CN parameter range

[kima...@gmail.com]

Dear all,

Im new to SWATCUP and would appreciate some advice. It might be a very elementary question. 

I have used SWATCUP to calibrate my model. However, using NSE as the objective function- I get a good result (NS= 0.53) when the program uses a CN value of -0.700159. 

I am not sure this can be correct, or can it be? When I read up about the range of CN it needs to be 35-98. But in other answers on this group it is suggested to lower the CN to negative values if the runoff is very high (which my catchment does result in). 

My other parameters for that iteration are all in the suggested range, it is only the CN that worries me.

Thanks for any advice,

Kim

[Karim Abbaspour]

what are the calibrated CN values?

 

--
You received this message because you are subscribed to the Google Groups "SWAT-CUP" group.
To unsubscribe from this group and stop receiving emails from it, send an email to swat-cup+u...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

[kima...@gmail.com]

The value given under the calibration outputs, best_par.txt, for CN is -0.700159. With a min value: -0.725681 and max: -0.215233.

[afshin]

If i understand your question correctly, it can be explained with CHANGE MOOD of parameter. can find in parameterization section in the manual of swat cup.

[Abbaspour, Karim]

This is a relative change factor, i mean actual values in the .mgt files. 

[kima...@gmail.com]

So if the type of change applied to CN is "relative", then for this example, if the parameter value is suggested at -0.700159, the program would multiply the CN actual value by ( 1+ (-0.700159) ). 

My actual/original CN value in the SWAT model for the initial SWAT simulation is 65. So the SWATcup program will change it to: 65 * (( 1+ (-0.700159) ). If I calculate this myself I get a suggested best parameter value of 19.489 for CN from SWATcup. Does this seem correct?

Thanks so much for the help. I appreciate it.

[Karim]

No, CN2 should not be that small. You should carefully set initial values on CN2 using landuse and soil, and then adjust it slightly, say plus minus 0.2. Now, CN2 is perhaps compensating for other parameters that are not in their proper ranges.

[kima...@gmail.com]

Ok thank you. I think that would make sense- I thought the initial run with the SWAT gave relatively good results, so during calibration- I adjusted minimally, only adjusting : CN2, GW_DELAY, ALPHA_BF and GWQMN. My catchment has alot of runoff (it is mountainous, very little soil),so I just assumed CN2 would be very important. But SWAT seems to be overpredicting peak flows, and underpredicting base flow. So suggestions seem to be to adjust the following parameters aswell as the first four: GW_REVAP, REVPMN, SOL_AWC, ESCO.