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Calculating Degree Days Ashley Font National Science Foundation Graduate STEM Fellow in K-12 Education Sugar Creek Watershed K-12 Education Program The Ohio State University-Ohio Agricultural Research and Development Center

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The Degree Day FIRST OF ALL! Degree DAY is not a literal DAY It is just CALLED a Degree DAY

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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

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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

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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.

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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)

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The Formula (Max. Daily Temp. + Min. Daily Temp.) __ Lower 2 Threshold

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Examples (pg 2) #1 June 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

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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

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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 1 st Max:41.6 Min:19.0 LT: 50°F (41.6 + 50) - 50 = -4.2 2 So, ZERO DD. No development occurred this day.

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Cumulative Degree Day Just adding up each day’s DD units to get the total for multiple days Usually start adding at January 1 st. This can help us predict what day of the year something will occur by following how much heat is accumulated each day.

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Assignments Do in class In pairs Use Calculators

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