References

Growing degree days

We calculated growing degree days for the cover crops in the Green Covr project using data from the Midwestern Regional Climate Center and their Climate Data Access Portal API. The latitude and longitude of each Green Covr collection was used to find the nearest climate station. Stations searched included those in Iowa, Minnesota, North Dakota, South Dakota, and Wisconsin. Hourly data for average air temperature was downloaded from the nearest station. If the nearest station had no temperature data or was missing more than 5% of the hourly records then this station was discarded and the next nearest station was used.

The average temperature for each day was calculated from hourly records. The difference between the average temperature for each day and the base temperature was taken. The base temperature used in calculating the growing degree days was 40 degrees Fahrenheit and the upper threshold was set to 86. If a daily average exceeded 86 degrees then it was set to 86, and if the daily average was below 40, then no growing degree days were accumulated. The calculated growing degree days for each day were summed to provide a cumulative growing degree day value for the collection point.

Green canopy image analysis

This project was inspired by the work of Patrignani and Ochsner (2015) with code adapted by Dr. Melissa Wilson's lab from Patrignani and Oschner (2015). Default values given by Patrignani and Oschner (2015) were used for the green cover calculation.