Steve Markstrom: Hello.
This is Steve Markstrom.
I work with the US Geological Survey in Lakewood, Colorado.
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 canopy.
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' manual.
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,
week-long.
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
well.
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,
basically.
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 the...it'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 kilometer.
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
task.
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 dimension.
A dimension is comprised of a name and an integer value.
Dimensions are read from the PRMS parameter file.
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 dimensions.
PRMS also has a concept of parameters.
Basically, a parameter is a static input value that does not change during a course of the
simulation.
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.