Spatial distribution of rain gauges

[ChristianKjaer]

Dear SWAT users

According to the SWAT input/output file documentation, SWAT does not
use the information on latitude and longitude provided (about the rain
gauges) in the .pcp file.

How does SWAT obtain this geographical information - if at all?

And if SWAT does not obtain it, does it mean I will have to do the
averaging (of rain gauges within each subbasin) myself and then
provide exactly 1 rain gauge in the .pcp file per subbasin?

If the latter is the case, how does SWAT now which rain gauge belongs
to which subbasin? Is it just the first one belonging to subbasin 1,
the next to subbasin 2 and so on..? At last, if this is really true, I
am surprised that the averaging functionality is not inside SWAT, and
I don't understand why this matter is not described in the input/
output documentation.

I hope some of you can help me out here :)

Thanks in advance.
Christian Kjaer Jensen
Stud. Environmental Enginnering at the Technical University of Denmark

[Rosemary Records]

Hi Christian:

SWAT assigns one of your rain gauges to each subbasin...whether or not it is in the subbasin I think it is the gauge that's closest to the subbasin centroid, so your coordinates should actually be used by SWAT (I'm not sure what the documentation was referring to about coordinates of gauges not being used).  Actually, if you dig through the Access database of your SWAT project I believe you can even find which gauge is assigned to which basin...I don't have a SWAT project handy to check right now, but I think there is a table in the Access database ("pcp" or something similar) with this information documented.

You will not have to do averaging yourself...SWAT will not average anything, just assign the data from the closest rain gauge and fill in the "-99" missing days with data from the weather generator.

Does that help?

Rosie Records

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Rosemary Records
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Colorado State University
California Cooperative Fish & Wildlife Research Unit
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[ChristianKjaer]

Dear Rosemary (and other SWAT users)

I recieved a few replies - thank you for your that. I appreciate it!
Just to clear things up completely I would like to specify my problem
a little more.

SWAT is getting the rain data from a pcp1.pcp file. In the
doumentation (ftp://ftp.brc.tamus.edu/pub/swat/doc/swat2005/SWAT
%202005%20io.pdf) on page 135 and onward it is stated that the spatial
information (lat/lon) about each gauge in the pcp1.pcp file is not
used by SWAT.

As far as I understand ArcSWAT is using a different kind of input
table which also has spatial information about each gauge. See the
documentation (http://www.geology.wmich.edu/sultan/5350/Labs/
ArcSWAT_Documentation.pdf) on page 22-23. If you have the
documentation on SWAT 2009 it is page 23-24. As far as I understand
ArcSWAT is selecting one gauge inside every subbasin (or averaging
e.g. with Thiessen polygons) and then creating one resulting rain
gauge for each subbasin. The resulting rain gauges is then placed in
the pcp1.pcp file for SWAT to read.

Now, I don't know how SWAT will know which rain gauges (in the
pcp1.pcp file) belongs to which subbasin. One way could be that they
are simply placed in the file according to the number of the given
subbasin. But this is not clear from the documentation (see the first
link of this message).

It is important for me to know because I'm working on a project that
is dedicated to using open-source software. So instead of ArcSWAT and
ArcGIS I am using MWSWAT and MapWindow. And afterwards I am
manipulating the input text files for SWAT manually.

I realize that the whole matter is a bit cryptical. Thank you for
taking your time!

All the best
Christian

On Apr 13, 7:07 pm, Rosemary Records <rosem...@lamar.colostate.edu>
wrote:

> Rosem...@lamar.colostate.edu<Rosemary.Reco...@humboldt.edu>
> Rosemary.Reco...@humboldt.edu

[Chris]

Hi Christian,

You are right that ArcSWAT (or MWSWAT) uses the geographic location to assign rain gauge data to subbasins.  The assignment is recorded in the .sub file for the subbasin, in variable IRGAGE.  A value of 0 means no measured precipitation, 1 means use the first precipitation column in pcp1.pcp, etc.

Chris

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[Jim Almendinger]

I'm jumping into the middle of things here, so perhaps I've missed something.  But Rosie's explanation seems exactly right to me.  ArcSwat uses one input file for rain gauge locations (generally in projected coordinates), and then it uses individual files with the time-series data for each gauge.  It then constructs the precipitation files (text files in textinout folder) that are read by the SWAT executable.  Each subbasin gets the precipitation values from the gauge that is nearest to its centroid.  There is no averaging going on that I know of.  Perhaps these rules are different for sub-daily precipitation data (which I haven't used) -- but I doubt it.  To summarize -- ArcSwat makes the connection between the rain gauges and subbasins, and then writes the files needed by SWAT.  SWAT doesn't need to know the locations of the gauges because by the time SWAT reads the input, each subbasin has already been assigned to a rain gauge (simply the nearest one -- and thus not generally within the subbasin itself).  

Really, the simplest thing here is to run one or more of the example models that download with ArcSwat.  You'll find the input files (both the location file and data files).  Run the model and then look at the data in the txtinout folder to see how ArcSwat constructed the files needed by Swat.  I believe MWSwat also downloads with examples.  

Finally, if you're interested in more detailed precipitation manipulation, then look into the auxiliary program PCP_SWAT written by Xuesong Zhang and Srini.  This program will take precipitation data from any number of stations, create a surface of precip values for each day of your simulation by the method of your choice (typically by kriging), and output daily values for each of your subbasins.  I.e., it creates a pseudo-station for each subbasin and populates its daily precip values based on smoothing (spatially averaging) the available data.  This really is more along the lines of what you have been assuming that ArcSwat / Swat does.  

Cheers,

-- Jim

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[Justin Goldstein]

I agree fully with Jim and Rosie on everything, especially with regard
to PCP_SWAT. Well stated! My calibration statistics jumped
significantly when utilizing that tool precisely because I'm working
in an area with heavy, extremely localized precipitation. The
improvement in calibration statistics is also consistent with the
literature. Just be sure that you have a 32-bit system if you'd like
to use it.

-Justin

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[Ercan]

Hi Christian Kjaer Jensen  and Chris,

The explanation bellow is legitimate to me. I knew SWAT uses same precipitation depth over a subbasin which support the statement bellow. What did you (Christian Kjaer Jensen ) end up with this problem? 

Thanks,

Mehmet.

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[Mehmet]

I verified that SWAT uses IRGAGE (.sub) to determine which column in pcp file to use. When there are more than one pcp file, IRGAGE should be determined based on NRTOT and NRGFIL (.cio) (e.g. when pcp1.pcp and pcp2.pcp has 5 stations in each, column 1 in pcp2.pcp should be considered as column 6 or IRGAGE = 6). 

Mehmet.

[DP]

Hi I guess, I am responding to such detailed discussion of precipitation after a long time. I agree that the spatial distribution of precipitation in SWAT is not robust unless some one has enough gauge station within the basin to adequately represent the spatial distribution of localized rainfall. However, with regard to this PCP_SWAT does gives a closer approximation of spatial rainfall distribution of rainfall over the basin by kriging or by some other interpolation method.
So,  I was wondering why in ArcSWAT this option was not included as an alternative after its development in 2010?

It would be much more beneficial for for improving model prediction.

Cheers.

[Adriana Calderon]

Hello, is the PCP _SWAT an extension? or it is a different program

Can you send me the link of where I can get it_?

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[Jim Almendinger]

PCP_SWAT is an extension to ArcMap (not within ArcSWAT), if I remember correctly.  It is several years old and I don't know if it's available for the newer versions of ArcMap or not, and nor do I know where you might find a download (unless it is on the SWAT website somewhere). 

The simplest thing would be to re-delineate your watershed into a finer mesh of subbasins, which is often desirable anyway because it increases the spatial resolution of your model.  But of course, the more subbasins (and HRUs) you have, the slower your model will run.  I commonly have several hundred subbasins and several thousand HRUs, but many projects discussed here in the forum are much larger. 

-- Jim

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[Xuesong Zhang]

To follow up Jim and Adriana's communications which mentioned pcp_SWAT, I would like to share a link with the community at http://xzhang.pbworks.com/w/page/27189956/FrontPage. 

The pbworks site hosts the data, tutorial, paper, and extension program for pcp_SWAT. Note that the arcGIS9.X version is what we originally developed and described in the JAWRA paper. Later Dr. Zhonglong Zhang transferred the code to arcGIS10.0. 

For now I do not have time to further upgrade the code for more advanced versions of ArcGIS. Hope the existing materials at the website will help future use of pcp_SWAT to ensure quality of precipitation data for SWAT modeling, particularly in regions with sparse rain gauges.

Cheers,

Xuesong Zhang

On Thu, Oct 19, 2017 at 6:41 AM, Jim Almendinger <jalmen...@smm.org> wrote:

PCP_SWAT is an extension to ArcMap (not within ArcSWAT), if I remember correctly.  It is several years old and I don't know if it's available for the newer versions of ArcMap or not, and nor do I know where you might find a download (unless it is on the SWAT website somewhere). 

The simplest thing would be to re-delineate your watershed into a finer mesh of subbasins, which is often desirable anyway because it increases the spatial resolution of your model.  But of course, the more subbasins (and HRUs) you have, the slower your model will run.  I commonly have several hundred subbasins and several thousand HRUs, but many projects discussed here in the forum are much larger. 

-- Jim

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[anasale...@gmail.com]

Dear Xuesong, I would like to know if it was possible to update the code from PCP_SWAT to ARCGIS version 10.1.

Cheers,

Ana Luisa

Em sexta-feira, 20 de outubro de 2017 19:52:00 UTC-2, xuesong escreveu:

To follow up Jim and Adriana's communications which mentioned pcp_SWAT, I would like to share a link with the community at http://xzhang.pbworks.com/w/page/27189956/FrontPage. 

The pbworks site hosts the data, tutorial, paper, and extension program for pcp_SWAT. Note that the arcGIS9.X version is what we originally developed and described in the JAWRA paper. Later Dr. Zhonglong Zhang transferred the code to arcGIS10.0. 

For now I do not have time to further upgrade the code for more advanced versions of ArcGIS. Hope the existing materials at the website will help future use of pcp_SWAT to ensure quality of precipitation data for SWAT modeling, particularly in regions with sparse rain gauges.

Cheers,

Xuesong Zhang

On Thu, Oct 19, 2017 at 6:41 AM, Jim Almendinger <jalmen...@smm.org> wrote:

PCP_SWAT is an extension to ArcMap (not within ArcSWAT), if I remember correctly.  It is several years old and I don't know if it's available for the newer versions of ArcMap or not, and nor do I know where you might find a download (unless it is on the SWAT website somewhere). 

The simplest thing would be to re-delineate your watershed into a finer mesh of subbasins, which is often desirable anyway because it increases the spatial resolution of your model.  But of course, the more subbasins (and HRUs) you have, the slower your model will run.  I commonly have several hundred subbasins and several thousand HRUs, but many projects discussed here in the forum are much larger. 

-- Jim

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[Lidiia Iavorivska]

Dear SWAT Group and Dr. Zhang,

 

I am trying to use PCP_SWAT (updated version PCPSWAT_08_22_2010.dll for ArcGIS 10.0) to generate interpolated time series of precipitation for SWAT.

However, I can’t get it to work: it seems to have trouble with establishing the connection between the plug-in, the ArcMap .mxd project, and the workspace folder directory.

 

Following the steps outlined in the manual, I created and saved a “test.mxd” project, then installed the PCP_SWAT plug-in within that project, and lastly saved the project. All the data folders, the “test.mxd” project, and the installation .dll file were placed within the same folder, similar to what is shown in the manual. After clicking on the plug-in icon, I get the following error message: “Please select .mxd file, and the document should be saved first”. It still opened the SWAT_PCP interface window, but the fields for Interpolation workspace and the locations of output files and folders are greyed out and not pre-populated with the destination paths, unlike what is shown in the example screenshots.

 

Interestingly, I got the program to work the very first time I installed the plug-in; it ran the data and produced outputs. After that, I tried to recreate the same steps (including re-installing the ArcMap and the plug-in) on the same and other 32 bit computers, and it did not work.

 

Can anyone who used the software before please advise the right sequence of steps or point out what I am doing wrong? Any suggestions will be greatly appreciated.

 

Thank you,

Lidiia Iavorivska

On Friday, October 20, 2017 at 5:52:00 PM UTC-4, xuesong wrote:

To follow up Jim and Adriana's communications which mentioned pcp_SWAT, I would like to share a link with the community at http://xzhang.pbworks.com/w/page/27189956/FrontPage. 

The pbworks site hosts the data, tutorial, paper, and extension program for pcp_SWAT. Note that the arcGIS9.X version is what we originally developed and described in the JAWRA paper. Later Dr. Zhonglong Zhang transferred the code to arcGIS10.0. 

For now I do not have time to further upgrade the code for more advanced versions of ArcGIS. Hope the existing materials at the website will help future use of pcp_SWAT to ensure quality of precipitation data for SWAT modeling, particularly in regions with sparse rain gauges.

Cheers,

Xuesong Zhang

On Thu, Oct 19, 2017 at 6:41 AM, Jim Almendinger <jalmen...@smm.org> wrote:

PCP_SWAT is an extension to ArcMap (not within ArcSWAT), if I remember correctly.  It is several years old and I don't know if it's available for the newer versions of ArcMap or not, and nor do I know where you might find a download (unless it is on the SWAT website somewhere). 

The simplest thing would be to re-delineate your watershed into a finer mesh of subbasins, which is often desirable anyway because it increases the spatial resolution of your model.  But of course, the more subbasins (and HRUs) you have, the slower your model will run.  I commonly have several hundred subbasins and several thousand HRUs, but many projects discussed here in the forum are much larger. 

-- Jim

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[KAUEM SIMOES]

HI Dip

So in my case my project has 9 rainfall stations outside my basin, Indaia basin, Minas Gerais, Brazil. I do not have rainfall stations inside the basin. Ten sub-basins were delineated for this basin.

If I put the 9 stations I have in the pcp.txt file and run the swat, it generates a PC1.PCP with only 2 stations.How does he make this choice? What is the criterion? Is it by the centroid method?

Is it worth using the Thiessen method and generating 10 virtual stations in these 10 sub-basins? Will I have better results?

Will a PC1.PCP file with 10 stations be created? Should I use other methods like kriging?

Thank you for your support.

[Natalja C.]

Hello,

These are all good questions to ask.

The stations for the pcp file are chosen by distance. If only 2 out of 10 were chosen - then that means that only these two stations are the closest to your subbasins.

All of the other answers really depend on your study region. You should consult a weather/climate specialist of your region, who could tell you if these particular stations could be used to represent what is happening in your watershed. If not - then that person could also suggest on the best statistical method to create your own representative data series.

Best,

Natalja

[Shobhit Pipil]

I am working on Swat project and the catchment area is 406 sq.km. but I feed 1 km*1km gridded precipitation data. Pcp1.pcp only takes gauge station lat-long value precision to single digit and therefore there is an overlap between different gauge station.

Please help me to resolve this problem.

Thanks

[Natalja C.]

Hello,

Are your sub0basins also 1km x 1km or smaller? If not - then it is not possible to do what you want.

pcp station to subbasin is a 1 to 1 relationship. Basically, if you have a subbasin which is , say 6 km2 (2x3), then only ONE station is set to this subbasin, and not 6.

If your subbasins are indeed smaller than 1sq.km. then I would suggest editing the pcp and the stations in the sub files manually. SWAT (not ArcSWAT) doesn't care where your stations are, it operates on command. ArcSWAT is the one, who "prescribes" these commands. You cannot change how ArcSWAT handles pcp files, so you have the only option is to do it in another way, avoiding arcswat.

Best,

Natalja