How to Calculate Wheat GDD and Determine When Greenup Occurs

March 16, 2022

This tutorial shows users how to access the Michigan Automated Weather Network data and calculate growing degree days (GDD) for wheat. Wheat uses Celsius degrees, method is a simple average and base temperature is zero.

Video Transcript
[Music]
hello this is dennis pennington wheat
extension specialist for michigan state
university here to show you today how to
download weather data and calculate
growing degree days for wheat and
determine whether you've reached green
up or not
so first
go to the msu enviro weather
station or website it's at
enviroweather.msu.edu
i'll type that into the the box here
in the recording
once you get to enviro weather there's a
bunch of different
menus across the top if you go to
weather come down here to the bottom
there's this thing called data on demand
you're going to want to click on data on
demand it's down here at the bottom
and then you'll be able to download data
specifically for what you want they have
a bunch of other tools and information
that you can access here and you can
play around with those um to see what
they are
but in order to download this data we're
going to need to go to this data on
demand so i'll click on that and it
takes me up
to this station or this page and this is
the map that shows where all the
different weather stations are located
so find a weather station that's located
nearest to you
i'm going to just pick east lansing
because i'm in east lansing
when i get there it's got a picture of
the the weather station and where it's
located it tells you some information
about it the lat lawn
locations and the elevation so on and if
you scroll on down here
you can get these custom reports this is
what you want you want this this is the
data on demand and if you hit the drop
down arrow here you want to go down to
growing degree day
data um there's a bunch of other things
that you can get here as well but for
these calculations we wanted the growing
degree data once you do that notice now
we have uh these selections down here to
make
first thing is you got to select what
method well we do not use the
baskerville min we use the simple
average and our base temperature is
going to be zero so make sure you select
simple average and here you want to type
a zero for the base temperature
and then we need to use metric units
down here because the way the growing
degree days are calculated it has to be
calculated
with celsius degrees not fahrenheit so
make sure you select metric here and
there's two different options down here
for the output you can either have it
display on the screen which is this html
or you can select um csv which will
download a file if you want to track it
and add to it and and
manipulate the data later i'm just going
to display it on the screen because
we're just interested in seeing uh what
the data is and what it looks like so i
selected the the station we've got our
simple average uh base temperature zero
i've got metric selected um i got the
output i want to just put it on the
screen and do html now we just got to
select the dates and i'm going to choose
here
february 1. just to make sure we get
enough data in here to to really see um
i don't expect back in february we we
had very many um days where the average
temperature was above freezing but um
i'm just going to select these days to
start with so i'm going to hit generate
report
and then it brings up a report it's got
the heading on here tells you which um
station it was the at and and the
information from there and then you get
these columns with you got your date in
the first column you got your air
temperature maximum for the day you got
your air temperature minimum for the day
and then this is your growing degree day
average um so this is your average
temperature for the day
and you can see back on february 1st
2021
it was 8.9 degrees
celsius
was a high temperature negative 6.5 was
a low temperature the average was 1.2 so
we actually accumulated 1.2 uh growing
degree days or heat units for wheat
so in order for green up to occur
we have to have seven days in a row
where this is a positive number now
notice it reports zeros if it's a
negative number so it won't never report
a negative number because it
just because your temperatures are cold
it doesn't go backwards
um so we're looking where we have seven
of these
positive in a row and as you scroll down
i can see a little bit there i got a
couple days where we had some there
another two days or we had some heat
units a little bit warmer out but we
still got some zeros there we had a
little bit um had a couple of days here
and you can see down here we only only
had two days in a row here of positive
heat accumulation on the 14th and 15th
of march
so if the forecast and the forecast does
look like we've got another five days
coming where the average temperature
will be above freezing um if that was
the case then um
the the the
date that greenup would occur would be
five days from from march 15th or it
would be on march 20th so um for the
current year we have not reached green
up yet at um this east lansing location
so let me scroll back up here and let me
go back to last year let's just see what
happened last year so i'm just going to
hit my back button on the screen
and i'm going to go back here and i want
to leave all the stuff the same i want
the simpler average the base zero um i
want the metric and i want it displayed
on the screen but let's just go look at
2021 instead
and see what happened in 2021 and i'm
going to move this a little bit later
to make sure i capture the
uh you know the seven days in a row so
i'm going to take this all the way to
the end of march so we're going back to
2021 at this east lansing location i'm
going to generate the report
here's the report we've got the same
columns now notice this is 2021 here
and so we're looking at this column here
this average and you can see down here
as i scroll down we got zero zero zeros
and then here i've got a positive a
positive but then we got back to zero so
we got positive positive and back to
zeros so we still don't have our green
up we gotta have seven of these in a row
so here's one day two days three days
four days
five days six days this is the seventh
day right here so on this date
um on 3 14
uh was the day that we reached green up
at the east lansing location uh so march
14 2021.
so this is a way to use the the data and
the information
to determine when you reach some of the
different growth stages now one thing
that you can do if you want to start
tracking this or keep track maybe you
want to create a spreadsheet that has
this over time and you could do multiple
years in here just select this csv and
re-run this report and then what it does
is notice it generates a excel file you
click on the excel file open it up and
it basically puts this information
in an excel file instead of having it
display on the screen so you still got
your dates um in here for 2021 you've
got your columns here and down here is
where you had your
seven days in a row
um so on this date here um this is
when you had your your uh
green up actually occurred on this
particular
file so if you have any questions please
contact me uh at uh p e n n
n
msu.edu or 269-832-0497

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