Graham Sexstone
I am a Research Hydrologist in the USGS Colorado Water Science Center and Affiliate Faculty member of the Department of Geosciences at Colorado State University.
I investigate snow and hydrological processes in mountainous environments of the United States that are critically important for understanding water resources and availability for the nation. My current research uses a combination of field-based measurements, remote sensing observations, and physically based modeling over a range of spatial scales to better understand the spatial and temporal variability of snow water resources and how changes in snow processes are linked with changes to water availability, water budgets, and water quality. I received my PhD in Watershed Science from Colorado State University in 2016 and studied the importance of snow sublimation to seasonal snowpack variability. A list of my Science and Products are provided below and can also be viewed on my Google Scholar page.
Science and Products
SnowModel simulations and supporting observations for the north-central Colorado Rocky Mountains during water years 2011 through 2015
Preferential elution of ionic solutes in melting snowpacks: Improving process understanding through field observations and modeling in the Rocky Mountains
A new sampler for the collection and retrieval of dry dust deposition
Science needs for continued development of total nitrogen deposition budgets in the United States
Geometric versus anemometric surface roughness for a shallow accumulating snowpack
Snow sublimation in mountain environments and its sensitivity to forest disturbance and climate warming
Comparison of methods for quantifying surface sublimation over seasonally snow-covered terrain
Water-quality response to a high-elevation wildfire in the Colorado Front Range
U.S. Geological Survey National Water Census: Colorado River Basin Geographic Focus Area Study
Spatial patterns of atmospheric deposition of nitrogen and sulfur using ion-exchange resin collectors in Rocky Mountain National Park, USA
Science and Products
- Science
- Data
Filter Total Items: 13
SnowModel simulations and supporting observations for the north-central Colorado Rocky Mountains during water years 2011 through 2015
This data release includes simulation output from SnowModel (Liston and Elder, 2006), a well-validated process-based snow modeling system, and supporting snow, meteorological, and streamflow observations from the water years 2011 through 2015 (October 1, 2010, through September 30, 2015) across a 3,600 square kilometer model domain in the north-central Colorado Rocky Mountains. For each water year - Multimedia
- Publications
Filter Total Items: 21
Preferential elution of ionic solutes in melting snowpacks: Improving process understanding through field observations and modeling in the Rocky Mountains
The preferential elution of ions from melting snowpacks is a complex problem that has been linked to temporary acidification of water bodies. However, the understanding of these processes in snowpacks around the world, including the polar regions that are experiencing unprecedented warming and melting, remains limited despite being instrumental in supporting climate change adaptation.In this studyAuthorsDiogo Costa, Graham A. Sexstone, J.W. Pomeroy, Donald H. Campbell, David W. Clow, Alisa MastA new sampler for the collection and retrieval of dry dust deposition
Atmospheric dust can influence biogeochemical cycles, accelerate snowmelt, and affect air, water quality, and human health. Yet, the bulk of atmospherically transported material remains poorly quantified in terms of total mass fluxes and composition. This lack of information stems in part from the challenges associated with measuring dust deposition. Here we report on the design and efficacy of aAuthorsJ. Brahney, Gregory A. Wetherbee, Graham A. Sexstone, C. Youngbull, P. Strong, Ruth C. HeindelScience needs for continued development of total nitrogen deposition budgets in the United States
The objectives of this white paper are to describe the state of the science with respect to total Nr deposition budgets in North America and the research needed to improve these budgets from both a measurement and modeling standpoint. The document is intended to serve as a plan for TDep research activities but also, more broadly, to provide program managers, natural resource managers, policy makeAuthorsGregory A. Wetherbee, Pamela H. Templar, Richard V. Pouyat, Stephen M. Decina, Brian M. Kerschner, Thomas H. Whitlow, Pamela E. Padgett, Donna B. Schwede, Jill Baron, David Clow, Alisa Mast, Graham A. Sexstone, Kristi H. MorrisGeometric versus anemometric surface roughness for a shallow accumulating snowpack
When applied to a snow-covered surface, aerodynamic roughness length, z0, is typically considered as a static parameter within energy balance equations. However, field observations show that z0 changes spatially and temporally, and thus z0 incorporated as a dynamic parameter may greatly improve models. To evaluate methods for characterizing snow surface roughness, we compared concurrent estimatesAuthorsJessica E. Sanow, Steven R. Fassnacht, David J. Kamin, Graham A. Sexstone, William L. Bauerle, Iuliana OpreaSnow sublimation in mountain environments and its sensitivity to forest disturbance and climate warming
Snow sublimation is an important component of the snow mass balance, but the spatial and temporal variability of this process is not well understood in mountain environments. This study combines a process‐based snow model (SnowModel) with eddy covariance (EC) measurements to investigate (1) the spatio‐temporal variability of simulated snow sublimation with respect to station observations, (2) theAuthorsGraham A. Sexstone, David W. Clow, Steven R. Fassnacht, Glen E. Liston, Christopher A. Hiemstra, John F. Knowles, Colin A. PennComparison of methods for quantifying surface sublimation over seasonally snow-covered terrain
Snow sublimation can be an important component of the snow-cover mass balance, and there is considerable interest in quantifying the role of this process within the water and energy balance of snow-covered regions. In recent years, robust eddy covariance (EC) instrumentation has been used to quantify snow sublimation over snow-covered surfaces in complex mountainous terrain. However, EC can be chaAuthorsGraham A. Sexstone, David W. Clow, David I. Stannard, Steven R. FassnachtWater-quality response to a high-elevation wildfire in the Colorado Front Range
Water quality of the Big Thompson River in the Front Range of Colorado was studied for 2 years following a high‐elevation wildfire that started in October 2012 and burned 15% of the watershed. A combination of fixed‐interval sampling and continuous water‐quality monitors was used to examine the timing and magnitude of water‐quality changes caused by the wildfire. Prefire water quality was well chaAuthorsAlisa Mast, Sheila F. Murphy, David W. Clow, Colin A. Penn, Graham A. SexstoneU.S. Geological Survey National Water Census: Colorado River Basin Geographic Focus Area Study
Introduction The U.S. Geological Survey’s (USGS) concept of a national census (or accounting) of water resources has evolved over the last several decades as the Nation has experienced increasing concern over water availability for multiple competing uses. The implementation of a USGS National Water Census was described in the USGS 2007 science strategy document that identified the highest prioritAuthorsBreton W. Bruce, David W. Clow, Molly A. Maupin, Matthew P. Miller, Gabriel B. Senay, Graham A. Sexstone, David D. SusongSpatial patterns of atmospheric deposition of nitrogen and sulfur using ion-exchange resin collectors in Rocky Mountain National Park, USA
Lakes and streams in Class 1 wilderness areas in the western United States (U.S.) are at risk from atmospheric deposition of nitrogen (N) and sulfur (S), and protection of these resources is mandated under the Federal Clean Air Act and amendments. Assessment of critical loads, which are the maximum exposure to pollution an area can receive without adverse effects on sensitive ecosystems, requiresAuthorsDavid W. Clow, Heidi Roop, Leora Nanus, Mark Fenn, Graham A. Sexstone