Armstrong Professor Colin Gleason of the Civil and Environmental Engineering (CEE) Department was one of two senior authors on an article named by the respected journal Water Resources Research as one of its five most-read papers in 2023. The groundbreaking paper, “A Framework for Estimating Global River Discharge from [NASA’s] Surface Water and Ocean Topography Satellite [SWOT] Mission,” was first published in Water Resources Research – or what Gleason calls “the world’s best hydrology journal” – on March 27, 2023. 

In addition to co-authoring the Water Resources Research paper, Gleason serves as the Lead Academic Scientist for Calibration and Validation of U.S. Inland Hydrology for the SWOT satellite and is also a member of the SWOT Science Team.

SWOT is a collaboration among the space agencies of the United States, France, United Kingdom, and Canada and was designed to measure the Earth’s oceans and surface water. The SWOT satellite was launched on December 15, 2022, and was engineered to produce estimates of “river discharge” (or the volume of water flowing through a river channel) on many rivers where no on-site discharge measurements are currently available. Thus, the mission will significantly boost the observational basis for understanding global hydrological processes. 

According to the landmark Water Resources Research paper, a magnum opus written by more than 35 authors, “The SWOT mission will vastly expand measurements of global rivers, providing critical new data sets for both gauged and ungauged basins.”

The authors expect that SWOT data, expected to be available in the first half of 2024, will provide discharge for all rivers on Earth wider than 100 meters. Until now, however, a full exploration of the SWOT discharge philosophy, methodology, and expected uncertainty has not been presented in the literature. That’s precisely what the Water Resources Research paper does.

As the authors explain, “Measurements of river discharge integrate upstream water-cycle processes and thus are among our most-important data resources for understanding hydrology from the watershed to continental scales. However, most of the world's rivers are functionally ungauged due to a range of factors, including lack of resources and lack of data sharing.” 

As the paper notes, “Remote sensing of river discharge provides the possibility of global observation even in ungauged basins, but with important tradeoffs, including decreased measurement accuracy, precision, and sampling frequency as compared with observing discharge in situ.”

The Water Resources Research paper documents those tradeoffs, both good and bad. In this paper, as the authors explain, “We present for the first time a complete estimate of the SWOT discharge uncertainty budget, with separate terms for random (standard error) and systematic (bias) uncertainty components in river-discharge time series.”

According to the authors, “We expect that discharge uncertainty will be less than 30 percent for two-thirds of global reaches and will be dominated by a systematic bias. Temporal variations in river-discharge time series are expected to be estimated within 15 percent for nearly all reaches, thus capturing the response of river discharge to rainfall and snowmelt events, including in basins that are currently ungauged, and providing a new capability for scientists to better track the flows of freshwater through the Earth system.”

The authors conclude that “We believe this level of accuracy lays the groundwork for SWOT to enable breakthroughs in global hydrologic science.” 

Gleason’s lab in the CEE department focuses on translating process-based hydrology and geochemistry to global scales through extensive Arctic fieldwork, satellite data processing, and geomorphic-informed modelling and data assimilation. Among other honors, Gleason is a National Science Foundation CAREER awardee, a NASA New Investigator, and a member of the Science Team for NASA’s High Mountain Asia program. (February 2024)

Article posted in Research