This app shows the snow cover duration anomaly of the current snow season in comparison with the average snow cover duration over the same period of the year between 2000-2021. The snow cover is obtained from Nasa’s Terra/MODIS satellite observations. The app is automatically updated when new observations are available. Click here to view in full screen.

New: we provide here an experimental application which shows the current snow cover area in comparison with a 30-year climatology that was generated by machine learning from the UERRA reanalysis (documentation under preparation). The plots will appear below after a 1 minute load time. You can select the entire Alps or a river basin subregion.

Method

  • The daily NDSI is extracted from the MOD10A1.006 collection (~500 m spatial resolution). Missing values are filled using a linear interpolation in the time dimension [1].
  • The resulting series of daily gap-free NDSI is converted to a series of binary snow maps (snow / no-snow) using the threshold NDSI>0.2.
  • The snow duration is the sum of the snow maps along the time axis.
  • The snow maps over 2000-2021 were pre-computed and stored as an asset to reduce the app loading time (but it’s still slow).

[1] Although more sophisticated algorithms exist to fill gaps in MODIS snow cover maps, the linear interpolation in the time dimension is a good trade-off between efficiency and accuracy (Gascoin et al. 2015).