Buarque et al. (2025) Insights into the North Hemisphere daily snowpack at high resolution from the new Crocus–ERA5 product

Identification

• Journal: Earth system science data
• Year: 2025
• Date: 2025-12-17
• Authors: Silvana Ramos Buarque, Bertrand Decharme, Alina Barbu, L. Franchistéguy
• DOI: 10.5194/essd-17-7227-2025

Research Groups

• Météo-France, CNRS, Univ. Toulouse, CNRM, Toulouse, France
• Météo-France, Direction des Systèmes d’Observation, Toulouse, France

Short Summary

This study introduces and evaluates the new daily Crocus–ERA5 snow product for the Northern Hemisphere (1950–2022), demonstrating its improved accuracy in snow depth and cover compared to its predecessor, Crocus-ERA-Interim, particularly in Eurasia, despite persistent biases in some Arctic regions.

Objective

• To provide a brief evaluation and insight into the Crocus–ERA5 daily snow product, which uses improved ERA5 atmospheric forcing for enhanced accuracy, offers comprehensive documentation of its strengths and limitations, and is validated against independent in-situ observations and multi-source satellite data.

Study Configuration

• Spatial Scale: Northern Hemisphere, with a focus on Arctic regions (latitudes > 60° N) including North America and Eurasia. The Crocus–ERA5 product is at 0.25° resolution.
• Temporal Scale: The Crocus–ERA5 product covers 1 July 1950 to 30 June 2023. Evaluation periods include 1979–2018 (comparison with Crocus-ERA-Interim), 1950–2012 (in-situ observations), and 2000–2022 (IMS satellite data).

Methodology and Data

• Models used:
  • Crocus multi-layer snow model (simulates snow albedo, heat transfer, phase change, mass, density, grain metamorphism).
  • ISBA (Interactions between Soil–Biosphere–Atmosphere) land surface model.
  • SURFEX numerical platform (couples Crocus with other surface components).
• Data sources:
  • Atmospheric Forcing: ERA5 global atmospheric reanalysis (European Centre for Medium-Range Weather Forecasts - ECMWF).
  • Comparison Forcing: ERA-Interim global atmospheric reanalysis.
  • In-situ Observations: Harmonized dataset of over 2000 stations with daily snow depth measurements across North America and Eurasia (1950–2012).
  • Satellite Data: Interactive Multisensor Snow and Ice Mapping System (IMS) satellite data (NOAA AVHRR, MODIS, VIIRS, Sentinel satellites, in-situ observations, NCEP model data) for snow cover extent (2000–2022) at 24 km resolution.

Main Results

• Crocus–ERA5, driven by ERA5 reanalysis (0.25° resolution), shows improved snowpack estimates compared to Crocus-ERA-Interim (0.75° resolution), particularly in spring over Eurasia.
• In Eurasia, Crocus–ERA5 exhibits a systematic shift towards higher mean snow depth (e.g., 15% in April, 26% in May) and greater variability (e.g., 15% in April, 24% in May) compared to Crocus-ERA-Interim. In North America, increases are smaller (8% mean, 7% variability in April; 16% mean, 10% variability in May).
• Crocus–ERA5 generally reproduces the spatial distribution of snow depth across the Northern Hemisphere but tends to overestimate it, with over 60% of biases falling between 0.05 m and 0.1 m.
• The model shows good agreement with in-situ observations for the annual snow cycle, with high correlations (R > 0.8) for most snow depth-related variables, and particularly strong correlations (R ≥ 0.96) for the number of days with snow and duration of continuous snow cover.
• Crocus–ERA5 simulates a slightly shorter snow season in the Arctic and a longer one in sub-Arctic plains, with biases typically around ±2 days.
• Comparison with IMS satellite data for snow cover extent (SCE) shows a correlation of 0.72. Crocus–ERA5 exhibits a steeper downward trend in Northern Hemisphere SCF (slope of -1.9 × 10^-12) compared to IMS (slope of -4.5 × 10^-13) from 2000 to 2022.
• Biases in SCF exist: Crocus–ERA5 shows positive biases in mountainous regions south of 60° N and tends to melt snow more rapidly than IMS in northern western Canada, southern eastern Canada, and eastern Siberia, partly due to its idealized open-field (grassland) surface representation and lack of snow-forest interaction modeling.

Contributions

• Provides the first comprehensive overview and evaluation of the new Crocus–ERA5 daily snow product, highlighting its advancements over previous versions.
• Documents the strengths and limitations of Crocus–ERA5 for snow depth and snow cover, validated against extensive independent in-situ and satellite datasets.
• Offers a freely available, high-resolution (0.25°) daily snow product for the Northern Hemisphere (1950–2023), crucial for continental cryosphere and climate change studies.
• Demonstrates the impact of improved atmospheric forcing (ERA5) on snowpack simulations, showing enhanced accuracy, particularly in interannual variability and seasonal cycles.

Funding

The production of this snow dataset responds to requests from the continental cryosphere community, with involvement from French and Canadian government institutions (CNRM and ECCC) in monitoring Arctic snow cover for the Arctic Report Card. No specific project or program reference codes are listed as direct funding for this research.

Citation

@article{Buarque2025Insights,
  author = {Buarque, Silvana Ramos and Decharme, Bertrand and Barbu, Alina and Franchistéguy, L.},
  title = {Insights into the North Hemisphere daily snowpack at high resolution from the new Crocus–ERA5 product},
  journal = {Earth system science data},
  year = {2025},
  doi = {10.5194/essd-17-7227-2025},
  url = {https://doi.org/10.5194/essd-17-7227-2025}
}