Assessing the potential for the Surface Water and Ocean Topography (SWOT) mission for constituent flux estimations

The recently launched Surface Water and Ocean Topography (SWOT) satellite will simultaneously measure river surface water widths, elevations, and slopes. These novel observations combined with assumptions for unobserved bathymetry and roughness enable the derivation of river discharge. Derived discharge data will not be available until the fall of 2023, despite the satellite having completed approximately 6 months of observations for validation and calibration and transitioning into the nominal orbit phase. SWOT has an irregular flyover frequency, ranging from roughly 1 to 10 times per 21 days. Here, we present how best to use SWOT data when it becomes live, including consideration of how best to accommodate or utilize the irregular flyover frequency of SWOT as it intersects with river reaches. We investigate the predicted capabilities of SWOT for several major rivers using synthetic/theoretical SWOT time series data and evaluate how the characteristics of river discharge dynamics and SWOT sampling frequency impact discharge estimates. This analysis indicates the irregular frequency of SWOT best captures the hydrology of larger, more stable, rivers but presents challenges in smaller, flashier rivers, particularly when sampling frequency decreases (i.e., falls to once per 21 days). Further, the use of SWOT discharge for quantifying constituent fluxes is considered. We provide recommendations concerning how to best use SWOT data for applications related to hydrology and biogeochemistry, including how to design studies to accommodate its irregular orbit cycle

Groundwater isotopes across scales: continent-wide modeling and local field characterization

Groundwater is one of the world\u27s most important natural resources. The use of stable water isotopes (ð›¿2H and ð›¿18O) as natural tracers through the water cycle has provided a unique observational technique for characterizing hydrological processes and establishing connections between water distribution systems and their respective environmental sources. A predictive model for groundwater isotopes was developed across the contiguous United States (to combat pre-existing limitations of the lack of such data) using a random forest model based on environmental parameters. We find evident spatial coherence in the model, generally mirroring the signal of isotopes of precipitation, and highlight the potential for its application across hydrology and ecology. In addition, to demonstrate the applicability and versatility of groundwater isotopes, we investigated the local municipal water supply in Schenectady to understand the sources and seasonal variability in these sources. The Schenectady municipal well-field is sited less than a kilometer from the Mohawk River, making the interaction between surface water and groundwater highly complex and seasonally dependent. Schenectady tap water, which is drawn from local groundwater, and Mohawk River water were collected at regular intervals and analyzed in the Union College Stable Isotope Laboratory for stable isotopes of hydrogen and oxygen. The seasonal signal of isotopes can be approximated by sine waves, and the phase and amplitude of these signals can be used to calculate the average linear velocity (3.5 m/day) of the water moving into the aquifer and fraction of young water (57% \u3c 2.7 months) in the local groundwater. Our results highlight the connection between the Mohawk River and the aquifer in the vicinity of the Schenectady well-field, and motivates further research to characterize the potential for vulnerabilities. Thus, this study not only provides an isoscape to detail the spatial distribution of isotopes regionally, but also demonstrates how we can leverage our understanding of isotopes for insight into the chemical and physical hydrology in a local water system

Deriving River Discharge Using Remotely Sensed Water Surface Characteristics and Satellite Altimetry in the Mississippi River Basin

River discharges are critical for understanding hydrologic and ecological systems, yet in situ data are limited in many regions of the world. While approximating river discharge using satellite-derived water surface characteristics is possible, the key challenges are unknown channel bathymetry and roughness. Here, we present an application for merging mean river-reach characteristics and time-varying altimetry measurements to estimate river discharge for sites within the Mississippi River Basin (USA). This project leverages the Surface Water and Ocean Topography (SWOT) River Database (SWORD) for approximating mean river-reach widths and slopes and altimetry data from JASON-2/3 (2008–Present) and Sentinel-3A/B (2015–Present) obtained from the Hydroweb Theia virtual stations. River discharge is calculated using Manning’s Equation, with optimized parameters for surface roughness, bottom elevation, and channel shape determined using the Kling–Gupta Efficiency (KGE). The results of this study indicate the use of optimized characteristics return 87% of sites with KGE > −0.41, which indicates that the approach provides discharges that outperform using the mean discharge. The use of precipitation to approximate missing flows not observed by satellites results in 66% of sites with KGE > −0.41, while the use of TWSA results in 65% of sites with KGE > −0.41. Future research will focus on extending this application for all available sites in the United States, as well as trying to understand how climate and landscape factors (e.g., precipitation, temperature, soil moisture, landcover) relate to river and watershed characteristics

Deriving River Discharge Using Remotely Sensed Water Surface Characteristics and Satellite Altimetry in the Mississippi River Basin

River discharges are critical for understanding hydrologic and ecological systems, yet in situ data are limited in many regions of the world. While approximating river discharge using satellite-derived water surface characteristics is possible, the key challenges are unknown channel bathymetry and roughness. Here, we present an application for merging mean river-reach characteristics and time-varying altimetry measurements to estimate river discharge for sites within the Mississippi River Basin (USA). This project leverages the Surface Water and Ocean Topography (SWOT) River Database (SWORD) for approximating mean river-reach widths and slopes and altimetry data from JASON-2/3 (2008–Present) and Sentinel-3A/B (2015–Present) obtained from the Hydroweb Theia virtual stations. River discharge is calculated using Manning’s Equation, with optimized parameters for surface roughness, bottom elevation, and channel shape determined using the Kling–Gupta Efficiency (KGE). The results of this study indicate the use of optimized characteristics return 87% of sites with KGE > −0.41, which indicates that the approach provides discharges that outperform using the mean discharge. The use of precipitation to approximate missing flows not observed by satellites results in 66% of sites with KGE > −0.41, while the use of TWSA results in 65% of sites with KGE > −0.41. Future research will focus on extending this application for all available sites in the United States, as well as trying to understand how climate and landscape factors (e.g., precipitation, temperature, soil moisture, landcover) relate to river and watershed characteristics