PRMS Overview

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Detailed Description

Presents overview of the USGS Precipitation Runoff Modeling System (PRMS) software as part of a training series.


Date Taken:

Length: 00:09:30

Location Taken: Lakewood, CO, US


Steve Markstrom: Hello.

This is Steve Markstrom.

I work with the US Geological Survey in Lakewood,

This is part of the PRMS training video series.

Going to give a quick overview of the Precipitation
Runoff Modeling System, or PRMS.

This is our latest version.

Here's the schematic showing how PRMS views
the hydrologic cycle.

Basically, these components are simulated
on...every HRU, hydrologic response unit,

in a watershed.

Basically up here are the inputs, to the model,
air temperature, precipitation, soil radiation,

if you have it.

Things are computed down through the plant

Here's the soil surface, the root zone, soil
zone down through the depth of the roots.

Then deeper than that is the fully-saturated
zone, these arrows right here represent the

components that are summed together that contribute
to stream flow.

This diagram comes directly from our users'
manual, which brings up a good point, documentation.

We get a lot of questions about PRMS documentation.

The first thing we offer is a PRMS users'

This is pretty new.

It came out this year.

You can go this URL right here, get it, or
you can go to the USGS publications warehouse.

Just type that into Google, and you can search
for my name or PRMS, whatever, you'll get

this techniques and methods document.

The second resource is the PRMS web page.

There's a lot of stuff here, including the
current executable and the source code and

previous versions of PRMS going back, I don't
know, several years.

You can get all that stuff there.

There's the URL for that.

That's where you're going to have to go to
get the model.

The third resource we offer are the training
videos of which this one that you're viewing

is part of.

You can get these from our website and just
click through them.

Basically, these are pattern off of the training
course, our standard PRMS training course,


These are the lectures that we present during
the week-long training course.

Reports and articles also, if you go to our
website, there's a page there that has basically

everything that's been published about PRMS
that we know of, there could be more.

This is a pretty good resource, a lot of USGS
report series and journal publications as


There's the URL for that.

Finally, as we release new versions of PRMS,
we update a few of the tables.

In appendix one, there's a table that lists
the modules, a table that listed dimensions,

a table for parameters, and a table for variables.

If there are any changes, basically these
would corresponded changes to input and output

of the model.

If there are changes for the current version,
you can click on this link right here and

get these revised tables.

Here's an example of an updated version of
table 1-5.

It's been updated for PRMS version 4.0.1.

Basically, anything that's different from
the published table and the users' manual

is highlighted.

You can see we added a few variables.

If you look at these things, these are just
summary variables that don't really change

anything that the models do.

The users need to know that they're there.

If you are running PRMS, you should download
these tables for a version that you just downloaded.

Those are on the PRMS page as well.

Basically, PRMS uses the continuity equation
at it's heart.

The change and storage is equal to input minus
output minus error.

You can see some of the terms in this equation
that we're looking at, very general overview

of how PRMS works.

PRMS does have a relatively standard set of
units or dimensional analysis of the units,


Any kind of storage in the model is expressed
in depth per unit area.

What that means is that volume is expressed
in terms of length.

Likewise, flux is expressed in terms of depth
per unit area per time step.

Since the time step is always one day, that
tends to go away, that part of's

just dividing by one here.

Basically, our storage and our flux are in
unit that we can go back and forth with.

PRMS scale.

We have successfully applied PRMS on watersheds
of tens to tens of thousands of square kilometers

with our HRUs can be much less than a square

If you watch this video series all the way
through, you'll see some scales that are much

larger than tens of thousands of square kilometers.

Temporal scale, one to hundreds of years are
pretty typical on a daily time step.

Discritization of space.

To set up PRMS, you need to have essentially
maps of definitely these first three and optionally,

sub-basins, if you're going to use sub-basins
in your model.

PRMS needs to know exactly what is in and
what is out of your modeling application.

Stream segments need to be defined, as well
as space needs to be discretized into what

we're calling "Hydrologic response units."

Just a few terms that we use and have a very
specific meaning for PRMS, process and modules.

Within PRMS, a process represents one of the
major hydrological process or an administrative


PRMS has 17 processes.

If you look at table two in the users' manual,
you can see the processes listed right here.

We have many presentations in the series,
PRMS training series go into these processes

in much more detail.

A module is a piece of source code used by
PRMS to simulate a process.

PRMS has 39 modules.

And obviously, because we have more modules
and processes, the user has the option, in

some cases, to choose which module they want
to use for simulation of a specific process.

In this case, we'll back to table two.

In here, on the left hand column, you can
see a list of modules.

Modules listed.

For here, precipitation distribution process.

You can see we have four modules.

Any one of those could be used to simulate
that process.

Dimensions, a dimension is a value.

It's an integer value that's used to describe
the number values of a parameter or variable,

getting parameters and variables next.

Every parameter variable has at least one

A dimension is comprised of a name and an
integer value.

Dimensions are read from the PRMS parameter

I'll describe the parameter file later.

Here's table 1-1.

It is listing the dimensions and little description,
default values, and some notes about them.

Anyway, here's where you can go and see the

PRMS also has a concept of parameters.

Basically, a parameter is a static input value
that does not change during a course of the


Parameters are declared by the active modules.

Basically, the modules that are actually being
used for simulation of the different processes.

Parameters are declared as arrays.

Even if there's only one value for that parameter,
then it's an array size of one.

Values for the parameters are read from the
input parameter file.

It could be real or integers.

Here's table 1-3.

This table is a pretty big table, lists all
of the parameters that are in the current

version of PRMS.

You can see the parameter and names, some
descriptions, which dimension is associated

with the parameter, the type, units, valid
range of the parameters, the default value

and then some notes over here about use of
the parameter.

PRMS also has a concept of variables.

A variable is a value that can change each
time during the simulation.

Likewise, they are declared by the active
modules in PRMS as well, must be declared

as arrays just like the parameters.

The input variables, not all variables are
input but the input variables are read from

the data file and are real or integers.

Table 1-5 lists all of the input and output
variables, another big table in the appendix

of the PRMS users' guide.

You can see the variable names, descriptions,
again, dimensions, units, the type and some

note about using that particular variable.

That concludes this quick overview of PRMS.

Thanks for watching.