What We Saw from Satellite-Retrieved Snow Cover Data
We took a closer look at the snow conditions during the last holiday season to find out which areas had white Christmas. For the analysis we used a high-quality snow cover dataset and the Planet OS API.
It’s not only the people that await for the snow during wintertime. Seasonal snow is a very important part of our planet’s climate system. It helps regulate the temperature of the Earth’s surface and maintain a healthy energy balance. Water from the melting snow is crucial for rivers and reservoirs in many regions of the world. Snow can also affect the arrival of the summer monsoon season and influence how long it will last.
Each year before the holiday season, snow becomes the topic of conversation among people in the Northern regions as they start discussing whether there will be white Christmas this year. We wanted to know how successful was this December, so we added a high-quality snow cover dataset to the Planet OS Datahub and analyzed the snow conditions during Christmas.
The National Snow & Ice Data Center (NSIDC) satellite-retrieved snow cover dataset provides daily observational data. It reports the percentage of snow-covered land in 0.05° (approx. 5 km) resolution Climate Modeling Grid cells. Percentages are computed from snow cover observations in the MODIS/Terra Snow Cover Daily L3 Global 500m Grid dataset. Cloud cover percentages are also provided.
The main variable in my analysis about snow cover on December 24th in the Northern Hemisphere is Daily snow extent. As MODIS uses visible light from Earth, the data is not collected during the night. Also note that the clouds influence the results. Below you will find the highlights from the analysis.
Here are some of the things I discovered:
- Canada had plenty of snow on December 24th, as did some of the places in North America, mostly in the mountains. The news outlets even reported that the Canada’s biggest airport suffered long delays due to the heavy snowfall.
- It was also snowy in Seattle, where according to the local news Christmas in the past five years had been without snow.
- People in Europe didn’t get much snow except for the ones living in the Alps and some parts of Norway, Sweden, Finland and Estonia.
- Some countries in the eastern part of the world, for example Russia, China and Mongolia, also had snow.
- In the video above we took a closer look at the Alps and discovered that the mountains were almost entirely covered in snow while the flat land appeared snowless. You can use the interactive map from my analysis to zoom in the other parts of the world.
As you can see, the areas in latitudes higher than ~62N have no data. It’s because MODIS instrument requires sunlight to operate (it’s like a digital camera in many respects). During Christmas most of that region has a Polar Night or very little daylight. Hence the lack of data.
For more detailed examples of how you can use the Planet OS Datahub API to work with snow cover data, check out my Jupyter notebook on GitHub. Happy 2018, everyone!