SWAT+ precipitation not matching observed pcp file (generator being used?)
Vrashesh Karkar
Hi everyone,
I’m running into a precipitation issue in SWAT+ that I haven’t been able to resolve and was hoping someone here might have seen this before.
I’m using one observed precipitation station (Albion CA) with a full daily pcp file (2013–2025). The file format is correct (YEAR, Julian day, value), no missing days, no -99 values. In the Editor, simulated precipitation is unchecked, precipitation lapse rate is 0, and elevation bands are off.
Even with this setup, SWAT+ is not using the observed values. For example, on 2016-01-06 my input pcp file clearly has 0.0 mm, but the model outputs about 11.4 mm, and this value is identical across all HRUs and at the basin level. This isn’t a one-day issue it happens on multiple dates.
I do have Wengen defined as a weather generator station (since SWAT+ won’t run without one), but Albion CA is the only station with observed precipitation linked. The distance between Albion CA and Wengen is about 13 km.
Since all HRUs show the same value, it looks like the model is pulling precipitation from a single source, possibly the generator, even though the observed pcp file is correctly linked.
A few things I’m trying to understand:
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Can the wgn station override observed precipitation under some conditions?
-
Is there any distance or assignment logic where SWAT+ falls back to the generator even when an observed pcp is available?
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Is there a way to check, per HRU or per day, which precipitation source/file was actually used?
Any suggestions on what to check next would be really appreciated. I can share the relevant input files if that helps.
Due to large file size (>25mb) I sharing link to access the txtinout.zip file
Thanks in advance,
Vrashesh
Nancy B. Sammons
Vrashesh:
The name of the measured file contains a space/blank, so the model isn’t finding data from a file named ‘Albion’. I suggest an underscore instead of a blank space.
Rename the measured file to the same changed name and also in the ‘pcp.cli’ file.
pcp.cli: Precipitation file names - file written by SWAT+ editor 2026-01-03 19:34:05.058587
filename
Albion_CA.pcp
Let me know if you have any questions or further issues.
Nancy
From: swatplu...@googlegroups.com <swatplu...@googlegroups.com>
On Behalf Of Vrashesh Karkar
Sent: Saturday, January 3, 2026 11:08 PM
To: SWAT+ Editor <swatplu...@googlegroups.com>
Subject: [SWAT+ Editor User Group] SWAT+ precipitation not matching observed pcp file (generator being used?)
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Maarten Waterloo
Hi Nancy,
That solved it…
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