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Site characteristics: Soil moisture summary for 376 SNOTEL station locations

Detre, Ally1; McGrath, Daniel1

Research facility: Colorado State University
Published Aug 13, 2025 on Dryad. https://doi.org/10.5061/dryad.bvq83bkm9

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Abstract

Satellite-based synthetic aperture radar (SAR) has been used to assess and quantify snowmelt across large spatial and temporal scales. While there have been recent advancements in SAR-based snow water equivalent (SWE) retrieval methods, obtaining accurate estimates of SWE requires knowledge of the amount of liquid water content in the snowpack given its strong impact on radar velocity. Recent studies have utilized Sentinel-1 SAR to identify snowmelt runoff onset in complex, high-elevation terrain based on a seasonal minimum backscatter time-series, however, detailed investigations into the snowpack state before and after snowmelt runoff onset are lacking. In this study, we integrated repeat field measurements, SNOw TELemetry (SNOTEL) station data (n = 260) from across the western U.S., and paired Sentinel-1 SAR estimates of snowmelt runoff onset to 1) assess the snowpack state prior to and after Sentinel-1 SAR-derived runoff onset estimates, and 2) evaluate Sentinel-1 SAR estimates of runoff onset with SNOTEL-derived estimates of melt output via soil moisture “pulses”. We found that SNOTEL soil moisture pulses preceded Sentinel-1 SAR estimates of snowmelt runoff onset by a median of 3 days (standard deviation = ± 25.3 days) and post-dated peak SWE by a median of 3 days (standard deviation = ± 18.2 days). Soil moisture pulse dates occurred earliest in montane forests/prairie snowpacks and latest in maritime snowpacks. Snow density and number of positive degree days on soil moisture pulse date increased with latitude and longitude and decreased with elevation. While satellite-based estimates of snowmelt runoff onset provide a promising methodology for improving spaceborne retrievals of SWE, we emphasize the importance and influence of local climatological conditions on runoff onset signal clarity for both in-situ and satellite-based estimates.