PRMS Solar Radiation Module

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Detailed Description

Presents the USGS Precipitation Runoff Modeling System (PRMS) Solar Radiation simulation module.


Date Taken:

Length: 00:05:16

Location Taken: Lakewood, CO, US


Steve Markstrom: Hello, we’re continuing
the PRMS training video series.

I’m talking about the solar radiation distribution
process and the modules that you can use.

Basically there are three.

You can see them down there, ddsolrad, ccsolrad,
climate_hru and basically you can specify

which one of these three you want to use in
the control file.

The job of these modules, or what needs to
be done by this process is we need solar radiation

at all the HRUs.

And we’ve either got it at a point or we
have the tables, the solar tables that came

from the solar table process and we need to
come up with the daily solar radiation on

the HRUs.

And that’s what this is about.

So in the case of the ddsolrad or degree-day
module, basically, you can see the equation

down here.

This variable here, swrad, that’s the solar
radiation on the HRU, on any HRU, on any given


You can see these two graphs here.

Basically, what you do, is you enter this
left hand graph with the daily temperature

on the HRU, maximum temperature.

You come up and you see these two parameters,
dday_slope and dday_intercept, they define

this line.

So where that temperature comes up and intersects
the line, you come across to this curve over

here on the right hand part of the graph.

Then you intersect that and you come down.

And what that does is it gives you this value
of, in the code it’s called solf.

And basically what it is, the ratio of actual
to potential solar radiation.

And then that value is used in this equation.

So here, you’ve got the soltab_potsw, that’s
the value that comes from the solar table.

You’ve got this parameter here hru_slope.

So you’ve got all of the values you need,
then you compute the daily short wave solar

radiation on the HRU.

We can look at the other module.

The ccsolrad or cloud cover solar radiation

You can see the equations here.

Basically, tmax and tmin, those are computed
for each HRU.

You’ve got these two parameters.

Cloud_cover plugs into this equation.

Crad_coef that’s another parameter.

So from those equations you’re able to compute
the solf value.

And then it’s the same equation again.

Swrad is equal to the same equation.

Different ways of computing this ratio of
potential to actual solar radiation.

One thing we do, I included this, is we get
these maps of solar radiation.

This are expected actual solar radiation,
from NREL, the National Renewable Energy Laboratory.

So if you’re putting solar panels on your
house, or something, this would be the information

that they provide to you, but we use it to
calibrate our model.

In this case you can see how solar radiation
is varying spatially and by month.

These are good calibration data sets.

One final thing on this solar radiation distribution

There is always a questions about units.

So our modules are outputting solar radiation
in Langlys.

Which is one calorie per centimeter squared.

And for those of you who have forgot your
high school chemistry, a calorie, the definition

of a calorie that we are going to use here
is it raises one cubic centimeter or gram

of water one degree C. Right, so very convenient
units to go from energy directly to temperature.

Then, if you are thinking about a more modern
or common set of units, Watts per meter squared,

you can see, the conversion factor between
one Langley per day to Watts per meter squared.

That concludes the solar radiation distribution