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NEW MEXICO
CLIMATE CENTER
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Computation of Heat Units and
Degree Days
Using the Averaging Method
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Growing Degree Days equation
| List of Symbols Used |
| Name |
Value |
Units |
Description |
| maxtemp |
|
degree C or F |
maximum daily air temperatureat 1.5
meter heigh |
| mintemp |
|
degree C or F |
minimum daily air temperature at 1.5
meter height |
| basetemp |
|
degree C or F |
Base temperature unique for each plant
type or insect life cycle F or C |
| maxcutoff |
|
degree C or F |
maximum cutoff temperature when
temperature exceeds value set to maxcutoff |
| mincutoff |
|
degree C or F |
minimum cutoff temperature when
temperature less than value set to mincutoff |
Equation for Growing Degree Days:
Gdd= (maxtemp+mintemp)/2 -basetemp
set maxtemp to maxcutoff if maxtemp greater than maxcutoff
set mintemp to mincutoff if mintemp less than mincutoff
Heating degree days are sometimes calculated as:
- (maxtemp+mintemp)/2 - basetemp
where no cutoff temperatures are used. If you want these degree days
then use 999 for the maximum cutoff and -999 for the minimum.
Degree days are also calculated using a sine function fit through the
maximum and minimum temperature and then the area above a base temperature
determined by integration. This is the method used by California and Arizona
and results in different gdd than the averaging method described above.
For a complete description of the sine curve method read:
- University of California leaflet 21373
Degree-Days: The Calculation and Use of Heat Units in
Pest management (1983).
Another description of the sine curve method of calculating degree days
is presented by Snyder (1985)
References:
Gilmore, E. C. Jr. and J. S. Rogers. 1958. Heat units as a method of
measuring maturity in corn. Agronomy Journal 50:611-615
Snyder, R.L. 1985. Hand Calculating Degree Days
Agricultural and Forest Meterology, 35:353-358
| Created: |
29 Apr 1996 |
| Updated: |
1 May 1996 |
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