PRMS Transpiration Period Module

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Detailed Description

Presents the USGS Precipitation Runoff Modeling System (PRMS) Transpiration Period simulation module.


Date Taken:

Length: 00:05:32

Location Taken: Lakewood, CO, US


Jacob LaFontaine: OK, so this presentation
focuses on the transpiration period process

of PRMS.

So there are three primary methods or options
currently in PRMS to look at when transpiration

in occurring throughout the time and across
the basin.

The first is transp_frost.

Which is a killing frost method, which looks
at the point in the fall and the point in

the spring at which your air temperatures
cross a certain threshold or you get no more

temperatures below a certain threshold.

Transp_tindex is a temperature index method
that looks at when you pick a month to where

you say transpiration starts, then there is
a certain number of degrees per day that get

summed up to reach that threshold at which
you say transpiration starts.

And thirdly, you can also use the climate_hru
capability and use an externally preprocessed

values through time and by HRU.

So looking at the killing frost method, PRMS
will generate these parameters that you need

to run this option based off of your temperatures.

And so the two pieces of the control file
parameters that you would want to change are

the model_mode, normally says DAILY and you
want to change that to FROST.

And then the transp_module you would make
that transp_frost on that fourth line.

And so the parameters that are generated when
you run the model in this form of the model_mode

is FROST, it creates a frost_date.param file
and those can be added to your existing parameter

file to use this method and that generates
fall_frost, spring_frost, frost temperature

and two basin parameters which if we look
in the table 1-3 of the manual, you see three

of those parameters.

Where the fall_frost is the solar date from
the first killing frost of the fall.

And the frost temperature is your threshold
where you say it’s a killing frost.

And the spring is at which you start transpiring

And so there are some default values at which
those are set to.

As far as the temperature which is 28 degrees

And that’s all adjustable for that threshold
and the others are based off of what you’ve

set for that and running the FROST mode.

Now, transp_frost when you want to run the
model to generate your hydrologic response,

you change the model_mode back to DAILY and
still keep the transpiration module the same.

And it still uses those same parameters and
then you would get your hydrologic response

that way.

Now the other method of transpiration, transp_tindex.

So this looks at, once you decide that a certain
month is when you’re going to start looking

for transpiration, it adds up daily values
of temperature.

And so that one the model_mode is DAILY and
transp_module is transp_tindex.

And the three parameters that PRMS uses there
are the beginning month, the ending month

and the number of degrees that you are summing

So back in table 1-3, has descriptions of
those three parameters, so the beginning month

can be set anywhere from 1 to 12 which is
January to December.

Transp_end can be set anywhere from 1 to 13,
if you choose 13 then that means that you’re

treating every month as that it could possibly
have transpiration.

Which maybe something that you may see in
warmer climates, but maybe not in the colder

areas that you may run the model.

And the tmax, transp_tmax is the number of
degrees that you are actually summing up.

And so a range that we have here is from 0
to 1000, default is 1.

The typical value maybe like 500 that folks
typically use for that value.

Then the third is climate_hru.

So this would be some externally processed
method of determining if transpiration is

occurring on an HRU.

And so in addition to having the transpiration
method set to climate_hru, you would also

include the file of these preprocessed values.

And so you’d have this transp_day and you
would have the path to your externally created

file and the variable that’s included in
that file is transp_on.

And so that’s a binary one or zero by day
and by HRU to say whether or not transpiration

can occur or not.

And here’s just the typical example of a
CBH or climate by HRU file.

And so the top line you designate the dimension
nhru with the number of HRUs in your model.

The four pound signs separates it from the
time series.

And then you have your date stamp portion
and then your values.

Here I have seven example HRUs where three
of them transpiration is on and four are turned

off, with the ones and the zeroes.

That concludes this portions of the PRMS training
course and you can refer to the manual or

our help form for any questions you may have.