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