PRMS Interception Module

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Detailed Description

Presents the USGS Precipitation Runoff Modeling System (PRMS) Precipitation Interception simulation modules.


Date Taken:

Length: 00:03:07

Location Taken: Lakewood, CO, US


Steve Markstrom: Hello this is Steve Markstrom
continuing with the PRMS training series.

This time I’m talking about the interception
module and process.

There’s only one module for this process.

And I only have one slide in my presentation,
so this is going to go pretty quick.

So, what we’re trying to do or what the
module is trying to do is compute this term

net precipitation.

Basically, how much precipitation makes it
through the canopy and hits the ground.

If you look at my little figure here, you
can see there are two aspects of net precipitation.

There’s area where there is no vegetation
canopy and the precipitation falls straight


And then there’s also this through fall
where precipitation is falling on the vegetation,

the canopy becomes full, can’t hold any
more, and then it falls through.

And in this case, those two things summed
together are the net precipitation.

And that’s described by this top equation

You can see the parameters that you as a user
have to input in the parameter file to get

this module to work.

It’s this covden, basically a value, a parameter
for winter and a parameter for summer.

Winter covden and summer covden.

Then depending on your species type down here,
your vegetation, you’ll have some kind of

max storage.

How much can the leaves hold?

And that varies by season as well.

There are a few if statements in here.

Basically, if the leaves are full or if the
leaves aren’t full yet, you get a little

different behavior.

And then, losses, once you get some interception
on the leaves or in the leaves, in the canopy,

then you lose that storage by evaporation.

So, if its rain or liquid water up in the
leaves, it evaporates at the free water surface

evaporation rate or reference rate or PET
rate, whatever you want to call it.

And then if it’s snow, there’s a scheme
where snow sublimates at some percentage of

the reference rate, potential rate.

So there you go, that’s the basic description.

If you have more questions, you can read about
it in the manual too.

That concludes the discussion of interception,
precipitation interception.