Graham Sexstone
Graham Sexstone is a Research Hydrologist with the USGS Colorado Water Science Center
Graham investigates snow and hydrological processes in mountainous environments of the United States that are critically important for understanding water resources and availability for the nation. Current projects use 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 snow processes are linked with water availability and water budgets. Graham received his PhD in Watershed Science from Colorado State University in 2016 and studied the importance of snow sublimation to seasonal snowpack variability.
Professional Experience
2017 to present: Research Hydrologist, USGS Colorado Water Science Center
2018 to present: Affiliate Faculty, Geosciences, Colorado State University
2012 to 2017: Hydrologist, USGS Colorado Water Science Center
Education and Certifications
2016. PhD, Watershed Science, Colorado State University
2012. M.S., Watershed Science, Colorado State University
2007. B.A., Geography, University of Vermont
Science and Products
Filter Total Items: 16
Climatological data for the Loch Vale watershed in Rocky Mountain National Park, Colorado, water years 1992-2019
This data release contains hourly means of climatological data collected by the U.S. Geological Survey (USGS) from 10/1/1991 to 9/30/2019 at three weather stations in the Loch Vale watershed in Rocky Mountain National Park (RMNP), Colorado. In order of increasing elevation, the three weather stations are Loch Vale meteorological station at RMNP, Colo. (Main weather station, USGS station...
Geospatial Fabric for the National Hydrologic Model Alaska Domain, version 1
This metadata record documents a geospatial dataset for the U.S. Geological Survey Precipitation Runoff Modeling System (PRMS) used to drive the National Hydrologic Model (NHM). The Alaska Geospatial Fabric v1 is the spatial representation of the hydrologic response units (HRUs) used for the PRMS NHM Alaska domain. These HRUs were generated using the twelve-digit Hydrologic Unit Code...
Data release in support of Runoff sensitivity to snow depletion curve representation within a continental scale hydrologic model
This data release includes simulation output from a modeling experiment conducted using the initial calibration of the conterminous United States (CONUS) application of the Precipitation-Runoff Modeling System (PRMS) (Hay, 2019) as implemented in the National Hydrologic Model (NHM) infrastructure (Regan et al, 2018). The study associated with this data release (Sexstone et al., 2019)...
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...
Filter Total Items: 25
Spatial variability in seasonal snowpack trends across the Rio Grande headwaters (1984 - 2017)
This study evaluated the spatial variability of trends in simulated snowpack properties across the Rio Grande headwaters of Colorado using the SnowModel snow evolution modeling system. SnowModel simulations were performed using a grid resolution of 100 m and 3-hourly time step over a 34-yr period (1984–2017). Atmospheric forcing was provided by phase 2 of the North American Land Data...
Authors
Graham A. Sexstone, Colin A. Penn, Glen E. Liston, Kelly Erika Gleason, C. David Moeser, David Clow
Changes in climate and land cover affect seasonal streamflow forecasts in the Rio Grande headwaters
Seasonal streamflow forecast bias, changes in climate, snowpack, and land cover, and the effects of these changes on relations between basin‐wide snowpack, SNOw TELemetry (SNOTEL) station snowpack, and seasonal streamflow were evaluated in the headwaters of the Rio Grande, Colorado. Results indicate that shifts in the seasonality of precipitation and changing climatology are consistent...
Authors
Colin A. Penn, David Clow, Graham A. Sexstone, Sheila F. Murphy
Runoff sensitivity to snow depletion curve representation within a continental scale hydrologic model
The spatial variability of snow water equivalent (SWE) can exert a strong influence on the timing and magnitude of snowmelt delivery to a watershed. Therefore, the representation of subgrid or subwatershed snow variability in hydrologic models is important for accurately simulating snowmelt dynamics and runoff response. The U.S. Geological Survey National Hydrologic Model infrastructure...
Authors
Graham A. Sexstone, Jessica M. Driscoll, Lauren Hay, John Christopher Hammond, Theodore B. Barnhart
Relating hydroclimatic change to streamflow, baseflow, and hydrologic partitioning in the Upper Rio Grande Basin, 1980 to 2015
Understanding how changing climatic conditions affect streamflow volume and timing is critical for effective water management. In the Rio Grande Basin of the southwest U.S., decreasing snowpack, increasing minimum temperatures, and decreasing streamflow have been observed in recent decades, but the effects of hydroclimatic changes on baseflow, or groundwater discharge to streams, have...
Authors
Christine A. Rumsey, Matthew Miller, Graham A. Sexstone
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...
Authors
Diogo Costa, Graham A. Sexstone, J.W. Pomeroy, Donald H. Campbell, David Clow, M. Alisa Mast
A 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...
Authors
Janice Brahney, Gregory A. Wetherbee, Graham A. Sexstone, C. Youngbull, P. Strong, Ruth C. Heindel
Science 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...
Authors
Gregory A. Wetherbee, Pamela H. Templar, Richard V. Pouyat, Stephen M. Decina, Brian M. Kerschner, Thomas H. Whitlow, Pamela E. Padgett, Donna Schwede, Jill Baron, David Clow, M. Alisa Mast, Graham A. Sexstone, Kristi H. Morris
Geometric 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...
Authors
Jessica E. Sanow, Steven R. Fassnacht, David J. Kamin, Graham A. Sexstone, William L. Bauerle, Iuliana Oprea
Snow 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...
Authors
Graham A. Sexstone, David Clow, Steven R. Fassnacht, Glen E. Liston, Christopher A. Hiemstra, John F. Knowles, Colin A. Penn
Comparison 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...
Authors
Graham A. Sexstone, David Clow, David Stannard, Steven R. Fassnacht
Water-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...
Authors
M. Alisa Mast, Sheila F. Murphy, David Clow, Colin A. Penn, Graham A. Sexstone
U.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...
Authors
Breton W. Bruce, David Clow, Molly A. Maupin, Matthew Miller, Gabriel B. Senay, Graham A. Sexstone, David Susong
Science and Products
Filter Total Items: 16
Climatological data for the Loch Vale watershed in Rocky Mountain National Park, Colorado, water years 1992-2019
This data release contains hourly means of climatological data collected by the U.S. Geological Survey (USGS) from 10/1/1991 to 9/30/2019 at three weather stations in the Loch Vale watershed in Rocky Mountain National Park (RMNP), Colorado. In order of increasing elevation, the three weather stations are Loch Vale meteorological station at RMNP, Colo. (Main weather station, USGS station...
Geospatial Fabric for the National Hydrologic Model Alaska Domain, version 1
This metadata record documents a geospatial dataset for the U.S. Geological Survey Precipitation Runoff Modeling System (PRMS) used to drive the National Hydrologic Model (NHM). The Alaska Geospatial Fabric v1 is the spatial representation of the hydrologic response units (HRUs) used for the PRMS NHM Alaska domain. These HRUs were generated using the twelve-digit Hydrologic Unit Code...
Data release in support of Runoff sensitivity to snow depletion curve representation within a continental scale hydrologic model
This data release includes simulation output from a modeling experiment conducted using the initial calibration of the conterminous United States (CONUS) application of the Precipitation-Runoff Modeling System (PRMS) (Hay, 2019) as implemented in the National Hydrologic Model (NHM) infrastructure (Regan et al, 2018). The study associated with this data release (Sexstone et al., 2019)...
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...
Filter Total Items: 25
Spatial variability in seasonal snowpack trends across the Rio Grande headwaters (1984 - 2017)
This study evaluated the spatial variability of trends in simulated snowpack properties across the Rio Grande headwaters of Colorado using the SnowModel snow evolution modeling system. SnowModel simulations were performed using a grid resolution of 100 m and 3-hourly time step over a 34-yr period (1984–2017). Atmospheric forcing was provided by phase 2 of the North American Land Data...
Authors
Graham A. Sexstone, Colin A. Penn, Glen E. Liston, Kelly Erika Gleason, C. David Moeser, David Clow
Changes in climate and land cover affect seasonal streamflow forecasts in the Rio Grande headwaters
Seasonal streamflow forecast bias, changes in climate, snowpack, and land cover, and the effects of these changes on relations between basin‐wide snowpack, SNOw TELemetry (SNOTEL) station snowpack, and seasonal streamflow were evaluated in the headwaters of the Rio Grande, Colorado. Results indicate that shifts in the seasonality of precipitation and changing climatology are consistent...
Authors
Colin A. Penn, David Clow, Graham A. Sexstone, Sheila F. Murphy
Runoff sensitivity to snow depletion curve representation within a continental scale hydrologic model
The spatial variability of snow water equivalent (SWE) can exert a strong influence on the timing and magnitude of snowmelt delivery to a watershed. Therefore, the representation of subgrid or subwatershed snow variability in hydrologic models is important for accurately simulating snowmelt dynamics and runoff response. The U.S. Geological Survey National Hydrologic Model infrastructure...
Authors
Graham A. Sexstone, Jessica M. Driscoll, Lauren Hay, John Christopher Hammond, Theodore B. Barnhart
Relating hydroclimatic change to streamflow, baseflow, and hydrologic partitioning in the Upper Rio Grande Basin, 1980 to 2015
Understanding how changing climatic conditions affect streamflow volume and timing is critical for effective water management. In the Rio Grande Basin of the southwest U.S., decreasing snowpack, increasing minimum temperatures, and decreasing streamflow have been observed in recent decades, but the effects of hydroclimatic changes on baseflow, or groundwater discharge to streams, have...
Authors
Christine A. Rumsey, Matthew Miller, Graham A. Sexstone
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...
Authors
Diogo Costa, Graham A. Sexstone, J.W. Pomeroy, Donald H. Campbell, David Clow, M. Alisa Mast
A 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...
Authors
Janice Brahney, Gregory A. Wetherbee, Graham A. Sexstone, C. Youngbull, P. Strong, Ruth C. Heindel
Science 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...
Authors
Gregory A. Wetherbee, Pamela H. Templar, Richard V. Pouyat, Stephen M. Decina, Brian M. Kerschner, Thomas H. Whitlow, Pamela E. Padgett, Donna Schwede, Jill Baron, David Clow, M. Alisa Mast, Graham A. Sexstone, Kristi H. Morris
Geometric 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...
Authors
Jessica E. Sanow, Steven R. Fassnacht, David J. Kamin, Graham A. Sexstone, William L. Bauerle, Iuliana Oprea
Snow 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...
Authors
Graham A. Sexstone, David Clow, Steven R. Fassnacht, Glen E. Liston, Christopher A. Hiemstra, John F. Knowles, Colin A. Penn
Comparison 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...
Authors
Graham A. Sexstone, David Clow, David Stannard, Steven R. Fassnacht
Water-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...
Authors
M. Alisa Mast, Sheila F. Murphy, David Clow, Colin A. Penn, Graham A. Sexstone
U.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...
Authors
Breton W. Bruce, David Clow, Molly A. Maupin, Matthew Miller, Gabriel B. Senay, Graham A. Sexstone, David Susong