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Title	Date	Authors	Cite	Abstract
High-resolution models better simulate historical snowpack declines in the Upper Colorado River Basin	2026-03-14	Dixit et al.	Dixit, Ankur, Stefan Rahimi, Lei Huang, Keith N Musselman, Julie A Vano, Nans Addor, and Flavio Lehner. “High-Resolution Models Better Simulate Historical Snowpack Declines in the Upper Colorado River Basin.” Environmental Research Letters 21, no. 5 (March 14, 2026): 054012. https://doi.org/10.1088/1748-9326/ae4113.	The Colorado River supplies water to 40 million people, 4.5 million acres of irrigated land, seven US states, over two dozen federally recognized and sovereign tribes and Mexico. River discharge is strongly controlled by snowpack accumulation and melt in the headwater regions, making upper-basin snow dynamics a primary driver of water availability throughout the basin. Therefore, changes in snow water equivalent (SWE) are critical for water resources planning in the Upper Colorado River Basin (UCRB), yet there is considerable uncertainty even in historical SWE trends. We compare historical UCRB SWE trends across various gridded snow products, including new Weather Research and Forecasting simulations at 45, 9, and 3 km resolution, against snow telemetry station data. We find that SWE trends are systematically amplified with higher model resolution and that high resolution (<10 km) is needed to accurately capture not only SWE amounts but also historical SWE declines across high-elevation mountains. Trend amplification primarily results from higher resolution simulations having higher snowfall due to stronger orographic forcing, an effect further modulated by synoptics. This is confirmed in a set of alternative historical realizations from a downscaled climate model large ensemble, which, despite a tendency for SWE declines, highlight the important role of internal variability in historical UCRB SWE trends. These results demonstrate that model resolution plays an important role in shaping assessments of snowrelated climate change, with implications for a wide range of impact studies.
Synoptic-Scale Systems Control Total Winter Sublimation at an Alpine Site	04/2026	Hogan et al.	Hogan, Daniel, Eli Schwat, Ethan Gutmann, Julie Vano, and Jessica D. Lundquist. “Synoptic-Scale Systems Control Total Winter Sublimation at an Alpine Site.” Journal of Hydrometeorology 27, no. 4 (2026): 529–47. https://doi.org/10.1175/JHM-D-25-0143.1.	Abstract Sublimation is an important yet uncertain component of the water balance in snow-dominated regions. Models that parameterize sublimation as a function of temperature show that sublimation has increased over recent decades, and this has been identified as a possible reason for declining Colorado River streamflow. However, sublimation increases with wind speed and water vapor gradients and cannot be well explained by temperature alone. Thus, we hypothesize that most accumulation season sublimation occurs during distinct weather events. To test this hypothesis, we combined 2 years of meteorological observations spanning site-to-synoptic scales from three field campaigns in a Colorado mountain valley and identified the events that produced the most sublimation, classifying them by duration and intensity. We found that approximately 60% of winter sublimation occurred during a small number of discrete events (14% of the season). These events coincided with either short sunny, dry periods or long storm events that brought new snowfall followed by blowing snow. Using these classified events and synoptic-scale reanalysis, we trained a random forest classifier to estimate long sublimation event occurrences and test whether they increased over the past four decades. The model performed well (average precision = 0.73; balanced accuracy = 79%), and results were most strongly associated with winter mean 500-hPa wind speed and total observed precipitation. Event occurrence varied considerably year to year with no significant long-term trend. In all, our findings show that accurately representing seasonal sublimation requires capturing discrete events driven by identifiable synoptic and local meteorological conditions. Significance Statement Sublimation, defined as the direct phase transition from ice to water vapor, plays an important, yet uncertain, role in determining how much snow is available to melt at the end of each winter. We wanted to reduce this uncertainty by identifying the types of weather events that cause the most sublimation to occur. We found that a majority of winter sublimation (60%) occurs over just a small fraction of the winter (14%), and large-scale weather dynamics can be used to indicate when these sublimation events occur. Our results provide new insight into how large-scale processes impact sublimation in complex terrain and point toward a better understanding of the major processes that cause sublimation to vary over time.
Sublimation of Snow	2024-04-02	Lundquist et al.	Lundquist, Jessica D., Julie Vano, Ethan Gutmann, Daniel Hogan, Eli Schwat, Michael Haugeneder, Emilio Mateo, et al. “Sublimation of Snow.” Bulletin of the American Meteorological Society, April 2, 2024. https://doi.org/10.1175/BAMS-D-23-0191.1.	Abstract Snow is a vital part of water resources, and sublimation may remove 10% to 90% of snowfall from the system. To improve our understanding of the physics that govern sublimation rates, as well as how those rates might change with the climate, we deployed an array of four towers with over 100 instruments from NCAR’s Integrated Surface Flux System from November 2022 to June 2023 in the East River Watershed, Colorado, in conjunction with the U.S. Department of Energy’s Surface Atmosphere Integrated Field Laboratory (SAIL) and the National Oceanic and Atmospheric Administration (NOAA)’s Study of Precipitation, the Lower Atmosphere and Surface for Hydrometeorology (SPLASH) campaigns. Mass balance observations, snow pits, particle flux sensors, and terrestrial lidar scans of the evolving snowfield demonstrated how blowing snow influences sublimation rates, which we quantified with latent heat fluxes measured by eddy covariance systems at heights 1 to 20 m above the snow surface. Detailed temperature profiles at finer resolutions highlighted the role of the stable boundary layer. Four-stream radiometers indicated the important role of changing albedo in the energy balance and its relationship to water vapor losses. Collectively, these observations span scales from seconds to seasons, from boundary layer turbulence to valley-circulation to mesoscale meteorology. We describe the field campaign, highlights in the observations, and outreach and education products we are creating to facilitate cross-disciplinary dialogue and convey relevant findings to those seeking to better understand Colorado River snow and streamflow.
A Collaborative, In Situ Mountain Hydrology NASA Test Bed	2024	Aspen Global Change Institute et al.	Aspen Global Change Institute, Julie Vano, Tanya Petach, Jeffrey Deems, Mark S. Raleigh, James Arnott, Elise Osenga, and Joseph Hamman. “A Collaborative, In Situ Mountain Hydrology NASA Test Bed.” Aspen Global Change Institute, 2024. https://doi.org/10.69925/VCBQ9771.	Beginning primarily as snowmelt from the Rocky Mountains, the Colorado River supplies water to over 40 million people in seven U.S. states and Mexico. As demand for water grows and climate-driven drought threatens supply, there is an urgent need to advance decision-relevant hydrologic research in this region, which serves as an example for similarly positioned mountain headwaters around the world. Within this report we share the design for a collaborative process for testing innovative approaches to doing research—a test bed for short—that leverages existing research efforts and articulates strategies for accelerating the science resource managers are seeking to address this need. We designed this test bed by 1) engaging researchers and those who forecast, operate, and manage resources and 2) by employing collaborative science expertise and network analysis. Our activities involved investigations into areas of untapped potential (including 15 events on a listening tour), the research landscape, and the user needs landscape, which we drew upon to design our proposed test bed. This test bed is built from a suite of recommendations (listed below) based on those explorations. The proposed test bed supports an approach to conducting mountain hydrology research that complements NASA science goals and that is centered on collaborations and strategic monitoring, modeling, and data science enhanced by local partners to:  Accelerate understanding of mountain water cycles and improve forecasts in a rapidly changing world;  Use long-term monitoring to calibrate, validate, complement, and enhance satellite data and land surface models; and  Cultivate learning and community building among scientists, within and across institutions, and in collaboration with research users. In general, we focus on systematic ways to build on what already exists (vs. creating something entirely new). Through our work in designing the test bed, we utilize network analysis, user needs synthesis, and collaboration management (bringing people together in ways that support collaborative science)—tools that will also help to further refine and sustain the effort. This report develops a suite of broadly applicable recommendations for future work (summarized below), as well as action items more specific to the NASA Terrestrial Hydrology program.
The Press and Pulse of Climate Change: Extreme Events in the Colorado River Basin	2022-06-21	McCoy et al.	McCoy, Amy L., Katharine L. Jacobs, Julie A. Vano, J. Keaton Wilson, Season Martin, Angeline G. Pendergrass, and Rob Cifelli. “The Press and Pulse of Climate Change: Extreme Events in the Colorado River Basin.” JAWRA Journal of the American Water Resources Association, June 21, 2022, 1752-1688.13021. https://doi.org/10.1111/1752-1688.13021.	Extremes in temperature and precipitation are associated with damaging floods, prolonged drought, destructive wildfires, agricultural challenges, compromised human health, vulnerable infrastructure, and threatened ecosystems and species. Often, the steady and progressive trends (or presses) of rising global temperature are the central focus in how climate impacts are described. However, observations of extreme weather events (or pulses) increasingly show that the intensity, duration and/or frequency of acute events are also changing, resulting in greater impacts on communities and the environment. Describing how the influence of extreme events may shape water management in the Colorado River Basin in clear terms is critical to sound future planning and efforts to manage risk. Three scenario planning workshops in 2019 and 2020 were held as part of a Colorado River Conversations series, identifying potential impacts from multiple intersecting extreme events. Water managers identified climate-related events of concern in the Colorado River Basin that necessitate greater attention and adaptive responses. To support efforts to include consideration of climate-change-driven extremes in water management and planning, we explore the current state of knowledge at the confluence of long-term climate shifts and extreme weather in the Colorado River Basin related to the events of concern that were identified by scenario planning participants.
Featured Collection Introduction: Severe Sustained Drought Revisited: Managing the Colorado River System in Times of Water Shortage 25 Years Later — Part I	2022	Frisvold et al.	Frisvold, George B., Linda M. Fernandez, Flavio Lehner, Stephanie A. McAfee, Sharon Megdal, Elizabeth Payton, Jack Schmidt, Julie Vano, and Connie Woodhouse. “Featured Collection Introduction: Severe Sustained Drought Revisited: Managing the Colorado River System in Times of Water Shortage 25 Years Later — Part I.” JAWRA Journal of the American Water Resources Association 58, no. 5 (2022): 597–603. https://doi.org/https://doi.org/10.1111/1752-1688.13062.
Featured Collection introduction: Severe sustained drought revisited managing the Colorado River system in times of water shortage 25 years later—Part II	2022	Frisvold et al.	Frisvold, George B., Linda M. Fernandez, Flavio Lehner, Stephanie A. McAfee, Sharon Megdal, Elizabeth Payton, Jack Schmidt, Julie Vano, and Connie Woodhouse. “Featured Collection Introduction: Severe Sustained Drought Revisited Managing the Colorado River System in Times of Water Shortage 25 Years Later—Part II.” JAWRA Journal of the American Water Resources Association 58, no. 6 (2022): 1049–52. https://doi.org/https://doi.org/10.1111/1752-1688.13085.
Winter melt trends portend widespread declines in snow water resources	05/2021	Musselman et al.	Musselman, Keith N., Nans Addor, Julie A. Vano, and Noah P. Molotch. “Winter Melt Trends Portend Widespread Declines in Snow Water Resources.” Nature Climate Change 11, no. 5 (2021): 418–24. https://doi.org/10.1038/s41558-021-01014-9.
A community‐supported weather and soil moisture monitoring database of the Roaring Fork catchment of the Colorado River Headwaters	03/2021	Osenga et al.	Osenga, Elise C., Julie A. Vano, and James C. Arnott. “A Community‐supported Weather and Soil Moisture Monitoring Database of the Roaring Fork Catchment of the Colorado River Headwaters.” Hydrological Processes 35, no. 3 (2021). https://doi.org/10.1002/hyp.14081.	Local community interest in better understanding regional climate change impacts has motivated the establishment of a long-term soil moisture and weather observation network in the Roaring Fork catchment of the Colorado River Headwaters. This catchmentwide suite of 10 stations, installed between 2012 and 2020, collects frequent, fixedinterval data on soil moisture, soil temperature, rain, air temperature, relative humidity, and (at some stations) snow across an elevational gradient from 1800 to 3680 m. In this paper we provide a description of the data this network provides, how data are accessed, and how this community-supported effort has resulted in data that support mountain hydrology research with applications for resource management and climate change adaptation decision making. All data from this network are publicly available.
The potential to reduce uncertainty in regional runoff projections from climate models	2019	Lehner et al.	Lehner, Flavio, A. W. Wood, J.A. Vano, D. M. Lawrence, Martyn P. Clark, and Justin S. Mankin. “The Potential to Reduce Uncertainty in Regional Runoff Projections from Climate Models.” Nature Climate Change 9 (2019): 926–33. https://doi.org/10.1038/s41558-019-0639-x.
DOs and DON'Ts for using climate change information for water resource planning and management: guidelines for study design	12/2018	Vano et al.	Vano, Julie A., Jeffrey R. Arnold, Bart Nijssen, Martyn P. Clark, Andrew W. Wood, Ethan D. Gutmann, Nans Addor, Joseph Hamman, and Flavio Lehner. “DOs and DON’Ts for Using Climate Change Information for Water Resource Planning and Management: Guidelines for Study Design.” Climate Services 12 (2018): 1–13. https://doi.org/10.1016/j.cliser.2018.07.002.	Water managers are actively incorporating climate change information into their long- and short-term planning processes. This is generally seen as a step in the right direction because it supplements traditional methods, providing new insights that can help in planning for a non-stationary climate. However, the continuous evolution of climate change information can make it challenging to use available information appropriately. Advice on how to use the information is not always straightforward and typically requires extended dialogue between information producers and users, which is not always feasible. To help navigate better the everchanging climate science landscape, this review is organized as a set of nine guidelines for water managers and planners that highlight better practices for incorporating climate change information into water resource planning and management. Each DOs and DON'Ts recommendation is given with context on why certain strategies are preferable and addresses frequently asked questions by exploring past studies and documents that provide guidance, including real-world examples mainly, though not exclusively, from the United States. This paper is intended to provide a foundation that can expand through continued dialogue within and between the climate science and application communities worldwide, a two-way information sharing that can increase the actionable nature of the information produced and promote greater utility and appropriate use.
Characterizing Uncertainty of the Hydrologic Impacts of Climate Change	6/2016	Clark et al.	Clark, Martyn P., Robert L. Wilby, Ethan D. Gutmann, Julie A. Vano, Subhrendu Gangopadhyay, Andrew W. Wood, Hayley J. Fowler, Christel Prudhomme, Jeffrey R. Arnold, and Levi D. Brekke. “Characterizing Uncertainty of the Hydrologic Impacts of Climate Change.” Current Climate Change Reports 2, no. 2 (2016): 55–64. https://doi.org/10.1007/s40641-016-0034-x.	The high climate sensitivity of hydrologic systems, the importance of those systems to society, and the imprecise nature of future climate projections all motivate interest in characterizing uncertainty in the hydrologic impacts of climate change. We discuss recent research that exposes important sources of uncertainty that are commonly neglected by the water management community, especially, uncertainties associated with internal climate system variability, and hydrologic modeling. We also discuss research exposing several issues with widely used climate downscaling methods. We propose that progress can be made following parallel paths: first, by explicitly characterizing the uncertainties throughout the modeling process (rather than using an ad hoc Bensemble of opportunity^) and second, by reducing uncertainties through developing criteria for excluding poor methods/models, as well as with targeted research to improve modeling capabilities. We argue that such research to reveal, reduce, and represent uncertainties is essential to establish a defensible range of quantitative hydrologic storylines of climate change impacts.
A sensitivity-based approach to evaluating future changes in Colorado River discharge	2/2014	Vano and Lettenmaier	Vano, Julie A., and Dennis P. Lettenmaier. “A Sensitivity-Based Approach to Evaluating Future Changes in Colorado River Discharge.” Climatic Change 122, no. 4 (2014): 621–34. https://doi.org/10.1007/s10584-013-1023-x.	Projections of a drier, warmer climate in the U.S. Southwest would complicate management of the Colorado River system—yet these projections, often based on coarse resolution global climate models, are quite uncertain. We present an approach to understanding future Colorado River discharge based on land surface characterizations that map the Colorado River basin’s hydrologic sensitivities (e.g., changes in streamflow magnitude) to annual and seasonal temperature and precipitation changes. The approach uses a process-based macroscale land surface model (LSM; in this case, the Variable Infiltration Capacity hydrologic model, although methods are applicable to any LSM) to develop sensitivity maps (equivalent to a simple empirical model), and uses these maps to evaluate long-term annual streamflow responses to future precipitation and temperature change. We show that global climate model projections combined with estimates of hydrologic sensitivities, estimated for different seasons and at different change increments, can provide a basis for approximating cumulative distribution functions of streamflow changes similar to more common, computationally intensive full-simulation approaches that force the hydrologic model with downscaled future climate scenarios. For purposes of assessing risk, we argue that the sensitivity-based approach produces viable first-order estimates that can be easily applied to newly released climate information to assess underlying drivers of change and bound, at least approximately, the range of future streamflow uncertainties for water resource planners.
Understanding Uncertainties in Future Colorado River Streamflow	01/2014	Vano et al.	Vano, Julie A., Bradley Udall, Daniel R. Cayan, Jonathan T. Overpeck, Levi D. Brekke, Tapash Das, Holly C. Hartmann, et al. “Understanding Uncertainties in Future Colorado River Streamflow.” Bulletin of the American Meteorological Society 95, no. 1 (2014): 59–78. https://doi.org/10.1175/BAMS-D-12-00228.1.
Hydrologic sensitivities of Colorado River runoff to changes in precipitation and temperature	06/2012	Vano et al.	Vano, Julie A., Tapash Das, and Dennis P. Lettenmaier. “Hydrologic Sensitivities of Colorado River Runoff to Changes in Precipitation and Temperature.” Journal of Hydrometeorology 13, no. 3 (2012): 932–49. https://doi.org/10.1175/JHM-D-11-069.1.	The Colorado River is the primary water source for much of the rapidly growing southwestern United States. Recent studies have projected reductions in Colorado River flows from less than 10% to almost 50% by midcentury because of climate change—a range that has clouded potential management responses. These differences in projections are attributable to variations in climate model projections but also to differing land surface model (LSM) sensitivities. This second contribution to uncertainty—specifically, variations in LSM runoff change with respect to precipitation (elasticities) and temperature (sensitivities)—are evaluated here through comparisons of multidecadal simulations from five commonly used LSMs (Catchment, Community Land Model, Noah, Sacramento Soil Moisture Accounting model, and Variable Infiltration Capacity model) all applied over the Colorado River basin at 1/88 latitude by longitude spatial resolution. The annual elasticity of modeled runoff (fractional change in annual runoff divided by fractional change in annual precipitation) at Lees Ferry ranges from two to six for the different LSMs. Elasticities generally are higher in lower precipitation and/or runoff regimes; hence, the highest values are for models biased low in runoff production, and the range of elasticities is reduced to two to three when adjusted to current runoff climatology. Annual temperature sensitivities (percent change in annual runoff per degree change in annual temperature) range from declines of 2% to as much as 9% per degree Celsius increase at Lees Ferry. For some LSMs, small areas, primarily at midelevation, have increasing runoff with increasing temperature; however, on a spatial basis, most sensitivities are negative.
Evaluating climate change over the Colorado River basin using regional climate models	2011-07-07	Gao et al.	Gao, Yanhong, Julie A. Vano, Chunmei Zhu, and Dennis P. Lettenmaier. “Evaluating Climate Change over the Colorado River Basin Using Regional Climate Models.” Journal of Geophysical Research 116, no. D13 (July 7, 2011). https://doi.org/10.1029/2010JD015278.
The importance of warm season warming to western U.S. streamflow changes	12/2011	Das et al.	Das, Tapash, David W. Pierce, Daniel R. Cayan, Julie A. Vano, and Dennis P. Lettenmaier. “The Importance of Warm Season Warming to Western U.S. Streamflow Changes.” Geophysical Research Letters 38, no. 23 (2011): n/a-n/a. https://doi.org/10.1029/2011GL049660.