Negative values for precipitation

[Federica Gobattoni]

Hi,

I'm working a series of precipitation values with a great number of anomalies. I corrected the precipitation values accordingly but, afeter the corrections, I have some negative values for precipitation. Maybe I could put these negative values equal to zero but how SWAT would work with some negative values for precipitation? SWAT will consider these negative values as NO DATA and then it will interpolate to have new data for those NO DATA values? Or it will put the negative values to zero? 

Thank you so much,

Federica

[Jim Almendinger]

Federica --

The only negative values for precipitation (P) should be -99, which indicates a missing value to SWAT.  SWAT would then (I believe) revert to estimating precipitation based on its weather generator program.  Unless I'm missing something obvious, I don't see how any other negative values for P would be sensible.  

Assuming that you are in control of the time series of P that you are inputting to SWAT (whether an actual record, or a simulated record that you generated), then I would advise removing all -99 values.  If you have more than one station, then fill in missing P values with those from the next nearest station, or use an average of existing stations.  SWAT does not do this interpolation among existing stations for you (not that I know of).  

Best regards,

-- Jim

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Dr. James E. Almendinger, Senior Scientist
St. Croix Watershed Research Station
Science Museum of Minnesota
16910  152nd St. N
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