Calculating Degree Days
Ashley FontNational Science Foundation Graduate STEM Fellow in K-12
EducationSugar Creek Watershed K-12 Education Program
The Ohio State University-Ohio Agricultural Research and Development Center
The Degree Day
FIRST OF ALL! Degree DAY is not a literal DAY
It is just CALLED a Degree DAY
The Degree Day
Unit of Heat
Average amount of heat in degrees that have occurred in a single day
1 Degree Day results when the Average daily temperature is 1 degree above the lower threshold EX: Average 51 degrees, threshold is
50 degrees… 51-50= 1 dd
What is a lower threshold?
Just means the lowest temperature that something can grow at.
Some insects cannot develop until the temperature is 50°F Any lower, and the bug stops growing!
Therefore, 50°F would be that bug’s threshold
Why do we use it?
Monitoring these values of heat can help us predict pest activity
Since insects are cold blooded, daily temperatures have A LOT to do with their development
Temperature can be more precise than just using calendar dates.
Calculations
Use the daily maximum temperature and the daily minimum temperature
Get an Average for the day
Subtract a lower threshold (we use 50F unless otherwise instructed)
The Formula
(Max. Daily Temp. + Min. Daily Temp.) __ Lower
2 Threshold
Examples (pg 2)
#1June 1st, 2008
MAX: 74.1°F MIN: 50.2°F Lower Threshold: 50°F
Calculation (74.1 + 50.2 ) - 50 = 12.15 2
So, on June 1st, 12.15 Degree Days have accumulated
Examples cont. (pg 2)# 2 When the minimum daily temperature is
BELOW the lower threshold, REPLACE the Minimum Daily Temp in the formula with the THRESHOLD.**
May 28th,2008 MAX: 66.5°F MIN: 38.6°F LT: 50°F
( 66.5 + 50 ) - 50 = 8.25 2
Examples cont. (pg 2)#3** There are not NEGATIVE degree days. If
the formula results in a negative, it is ZERO degree days… meaning no heat accumulated on this day
January 1st Max:41.6 Min:19.0 LT: 50°F (41.6 + 50) - 50 = -4.2 2 So, ZERO DD. No development occurred this day.
Cumulative Degree Day
Just adding up each day’s DD units to get the total for multiple days
Usually start adding at January 1st.
This can help us predict what day of the year something will occur by following how much heat is accumulated each day.
Assignments
Do in class In pairs Use Calculators
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