I'm currently working on hydrological modeling by using the soil moisture method in WEAP. I have a problem with the result because my baseflow is always higher compared to the observed flow. So, I took time to work on PEST then I adjusted sensitive parameters such as SWC, RZC, PFD, RRF, DWC, DC, Z1 and Z2, and Kc.
After have adjusted these parameters, result change but not too much.
So to get a good result, I tended to increase the evaporation in order to reduce runoff by increasing the value of Kc (over 1). The result was good after applying some statistical indicators such as R2, NSE, RSR, PBIAS. However, it was not logical since the evaporation was too high.
And one more thing which is a real problem is my baseflow in sim higher than baseflow in observation but peak flow in simulation smaller than in observation.
The question is how can I reduce based flow and increase peak flow?
I don't know how much you increase the Kc because it has a reasonable range. You have to change in these ranges of variation. You can find the range of Kc from literature review or FAO publications.
Before calibration, be sure about the rainfall data, then using other studies on the area for checking the surface water and groundwater interaction. It might be the river has seepage and infiltration to groundwater. This issue depends on topography, geological formation, and the conductance of river bed.
In some basins, interaction is the main cause of river flow variation.