values in basin_wb_aa is not the average of basin_wb_yr

[Joana Eichenberger]

Hi everyone, 

I ran my model for the period 1990–2020, using 1990–1992 as the warm‑up years. I’ve noticed that the values reported in basin_wb_aa don’t match the average of the corresponding values in basin_wb_yr. For example, basin_wb_aa reports 848.84 mm of precipitation, but when I calculate the average annual precipitation from basin_wb_yr for 1993–2020, I get 851.99 mm. Has anyone encountered this discrepancy or knows what might explain the difference?  

Best regards,

Joana

[henryc]

hi Joana!

If I remember correctly from my past experience, it depends on how the warm-up period is treated in the outputs. In the case of basin_wb_yr, the period 1990–1992 is simply not printed, whereas in basin_wb_aa the statistics are calculated over the entire period (1990–2020). You could test this by reducing the warm-up period to 0 years and comparing the results. I’m not sure whether this should be considered a bug or whether it is still present in the latest version of the model.
Hope this helps.

enrico

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[Joana Eichenberger]

Hi Enrico. When I run the simulation without warm-up period from 1990-2020 I get 853.6 mm in basin_wb_aa and an average of 854.2 mm in  basin_wb_yr. Athough there is a small difference, this discrepancy could be explained with rounding issues. However, when I ran the simulation with the warm-up period (1990-1992) I got 848.8 mm in basin_wb_aa and therefore it does not seam to calculate the statistics over the entire period...

[henryc]

Hi Joana,

The lower value in basin_wb_aa could mean that the sum over the printable period is divided by the number of years including the warm-up time, I guess. Unfortunately (or not), I cannot find confirmation of this in the current code. Which version of SWAT are you using?

enrico 

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