mcrossley wrote: ↑Mon 19 Apr 2021 9:52 am
OK, my view...
The argument between integrated and max+min / 2 methods for calculating the GDD is a bit moot. I calculated using both methods going back over all my data (5 minute intervals).
Most years the difference using a 5C base temp was around 10 GDD (either way) out of a total of ~ 1500 - 2000. Around 0.5%, so not really worth arguing about when most of the GDD "ranges" I have seen for growth events are at least an order of magnitude or two greater.
I do note that the integral method does seem count days earlier in the season than the max/min method - maybe using the integral method would allow them to refine the ranges? Though I suspect it is much more complex than that, and sunshine hours and soil moisture also need to be factored in to create a "growth index". Anyone up for that?!
I intend to implement the max+min / 2 method
Variant A , there a few reasons for this...
- Using the integral method is computationally expensive to perform retrospectively and you lose the minute by minute data, which means that the GDD really has to be recorded daily into the dayfile. This means extending the MySQL schema, and the ExportToMySQL and CreateMissing utilities. This is not something I wish to do.
- The max+min / 2 method is simple enough to to implement on the fly, so no extension to the dayfile required
- Calculating GDD on the fly means the base temperature can easily be amended for different crops
I intend to implement the ability to show two different GDD series which can have different base temperatures. The data selection gets a bit messy with lots of years of data, but I see this is a tool for farmers and horticulturists not a casual click and scan visitor. Maybe someone can come up with good way of handling lots of data series in HighCharts.
Thermal growing season:
To determine the beginning of the thermal growing season:
The thermal growing season begins when the snow has melted from open places and the average daily temperature rises permanently above +5 degrees. As the average daily temperature in the spring can vary for a long time on both sides of +5 degrees, the situation is monitored for 10 days.
End of thermal growth season:
In autumn, the thermal growing season ends when the average daily temperature drops permanently below +5 degrees or a permanent snow cover is obtained. In autumn, even severe night frosts interrupt the growing season for several nights in a row.
Monitoring of the thermal growth season using the sum of the effective temperature:
The unit of the effective temperature sum is the degree of day in ° Cvrk. The amount is accrued for days when the average daily temperature is above +5 degrees. The sum includes the part of the daily average temperature exceeding five degrees during the growing season. If the average daily temperature during the growing season is below + 5 degrees, the amount is not accumulated, but it is not reduced either. The growing season is then considered to have stopped temporarily.
Daily value of air temperature (average daily temperature):
From 1959 onwards, the daily mean temperature values (ºC) are calculated from the instantaneous temperature value at the eight observation times of the day (00,03,06,09,12, 15,18 and 21 UTC). If not all eight temperature values are available, then the average can be calculated using the four temperature values and the 12-hour extremes (minimum and maximum temperatures) measured in the morning (6 UTC) and evening (18 UTC), depending on the missing observation time.
Previous data copied from the Finnish Meteorological Institute (FMI) page.
There is no mention of the +30 degree limit on the FMI website.
At my weather station over 10 years, maximum average temperatures range from +20 to +25 degrees (+25 degrees for a total of five days)
But you have to think about it globally, so you may have to use the +30 degree limit as well.
The Degree Days and Temp Sum Graphics look great. My graphics have been implemented according to the average of the NOAA calculated by cmx so it's good to see what is the difference between the actual calculation method.
