WATER BALANCE IN SWAT+

[BB]

Dear all

Is the water balance in SWAT+ correct?

I have run SWAT+ with the LSU (Landscape Unit) option. I have gone through calibration and achieved reasonable performance.

In the Textinout folder, I filtered the basin_wb_aa.csv file, and checked  the annual water balance of the  basin.

I have tried to sum up SURQ, LATQ, ET, and PERC (percolation) and compare it with precipitation (PCP).

As a result

PCP < SURQ+ LATQ+ ET + PERC

The precipitation is always less than the sum of the water balance terms?

Why?

On the precipitation side, however, if I add the SURQ_RUNON and LATQ_RUNON, the result is fine (balanced).

SURQ_RUNON+LATQ_RUNON+PCP = SURQ+ LATQ+ ET + PERC

What does it mean? What is the logic behind this?

What are the meanings of SURQ_RUNON and LATQ_RUNON? in the table?

Great thanks

[Hemant Servia]

I think you are mainly missing the 'change in storage' component in addition to some other components as well while computing the water balance. I would obtain the water balance as under:

where P = Precipitation

delta S =  change in soil water content

delta stor = change in aquifer water content

ET = evapotranspiration (excluding revaporation)

Q = total surface flow = Lateral Flow + surface runoff + return flow

DAr = Deep Aquifer Recharge

ETr = revaporation

Just to mention that there might be a residual error sometimes and that error in my case has mostly been in the range of 3-5 mm when computed at an annual scale. 

I hope it helps.

Hemant Servia

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