I want to calculate growing degree days.

I have hourly data of temperature between the hours of 00:00 and 23:59.

I want to calculate the growing degree days and I saw that I need the minimum,maximum and mean temperatures. However, I don't know if I should filter my data to contain temperature data only for the daylight time or to use the whole day temperature.

What is the right data to use for the GDD calcualtion?


1 Answer 1


I have no actual familiarity myself with implementing growing degree days itself.

That said, in reading through some references like (1), (2), and (3) I see no indication that it should be filtered.

The terminology also sounds to stem from the longer used heating degree day and cooling degree day, which I know is done from just the max and min over the 24 hour day (as this NOAA page suggests).

And in addition, the lowest temperature of the day usually occurs right near or just after dawn, so filtering it to "daytime" temperatures being when the sun is up would basically include roughly the coldest (and hottest) temperature of the day anyways.

So while I've never interacted with this specific metric, everything suggests to me that you would just use the values over a standard 24 hour day.

  • $\begingroup$ Actually, I eventually was able to find official references to explicitly state it as midnight to midnight. Just have to come up with the right Google search term... putting a word in quotes requires it to be found and helps, so I used < growing degree days "midnight" > and found this general page from the University of North Dakota that suggests midnight to midnight... $\endgroup$ May 2, 2022 at 14:01
  • $\begingroup$ ... and this writeup from some of the people there that says "Growing degree-days (GDD) wer calculated for each 24-hour period, midnight to midnight, from daily maximum (Tmax) and minimum (Tmin) air temperature measured hourly in degrees Fahrenheit at the 2-meter height (about 6.5 feet) at each site.", so it looks the midnight to midnight method is confirmed $\endgroup$ May 2, 2022 at 14:02

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