Benchmarking Snow Fields of ERA5-Land in the Northern Regions of North America
Bibliographic record
Abstract
Abstract. Reanalysis products provide new opportunities for assessments of historical Earth System states. This is crucial for snow variables, where ground-based observations are sparse and incomplete, and remote sensing measurements still face limitation. However, because reanalysis data are model-based, their accuracy must be evaluated before being applied in impact and attribution studies. In this study, we assess the accuracy of ERA5-Land's snow cover, snow depth, and Snow Water Equivalent (SWE) across monthly, seasonal, and annual scales, within the ecological regions of Canada and Alaska, regions that are characterized by prolonged seasonal snow cover. Using MODIS satellite snow cover observations and the gridded snow depth/SWE analysis data from the Canadian Meteorological Centre, we conduct a consistent benchmarking of ERA5-Land’s snow fields to (1) identify discrepancies at both gridded and regional scales, (2) evaluate the reproducibility of spatial structure of snow variables, and (3) uncover potential spatial patterns of discrepancies in ERA5-Land's snow statistics. Our results highlight significant discrepancies, particularly for snow depth and SWE, where ERA5-Land tends to grossly overestimate long-term mean values and interannual variability, while underestimating trends, i.e., moderating positive trends and exaggerating negative ones. The discrepancies in SWE, however, are primarily driven by biases in snow depth rather than snow density. Therefore, we advise against the direct use of ERA5-Land's snow depth and SWE in Canada and Alaska. While snow cover and snow density may still be useful for impact and attribution studies, they should be applied with caution and potential bias corrections particularly at local and smaller scales.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".