The value of long-term (40 years) airborne gamma radiation SWE record: Evaluating CONUS SWE datasets by seasonal snow and land cover classifications

Reliable long-term snow water equivalent (SWE) measurements are needed for effective water management and flood risk assessments under changing climate. Several long-term SWE products have been developed by using satellite radiometers or/and assimilation techniques by ingesting ground-based snow station networks. To date, an evaluation of the currently available SWE products has been challenged due to the lack of independent SWE data at a continental scale. In this study, the historical airborne gamma radiation SWE observations (20,738 measurements) operated by the National Oceanic and Atmospheric Administration's Office of Water Prediction (NOAA OWP; and formerly by the National Operational Hydrologic Remote Sensing Center) are used to evaluate three observation-based long-term SWE products, spaceborne passive microwave SWE derived from the series of the Special Sensor Microwave Imager and Sounder (SSMI/S), GlobSnow-2 SWE, and University of Arizona (UA) SWE by seasonal snow cover and land cover classifications over the continental United States (CONUS) from 1982 to 2017. As compared to SSMI/S and GlobSnow-2 SWE, UA SWE has much better agreement with gamma SWE across all land cover types and snow classes. The results demonstrate the reliability of the UA SWE products as well as the benefits of the gamma radiation approach to measure SWE, especially in forested regions. As an operational, independent long-term SWE record, the NOAA airborne gamma SWE dataset is widely applicable not only to improve the capability of snowmelt flood prediction as an operational purpose, but also to evaluate the modeled SWE from land surface and regional climate models, and reanalysis schemes.