Can you calculate the coefficient of correlation using excel. Calculate NSE, R2, RMSE.

You can use the coefficients I used in this paper.

https://journals.utm.my/mjce/article/view/16216

To calibrate and validate in SWAT, based on the discharge simulations, the monthly or daily model statistics were deemed acceptable if PBIAS < 15%, R2 > 0.6, RSR 0.5. Checking your summary stats file they are within acceptable ranges. You can adjust the parameters to improve you results but it's up to you though.

Check the following references below for more information

** My publication

-Ashu, A.B.; Lee, S.-I. Assessing Climate Change Effects on Water Balance in a Monsoon Watershed. Water 2020, 12, 2564. https://doi.org/10.3390/w12092564

** My references

-Abbaspour, K.C.; Yang, J.; Maximov, I.; Siber, R.; Bogner, K.; Mieleitner, J.; Zobrist, J.; Srinivasan, R. Modelling hydrology and water quality in the pre-alpine/alpine Thur watershed using SWAT. J. Hydrol. 2007, 333, 413–430.

-Schuol, J.; Abbaspour, K.C.; Sarinivasan, R.; Yang, H. Estimation of freshwater availability in theWest African sub-continent using the SWAT hydrologic model. J. Hydrol. 2008, 352, 30–49.

-Nash, J.E.; Sutclie, J.V. River flow forecasting through conceptual model.Part 1-A discussion of principles.J. Hydrol. 1970, 10, 282–290.

-Moriasi, D.N.; Arnold, J.G.; Van Liew, M.W.; Bingner, R.L.; Harmel, R.D.; Veith, T.L. Model evaluation guidelines for systematic quantification of accuracy in watershed simulations. Trans. Am. Soc. Agric. Bio Eng. 2007, 50, 885–900.

- Parajuli, P.B. Assessing sensitivity of hydrologic responses to climate change from forested watershed in Mississippi. Hydrol. Process. 2010, 24, 3785–3797.

Best of luck