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Global Rivers Group
@Virginia Tech
We use satellites, models, and fieldwork to study Earth's freshwater
We're an academic research group in the Department of Geosciences at Virginia Tech. We are recruiting students and postdocs who are interested in using emerging technology to solve problems involving freshwater resources.
What we do
We study inland waters using satellite data, fieldwork, and computer models. We seek to understand how climate change and land use are altering the global water cycle, in particular river and lake hydrology. With rapid advancements in sensor technology, computing power, and model sophistication, it is an exciting time to be studying freshwater at the global scale.
Why we do it
Water is widely considered to be the world’s most vital natural resource, yet freshwater systems are being rapidly degraded by human activities. Our work is motivated by a desire to promote the conservation, management, and understanding of Earth's surface water resources.
News
Updated June 11, 2025
Jun 8, 2025—Paper published in Geophysical Research Letters titled, "Mapping Reservoir Water Surface Area in the Contiguous United States Using the High-Temporal Harmonized Landsat and Sentinel (HLS) Data at a Sub-Weekly Time Scale". This paper generated accurate, high-frequency observations of lake surface areas over the contiguous U.S. using the Harmonized Landsat Sentinel-2 data product. The study was led by Anshul Yadav and supervised by Dr. Huilin Gao at Texas A&M University. George Allen and Katie McQuillan are co-authors. https://doi.org/10.1029/2024GL114046
Jun 4, 2025—Paper published in Earth System Science Data titled, "Mapping the world’s inland surface waters: an update to the Global Lakes and Wetlands Database (GLWD v2)". Led by Bernhard Lehner at McGill University, this paper presents the first fine-scale harmonized global map of inland surface waters. George is a co-author. https://doi.org/10.5194/essd-17-2277-2025
Jun 3, 2025—George is promoted to Associate Professor with tenure at Virginia Tech! https://news.vt.edu/articles/2025/06/bov-promotion-tenure-2025.html
Jun 1, 2025—The Washington Post covers Hana's paper on SWOT's ability to observe flow waves traveling down Earth's rivers: wapo.st/43UuquB
May 29, 2025—Carter's paper published in Geophysical Research Letters, "The Widths of Rivers and Streams Across Spatial Scales: A Framework for Improving River-Atmosphere Biogeochemical Exchange Estimates". This paper shows that river widths can be represented at different stream orders using a predictable log-normal distribution, which when summed across a river network, forms a characteristic Pareto distribution. Very nicely done, Carter!
https://doi.org/10.1029/2025GL115713
May 27, 2025—Hana starts her summer internship at the Jet Propulsion Laboratory (JPL) in Pasadena, CA. She will work with Dr. Cedric David and Dr. Arnaud Cerbelaud on studying rivers with the SWOT satellite. Have fun, Hana! 🚀
May 21, 2025—NASA publishes a news article covering Hana's recent study on observing flow waves with SWOT: https://www.nasa.gov/missions/swot/nasa-french-satellite-spots-large-scale-river-waves-for-first-time/
May 16, 2025—Paper published in Earth System Science Data, entitled "Satellite Altimetry-based Extension of global-scale in situ river discharge Measurements (SAEM)". This paper, led by Peyman Saemian at the University of Stuttgart, presents the largest satellite-based dataset of river discharge over 47,000 gauges globally. Molly, Ryan and George are co-authors on this study and Virginia Tech undergraduates students, Shaurya Prakash, Jordan Lavey and Torian Cooper, contributed to this study's analysis. https://doi.org/10.5194/essd-17-2063-2025
May 15, 2025—New paper published in Water Resources Research: "Global River Topology (GRIT): A bifurcating river hydrography. This paper presents the first global river network with realistic downstream bifurcations included. It was led by Michel Wortmann at the University of Oxford. https://doi.org/10.1029/2024WR038308 Press release, EOS Research Spotlight article
May 14, 2025—Hana's paper, "SWOT captures hydrologic waves traveling down rivers", Geophysical Research Letters. This paper shows that SWOT data can be processed to produce "spatial hydrographs" and flow waves can be observed across space, not just time. A whole new way of studying river hydrology! Congratulations, Hana! https://doi.org/10.1029/2024GL113875
May 9, 2025—New paper published in Earth System Science Data titled "Global Methane Budget 2000–2020". This is a community consensus paper, which describes the current best estimates of the global methane budget. Led by Marielle Saunois at the University of Paris-Saclay.
https://doi.org/10.5194/essd-17-1873-2025
May 3, 2025—Paper published in Water Resources Research titled "A First Look at River Discharge Estimation From SWOT Satellite Observations". This collaborative paper from the SWOT Discharge Algorithms Working Group (DAWG), and led by the Kostas Andreadis at UMass Amherst, presents the first results from the SWOT discharge product. George and Ryan Riggs are coauthors.
https://doi.org/10.1029/2024GL114185
May 2, 2025—Paper published in Environmental Toxicology and Chemistry titled "Insights into the in-situ degradation and fragmentation of macroplastics in a low-order riverine system". Led by Austin Gray at VT Biological Sciences, this paper documents the processes by which plastic degrades and fragments into microplastic in small, low-order stream environments. Luisana is a coauthor of this study. https://doi.org/10.1093/etojnl/vgaf116
Apr 29, 2025—Luisana successfully defends her Master's Thesis on satellite remote sensing of microplastics in rivers. Excellent presentation to a standing-room-only crowd. Congratulations, Luisana!
Apr 20, 2025—Paper published in Water Resources Research titled "Spatial Hydrographs of River Flow and Their Analysis for Peak Event Detection in the Context of Satellite Sampling". This study was led by Dr. Arnaud Cerbelaud at the Jet Propulsion Laboratory and uses gauge data to study flow waves propagating down rivers. George and Hana are co-authors on this study.
https://doi.org/10.1029/2024WR038444
Apr 18, 2025—Luisana presents her research on microplastics at the Carolinas Society of Environmental Toxicology and Chemistry Annual Meeting in Charleston, SC.
Apr 11, 2025—David, Hana and Yohtaro present at the Virginia Tech Office for GIS and Remote Sensing Research 2025 Symposium. Yohtaro won third place 🏆 for best presentation! Great job, all!
Apr 3-4, 2025—Hana, Yohtaro, Emily, David, Molly and Luisana present at the 2025 Department of Geosciences Graduate Student Research Symposium at Virginia Tech. Emily won a best talk award 🏆 and Molly won the best "upgoer5" award 🏆. Well done, everyone!
Mar 25, 2025—Katie publishes a paper in Earth and Space Science entitled, "Estimating wind direction and wind speed over lakes with SWOT and Sentinel-1 satellite observations". This is the first study to demonstrate that SWOT and Sentinel-2 SAR backscatter can be used to resolve wind fields at very high-resolution over lakes and resolution. https://doi.org/10.1029/2024EA003971
- VT News article on the paper: https://news.vt.edu/articles/2025/02/science-radar-lake.html
Mar 22, 2025—Luisana wins a VT Geosciences Intro Level Teaching Award 🏆! Congratulations, Luisana and thank you for doing a great job educating our undergraduate students!
Mar 19, 2025—Paper published in Water Resources Research entitled "The Surface Water and Ocean Topography Mission (SWOT) Prior Lake Database (PLD): Lake Mask and Operational Auxiliaries" led by Jida Wang at University of Illinois. The paper presents the official prior lake dataset for the NASA/CNES SWOT satellite mission. https://doi.org/10.1029/2023WR036896
Feb 26, 2025—Yohtaro wins an AGU Outstanding Student Presentation Award 🏆 (OSPA)! This honor is awarded for only the most exceptional presentations during AGU 2024. Congratulations, Yohtaro!
Jan 22, 2025—Paper led by Ben Gorr at Texas A&M University published in Journal of Spacecraft and Rockets titled, "Decentralized Satellite Constellation Replanning for Event Observation". This paper describes a new decentralized method to capture events of interest on Earth's surface using satellite sensor webs. https://arc.aiaa.org/doi/epdf/10.2514/1.A36143
Jan 15, 2025—New paper published in Biogeosciences titled, "Ensemble estimates of global wetland methane emissions over 2000–2020", and was led by Zhen Zhang at the University of Maryland with George and Ryan Riggs contributing as coauthors. This study is one of the outcomes of the RECCAP2 Wetlands Working Group and is the first comprehensive evaluation and attribution of recent changes in methane emissions from wetlands. https://doi.org/10.5194/bg-22-305-2025
Jan 1, 2025—Paper published in Journal of Hydrology titled, "Meteorological Drivers and the Trend of Daily Extreme Reservoir Evaporation Events in the Western United States", led by Bingjie Zhao, now at Brown University. Among other results, this study finds that extremely high evaporation events occur over lakes during times of high wind speeds. https://doi.org/10.1016/j.jhydrol.2024.132589
Dec 20, 2024—Grant funded! NASA Advanced Information Systems Technology (AIST) proposal selected for funding entiteld "3D-CHESS FO: Autonomous Sensor Web for Inland Water Ecosystem Monitoring". Led by Dani Selva at Texas A&M University, George will serve as VT Co-I/Institutional PI with Quinn Thomas, Cayelan Carey, and Shaddi Hasan as VT Co-Is. https://esto.nasa.gov/project-selections-for-aist23/#Selva
Dec 17, 2024—George is quoted in a NASA-JPL News article on SWOT and the Ohio River Basin: https://www.jpl.nasa.gov/news/cutting-edge-satellite-tracks-lake-water-levels-in-ohio-river-basin/
Dec 9-13, 2024—Katie, Emily, Molly, Yohtaro, Hana, Luisana and George all travel to Washington D.C. to present their research and network at the AGU Annual Conference. We also met up with former group mates Ryan Riggs, John Morgan, and Carter Boyd.