Hydrological calibration and vegetation

[Bastian Ringleb]

Dear Tom and all,

I have another question on the hydrological calibration. I work on a catchment in Germany - so temperate climate. I ran the model with several different manning n's and compared model discharge to real discharge (black line). I think the model reflects the winter discharge quite well (plot 1). But when I look at non-winter months the model overestimates the discharge (plot 2).

For me the most logical reason is, that during summer months the vegetation, evapotranspiration retains alot of water and therefor discharge in this catchment stays low.

But how do you reflect that in a model? Would you reduce precipitation amounts during summer month to better reflect the available runoff or should you work with the real precipitation amounts and discuss that model time does not reflect a real timescale?

Best wishes,

Bastian

[tom.co...@gmail.com]

Hi Bastian – the summer discharges (observed – black yes?) look really low – which seems a but unusual..

The main value to alter the hydrology is not mannings n – but the m value in topmodel. I suspect you may need a higher value for this – which will mean it under estimates the peak in mid Jan – but may do better with the others.. I’ll guess m is set at 0.005 at the moment? If so maybe try 0.015 or 0.02?

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[Bastian Ringleb]

Hi Tom,

thanks for the quick answer - yes I changed the m-value to alter the hydrology (and not mannings n - I confused them in my head).

Your right black is the observed discharge of my catchment. The m-value for these calibration runs (Discharge_r10 - r12) was already set at 0.03 as 0.015 and 0.02 was giving me more pronounced peaks. Should this be set any higher?

[tom.co...@gmail.com]

You can try higher – for sure.

Any groundwater effects? Karst/limestone/chalk etc..?

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[Bastian Ringleb]

yes - limestone, karstic features in the upper part of the catchment.