Is total evaporation is the sum of its sub-components?

UW-Hydro / VIC

The Variable Infiltration Capacity (VIC) Macroscale Hydrologic Model

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Is total evaporation is the sum of its sub-components? #158

Closed jhamman closed 10 years ago

jhamman commented 10 years ago

Fixing #147 has raised the concern that the sub-components of total evaporation may not all be updated properly after evaporation is rescaled (as it is in runoff.c). It would be good to confirm that it is updated and that:

OUT_EVAP = OUT_EVAP_BARE + OUT_EVAP_CANOP + OUT_TRANSP_VEG + OUT_SUB_SNOW + OUT_SUB_CANOP

bartnijssen commented 10 years ago

"it would be good" - as in "this will be done" or as in "crossing our fingers and hope for the best"? I'd much prefer the "this will be done" version...

On Nov 18, 2014, at 12:15 PM, Joe Hamman notifications@github.com wrote:

Fixing #147 has raised the concern that the sub-components of total evaporation may not all be updated properly after evaporation is rescaled (as it is in runoff.c). It would be good to confirm that it is updated and that:

OUT_EVAP = OUT_EVAP_BARE + OUT_EVAP_CANOP + OUT_TRANSP_VEG + OUT_SUB_SURFACE + OUT_SUB_CANOP

— Reply to this email directly or view it on GitHub.

jhamman commented 10 years ago

Ok, I did some looking into this and it does not look like there is a problem here. My understanding of how this works is:

The fraction of evaporation and transpiration (bare_evap_frac) is held constant after being calculated in func_surf_energy_bal.c.
The total amount of ET is scaled as necessary to close the water balance in runoff.c
Finally, the output variables OUT_EVAP_BARE and OUT_TRANSP_VEG use bare_evap_frac to partition the flux in put_data.c

The two plots below illustrate my findings a bit more.

Plot 1 show the total EVAP compared to the individual components and the ERROR calculated as:

df['EVAP_ERROR'] = df['EVAP'] - (df['EVAP_BARE'] + df['EVAP_CANOP'] + df['TRANSP_VEG'] + df['SUB_SNOW'] + df['SUB_CANOP'])

wb_et_ok Plot 2 zooms in on the calculated error showing that it merely round off errors in the ASCII output:
wb_et_ok2

jhamman commented 10 years ago

@tbohn , if you feel good about my assessment, go ahead and close the issue...

tbohn commented 10 years ago

Thanks Joe. I don't have permission to close the issue, but I'm OK with closing it.

On Tue, Nov 18, 2014 at 4:12 PM, Joe Hamman notifications@github.com wrote:

@tbohn https://github.com/tbohn , if you feel good about my assessment, go ahead and close the issue...

— Reply to this email directly or view it on GitHub https://github.com/UW-Hydro/VIC/issues/158#issuecomment-63570419.