com/articles/s41561-026-01945-y
Integrating mark-recapture, catch, and expert habitat assessments to quantify recent increases in humpback chub abundance over a 200 km long river segment of the Colorado River in western Grand Canyon	2026-01-01	Dzul et al.	Humpback chub, Gila cypha, were historically distributed throughout large portions of the Colorado River basin and were federally listed in 1967. In the Grand Canyon segment of the Colorado River, located below Glen Canyon Dam, chub abundances continued to decline through the early 2000s. Recently, catch has increased substantially, especially in the western Grand Canyon. Here, we integrate mark-recapture and catch data of subadult and adult humpback chub, with expert assessments of habitat suitability and an underlying model of spatial autocorrelation, to estimate abundance in western Grand Canyon from 2010 to 2024, a time of rapid population increase and expansion. Our model suggests that adult abundance grew ∼160 fold during this 15-year period, with a median adult population abundance of 70 000 (40 000–200 000; 95% credible interval) in 2024. Our approach identifies years with high population growth and indicates that the spatial distribution has changed over time. We test the sensitivity of our results to movement into sampling reaches during sampling with baited hoop nets. Despite rapid population growth, the resilience of humpback chub in western Grand Canyon is unknown.	https://cdnsciencepub.com/doi/10.1139/cjfas-2025-0169
Making Waves: The Effects of Whitewater Parks on Fish Passage in Colorado	02/2026	Richer et al.	Instream structures have fragmented riverine habitats throughout much of the world, including the Western USA. Whitewater parks (WWPs) are relatively new instream structures designed to create hydraulic waves for recreational boating and surfing by constricting flows into a steep chute or drop. The altered hydraulics at these structures can adversely affect fish passage, particularly in locations where fish species are not adapted to the new hydraulic regime. This study evaluates the effects of WWPs on fish passage at two sites in Colorado by comparing water velocity and depth to fish passage criteria for three size classes (juvenile, average adult, and large adult) and species of interest (Brown Trout, Colorado Sculpin, and Flannelmouth Sucker). The before-after study design utilized two-dimensional hydrodynamic modeling, spatial analysis, and logistic regression to evaluate fish passage over a range of flows. WWP construction altered channel hydraulics, including elevated and more variable velocity, and decreased depth. Complete barriers to upstream passage were created for certain combinations of species, size class, and flows due to velocity and/or depth limitations. Passable pathways and passage probability decreased for all species following WWP construction, with Brown Trout maintaining the highest proportion of passable paths (23%) when averaged across flows and structure, followed by Colorado Sculpin (15%) and Flannelmouth Sucker (2%). These results indicate that WWP construction decreased fish passage at these sites and highlight the importance of using site-specific criteria and permitting requirements to ensure that adequate safeguards for fish passage are incorporated into the design of WWP structures.	https://onlinelibrary.wiley.com/doi/10.1002/rra.70069
Scale- and Seasonal-Dependent Sensitivity of Hydrologic Projections in the Colorado River Basin to Different Downscaling Methods	05/2026	Currier et al.	Abstract This study created future streamflow projections using dynamically downscaled precipitation and temperature projections from the Intermediate Complexity Atmospheric Research (ICAR) model and the Variable Infiltration Capacity (VIC) model. These more physically realistic projections were compared with VIC simulations based on the widely utilized localized constructed analog (LOCA) statistical downscaling method to evaluate how downscaling choices influence water supply estimates. ICAR’s annual streamflow change at Lees Ferry, Arizona, was higher than LOCA in the ensemble mean due to equal influences from precipitation and temperature. However, annual streamflow changes at Lees Ferry were not significantly different between downscaling methods despite significant differences in precipitation and temperature as there was still a substantial spread and there were no systematic differences between downscaling methods across Earth system models. Similar streamflow projections were the result of different seasonal and spatial patterns. For example, while ICAR projected less cool-season precipitation than LOCA at high elevations (>3000 m), summer precipitation projections, which are often characterized as more uncertain, differed substantially between downscaling methods and increased ICAR’s streamflow projections relative to LOCA. Furthermore, downscaling decisions were more likely to affect streamflow projections at the local scale rather than the regional scale as 25%–32% of the smaller catchments within the upper basin showed significant differences between downscaling methods in annual streamflow changes. Finally, this study considers the uncertainty and confidence in the process representation of precipitation and temperature, emphasizing how spatial and seasonal differences in these variables—and the ways their underlying processes are represented—directly influence streamflow projections.	https://journals.ametsoc.org/view/journals/hydr/27/5/JHM-D-25-0155.1.xml
The Old Flows with the New: Interstate Compacts as a Modern Mechanism for Water Governance on the Colorado River	Spring 2026	Alberts	When first researched in the summer of 2024, this article soughttoexaminethetheoreticalinabilityofColoradoRiverBasinStatesto negotiateanewwaterdealinthewakeoftheFederalGovernment’sproposed intervention in 2023. Since pre-publication, a new administration has taken aggressiveholdoffederalagencies,theBasinStateshavestillnotreachedan agreementtodivideColoradoRiverwater,andas2025drawstoaclose,the stateofColoradoispossiblyfacingitsdriestwinterinhistory.Thisarticleseeks todoonething:reintroduceinterstatecompactingasatooltoreducefrictionin decision making between states over Colorado River resources. Through a survey of the current physical reality of the Colorado River, a catalogue of examplesdealingwithinterstatecompacting,andadraftproposalforanew system, this article hopes to chart a course forward in these stressed and uncomfortabletimesfortheColoradoRiverBasin.	https://digitalcommons.du.edu/wlr/vol29/iss1/5/
Perspectives on United States–Mexico Cooperation on the Colorado River	2026-01-02	Gerlak et al.		https://www.tandfonline.com/doi/full/10.1080/00139157.2025.2575762
Expanding the Good Samaritan Program: Cleaning Up the Colorado River, One Mine at a Time	2026-01-01	Carlson	The headwaters of the Colorado River Basin supply nearly 90% of the river’s flow and are among the most hydrologically sensitive areas in the U.S. During the nineteenth and early twentieth centuries, westward expansion and the allure of gold and other valuable minerals drove thousands of miners into the basin. When the mining boom ended, the mines were left behind. Today, thousands of abandoned hardrock mine sites continue to leach acidity and heavy metals into streams, leaving a lasting impact on water quality. For decades, strict environmental liability laws made cleanup nearly impossible, creating a chilling effect that discouraged even well‑intentioned remediation. Congress attempted to change this dynamic with the Good Samaritan Remediation of Abandoned Hardrock Mines Act of 2024, which launched a pilot program limiting liability for third parties who take on cleanup projects. This Comment argues that while the Act is a step forward, Congress should (1) improve funding opportunities for abandoned mine remediation projects by establishing a hardrock royalty, and (2) make the Good Samaritan Program permanent rather than allowing it to sunset after the pilot period. Additionally, the U.S. Environmental Protection Agency should issue guidance prioritizing projects in headwater areas, those with potential for responsible critical mineral and rare earth element reprocessing, and those that meaningfully engage with local communities. Expanding the program in these ways would accelerate cleanup, protect water resources, and ensure reclamation delivers ecological, economic, and social benefits across the basin.	https://scholarship.law.uwyo.edu/wlr/vol26/iss2/5
Climate change impacts and adaptation in the agricultural sector of the Colorado River Basin: a hydro-economic analysis	2026-06-09	Crespo et al.		https://www.elgaronline.com/view/book/9781035344970/chapter12.xml
Continuous and high-resolution longitudinal profiles of the water surface and riverbed elevation for 282 miles of the Colorado River from Lees Ferry to Pearce Ferry, Arizona, 2021	2026	Sartain et al.		https://pubs.usgs.gov/publication/sir20265010
The Glen Canyon Dam, the flood of 1983, and a normal accident on the Colorado River corridor	2026-05-21	Rice	The 1983 flood along the Colorado River corridor pushed the Glen Canyon Dam to its breaking point and embodies Charles Perrow’s conception of a normal accident while also revealing limitations in his treatment of ecological dynamics. Fueled by a powerful El Niño arising in the Pacific Ocean, an abrupt and late season snow melt in the Rockies, and errors in forecasting basin-wide runoff, Lake Powell surged eight feet above full pool and just seven feet from the crest of the dam standing 710-feet high. This necessitated emergency releases through the spillway tunnels which triggered cavitation of the concrete lining and the underlying sandstone abutting the dam. Extending Perrow’s theory of normal accidents by integrating Andrew Pickering’s neo-materialist thought, I introduce the concept of “hydro-materiality” to foreground the distinctive and variable properties of water interacting with hydraulic infrastructure. Hydro-materiality illustrates the active, efficacious characteristics of water, the trans-scalar dynamics ranging from the Pacific to localized hydrology, and the liabilities of a dualist managerial framework envisioning the dam as a closed or bounded system insulated from, while also containing, the vagaries of nature. Flooding at the Glen Canyon Dam illustrates that catastrophic risk can arise due to the complexity and tight coupling derived of large-scale infrastructure and hydro-materiality in its various phase transformations and emergent, unpredictable characteristics. It is a catastrophic potential that is exacerbated when organizational actors are committed to a dualist, probabilistic, and technocratic frame of reference failing to recognize the materiality and performativity of water.	https://link.springer.com/10.1007/s12685-026-00392-1
Cool-season precipitation forecast evaluation over the headwaters of Central Valley and the Colorado River basin	05/2026	Tien and Gebremichael	Winter precipitation forecasting at sufficient lead times has several benefits, including aiding water allocation decisions and supporting individual water users’ decision-making. This study evaluates the performance of ensemble-mean coolseason (December through March) precipitation forecasts from individual models within the North American Multi-Model Ensemble (NMME) over the Colorado River basin and California’s Sacramento–San Joaquin–Tulare basins (hereafter referred to as the SST). These ensemble-mean forecasts are compared to a newly developed statistical forecasting model, using the rain-gauge-based Parameter-elevation Regressions on Independent Slopes Model (PRISM) as the reference product. While NMME models effectively capture the spatial pattern of mean precipitation, they struggle to predict yearto-year variability and extremes. Forecast skill is higher in the Colorado basin than in the SST Basin. Anomaly correlations between ensemble-mean NMME forecasts and observations vary by model and basin, with GEM5-NEMO and GFDLSPEAR showing relatively higher skill. Performance in forecasting droughts and wet/dry years remains inconsistent across models, with most models missing key events such as the 2023 and 2017 wet years and the 2022 drought. Simple statistical models using key atmospheric–oceanic predictors outperformed the more complex ensemble-mean NMME dynamical models in both basins. The most effective predictors were the Oceanic Niño Index, Tropical South Atlantic sea surface temperatures, and the Quasi-Biennial Oscillation for the SST Basin, and the North Atlantic Oscillation and Tropical North Atlantic sea surface temperatures for the Colorado basin.	https://link.springer.com/10.1007/s00382-026-08108-0
Revisiting the application of variable infiltration capacity (VIC) model in the Colorado River Basin using SMAP and GRACE	2026-04-03	Wang et al.	The Colorado River Basin (CRB) is a crucial water supply source experiencing prolonged drought conditions. Hydrologic models of the CRB have historically relied on streamflow calibration alone, limiting confidence in their representation of spatially distributed hydrologic processes. Here, we implemented a calibration and multi-source evaluation framework for the Variable Infiltration Capacity (VIC) model using observations from ground snow stations, streamflow records, and NASA’s Soil Moisture Active Passive (SMAP) and Gravity Recovery and Climate Experiment (GRACE) missions. After model calibration with snow and streamflow records, VIC achieved an excellent streamflow performance at key sub-basin outlets in the CRB (e.g., Nash-Sutcliffe Efficiency of 0.96 in the Upper Basin). Independent evaluations with SMAP further revealed a strong model performance in reproducing surface (R2 = 0.71) and root-zone (R2 = 0.81) soil moisture, with systematic elevationdependent patterns in the comparison. A multi-year evaluation with GRACE demonstrated a robust reproduction of basin-scale terrestrial water storage dynamics and their interannual variability (R2= 0.66–0.86). This multi-source evaluation framework establishes the VIC model capacity to represent subsurface water storage dynamics in different land cover types, providing enhanced confidence for supporting water management in the CRB.	https://www.nature.com/articles/s41598-026-47430-9
Minute 330 of the US–Mexico Water Treaty: A Testament to Transboundary Cooperation Amidst Drought in the Colorado River Basin	2026-03-25	Loera Alonso et al.	In 2024, the United States (US) and Mexico signed Minute 330, to address water scarcity in the Colorado River. Under Minute 330, Mexico committed to creating additional water savings through 2026, complementing conservation efforts by the US Lower Basin states during this period. In this paper, we examine the motivations behind Minute 330, its negotiations, and the state of its implementation to understand how it reflects the US–Mexico cooperative relationship amidst scarcity challenges in the basin. Our research takes a multi-method, qualitative approach that draws on semi-structured interviews with members of the Minute Negotiating Group from both countries and other interviewees with expertise on the post-2000 Colorado River Minute process from federal water agencies, NGOs, and universities, as well as members of US-state water agencies and Mexican water user leaders. We conclude that Minute 330 responded to water scarcity challenges in the basin that could not be addressed through prior minutes while setting an important precedent of cooperation and cross-border collaboration between the two countries amid unprecedented circumstances. These features take relevance in light of the post-2026 process and the need to develop additional regulations to manage the Colorado River both at the binational and the US national scale.	https://www.mdpi.com/2073-4441/18/7/775
Forensic Hydraulic Analysis of Floodplain Connectivity Driven by Historical Beaver Dams in Colorado Headwater Streams	2026-06-10	Schultz et al.	As ecosystem engineers, beavers (Castor canadensis) modify river corridor form through dam building. When beavers are removed from a river corridor, their unmaintained dams wash out, altering the stream's hydrologic regime. The assumption that beaver dams increase floodplain connectivity is frequently presumed but has not been directly quantified. To address this gap, we assessed changes in floodplain connectivity caused by the loss of beaver dams at three headwater streams in Colorado, USA. Using a forensic analysis of historical beaver activity, we developed two-dimensional hydraulic models to compare metrics of floodplain connectivity under historical (beaver-active) and present (no beaver activity) scenarios. At three simulated flood discharges, we quantified changes in the volume of water on the floodplain, the fraction of flow through the floodplain, the volumetric flux into the floodplain, and mean site and floodplain residence times. The loss of beaver dams decreased floodplain connectivity across all metrics (up to a 96.5% loss in connectivity) except mean floodplain residence time, which increased in the absence of dams. Sensitivity analysis results show that the flow state and condition of beaver dams can have reach-scale impacts on floodplain connectivity. Notably, while we observed floodplain disconnection due to the loss of beaver dams at each site, the magnitude of change varied depending on both site-specific characteristics and on the flood magnitude. We conclude that, in headwater streams, beaver dams play an important and quantifiable role in facilitating floodplain connectivity, and floodplain disconnection from the loss of dams has major implications for other ecological and geomorphic floodplain processes. These results are especially timely considering the increasing interest in beaver-related restoration.	https://onlinelibrary.wiley.com/doi/10.1002/rra.70165
Network‐wide assessment of soil water content calibration and sensitivity to biomass proxies using cosmic‐ray neutron sensing in the Roaring Fork Basin, Colorado	05/2026	Becker et al.	Soil water content (SWC) is a key state variable of the climate system but is often uncertain in water balance monitoring, especially in alpine environments. SWC measurements can be challenging in alpine environments due to the topography and rocky soils. In 2022, the US Geological Survey’s Next Generation Water Observing System Program began research to evaluate water balance monitoring technologies, including cosmic-ray neutron sensors (CRNS). This work evaluated the uncertainty resulting from network-wide calibration of CRNS for SWC monitoring in an alpine watershed and investigated the stability of the calibration parameters across space and time, focusing on potential influence of biomass dynamics. Fifteen stations with moderated and unmoderated (bare) CRNS were deployed and made operational within the Roaring Fork Basin in west-central Colorado. The root mean squared error of the network-wide calibration using the moderated CRNS was 0.042 or 0.047 cm3 cm−3, depending on the calibration equation used. Relative SWC dynamics from CRNS were correlated with the in situ probes with a correlation coefficient of 0.91 or 0.87 (depending on calibration equation). We did not find significant relationships between the calibration parameters and stationary site-specific variables. However, the calibration parameters derived from in situ probe SWC dynamics varied over time and were correlated with biomass proxies of cumulative growing degree-day, cumulative growing season index, and bare neutron counts. Future use of the CRNS network can leverage the reliable relative SWC data from network-wide calibration for watershed modeling and continue to research sensitivity of bare neutron measurements to biomass dynamics.	https://acsess.onlinelibrary.wiley.com/doi/10.1002/vzj2.70112
A novel method to estimate baseflow using open-source well data	2026-05-14	Celupica-Liu et al.	Baseflow, a proxy for groundwater discharge to streams, is vital for sustaining streamflow in periods of drought or low overland flow. Current methods for estimating baseflow include tracer-based approaches, which employ measurements of electrical conductivity, hydrochemical tracers, or environmental isotopes, and non-tracer-based approaches, such as graphical separation or numerical modeling. This technical note presents a novel, physics-based method for estimating baseflow using publicly available groundwater well data. The methodology was applied to the Roaring Fork River watershed in the Upper Colorado River Basin, USA. Groundwater level observations from 89 wells in the Roaring Fork River watershed were obtained for a 21-year period to interpolate mean static groundwater elevations. Hydraulic gradients toward the Roaring Fork River were elucidated from groundwater level contours. Hydraulic conductivity estimates in the shallow alluvium aquifer along the Roaring Fork River were obtained from pumping test data in 82 wells. On the basis of the average hydraulic gradient and the hydraulic conductivity estimates, a baseflow contribution of 9.6 m3/s from groundwater discharge was derived. This baseflow estimate divided by the measured mean annual streamflow results in a baseflow index of 0.6 for the Roaring Fork River watershed, compared to a baseflow index of 0.82 from graphical separation. Although no universally accepted ground-truth method for baseflow estimation exists, this study introduces a novel approach using groundwater flow physics. Given the scarcity of reliable, larger-scale baseflow estimates, and the importance of quantifying baseflow for water resource management, this study highlights the potential applicability of often underutilized groundwater data for hydrologic studies.	https://link.springer.com/10.1007/s10040-026-03087-2
Regional drying over the Western U.S. driven by enhanced atmospheric subsidence amid global moistening from 1980 to 2020	2026-04-16	Ding et al.	Abstract As the global climate has warmed anthropogenically over the past decades, the atmosphere across most of the globe has experienced significant moistening, except for a “moistening hole” (MH) -like change over the Western U.S. This regional anomaly since 1980 is at odds with the forced response of climate models to global warming in this region. Here, through analysis of a wide array of observations and water-tagging enabled simulations, we find that atmospheric forcing originating from the North Pacific contributes to the MH. A barotropic high-pressure circulation trend over the North Pacific, driven by observed sea surface temperature cooling in the tropical Eastern Pacific, enhances atmospheric sinking over the Western U.S. through equatorward cold air advection. This intensified atmospheric descent suppresses precipitation and weakens land-sourced evaporation, which are critical for replenishing atmospheric moisture in the region. We suggest that focusing on low-frequency changes of atmospheric vertical motion may offer insights into assessing and projecting climate stress and drought risks posed by long-term atmospheric moisture deficits in arid regions.	https://www.nature.com/articles/s41467-026-71818-w
Measure Less, Map More: Using Machine Learning, Physiography, and Prior Depth Maps to Extrapolate In‐Swath Snow Depth Measurements Across Mountain Basins	2026-05-28	Small et al.	Basin‐wide snow depth (SD) maps can support operational water supply assessments, but their availability is limited by measurement costs (airborne) or sampling constraints (satellite and drone). We present Swath‐random forest (RF), a methodology that trains random forests on SD measured within a narrow swath (<10% of a basin) to extrapolate basin‐wide depths. Using 68 LiDAR surveys from eight basins in Colorado and California, we evaluate two predictor cases: (a) physiography plus prior full‐basin snow‐depth maps and (b) physiography alone. For the first case, Swath‐RF with 2‐km‐wide swaths reproduces basin‐wide depth with low extrapolation absolute bias (0.019 m) and RMSE (0.21 m), and represents snow volume across topographic gradients and across dissimilar years. Errors are 2–3 times larger when using physiography alone. Swath‐RF enables basin‐wide mapping more frequently or across more basins, but at the cost of accuracy; applicability to other regions will depend on snow climate, physiography, and data availability.	https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2026GL121711