[If we assume your model is verified and all correct, no bug, no human error]

SCS curve number is not a physical model, it is lumping couple of effects in a one single number (Curve Number) as it is heavily calibrated, it yields good results most of the times. However, consider SCS method is dumping a lots of non-linear effects in one single value and it does not always give you correct results. I am not against that method, I only say you have to use it with open eyes.

Back to your question: as your rainfall length is relatively high, your soil is saturated and CN is not correct anymore, you cannot change CN value in one simulation so to get correct results you better use a more physical based model: For example use Richards Equation, or Horton formula for infiltration and Kinematic Wave for runoff. Then you would see saturation of the soils and you would not have that problem.

Hope this helps you.

Kaveh

Dear Dr Stephen

The logic in physics indicates that the sum of the entries equals the sum of the outputs.

In the case of precipitation, there are several factors of the decrease in the volume of water entering (precipitation) because of permeability, evaporation. That is to say: that rainfall is much less than runoff

For this purpose, I advise you to revise this method SCS CN

Best reagrds

Dear Stephen,

In greeting you, I would like to ask.

How are the soil moisture conditions?

If the soil is already saturated and there are areas of impermeability, it is possible.

But only in a moment, a day, a month. Not the whole series

Dear Serrao,

i agree with you. I have only certain values that are greater than precipitation. I want to validate my runoff values using my observed streamflow values. Could you tell me how?

Dear Stephen,

We usually use statistical performance indicators, such as: Nash-Sutcliffe, Willmott's concordance index, Determination Coefficient and Pearson's correlation among others ...

Please note the following paper in section 2.2 Calibration, validation, and statistical analysis: http://dx.doi.org/10.1590/s1982-21702019000300018

http://www.scielo.br/pdf/bcg/v25n3/1982-2170-bcg-25-03-e2019018.pdf

Hope this helps,

Sincerely

Thank you sir. Could you tell me how to do it excel?

In excel, all you have to do is sum the entire data series (observed and estimated) and average them both. And then use the equations.

Basically it is: Sum of estimated minus sum of observed, divided by sum of observed minus average of observed etc ...