| Abstrakt: |
Observation‐based long‐term gridded snow water equivalent (SWE) products are important assets for hydrological and climate research. However, an evaluation of the currently available SWE products has been limited due to the lack of independent SWE data that extend over a large range of environmental conditions. In this study, three daily long‐term SWE products (Special Sensor Microwave Imager and Sounder [SSMI/S] SWE, GlobSnow‐2 SWE, and University of Arizona [UA] SWE) were evaluated by seasonal snow cover and land cover classifications over the conterminous United States from 1982 to 2017, using the historical airborne gamma radiation SWE observations (20,738 measurements). We found that there are similar patterns in SSMI/S and GlobSnow‐2 SWE when compared against the gamma SWE. However, GlobSnow‐2 SWE had better agreement with gamma SWE than SSMI/S SWE in some forested‐type classes and maritime and prairie snow classes. As compared to SSMI/S and GlobSnow‐2 SWE, UA SWE has much better agreement with gamma SWE in all land cover types and snow classes. Tree cover and topographic heterogeneity affect the agreement between the gamma and gridded SWE and accuracy of gamma SWE itself with the largest differences typically occurring when the percent tree cover was 80% or higher, the terrain slope was steeper than 2.5°, and the elevation range exceeded 100 m. The results demonstrate the reliability of the UA SWE products and the benefits of the gamma radiation approach to measure SWE, especially in forested regions. Plain Language Summary: Long‐term gridded snowpack data are essential for effective water resource management and flood risk assessments under a changing climate in the United States. However, the currently available snowpack data have large uncertainties, and the evaluations have been limited due to the lack of reliable independent data sets. Here, we evaluate three daily long‐term (>30 years) snow water equivalent (SWE) products—empirically based SWE from passive microwave, GlobSnow‐2 SWE, and University of Arizona SWE from 1982 to 2017 over the conterminous United States—using the historical airborne gamma SWE observations collected by the National Oceanic and Atmospheric Administration. Two key findings are that (1) the UA SWE product is the most reliable and (2) the long‐term airborne SWE record is of great value, especially in forested regions. Key Points: Long‐term airborne gamma radiation observations provide reliable SWE observations even over forest regionsUniversity of Arizona (UA) SWE has the strongest agreement with gamma SWE regardless of seasonal snow and land cover classLarge differences occur when the tree cover is 80% or higher, the slope is steeper than 2.5°, and the elevation range exceeds 100 m [ABSTRACT FROM AUTHOR] |
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