Question About Runoff Calculation Using SFCRUNOFF and UGDRNOFF in WRF-Hydro v5.3

[nuts sun]

Hi everyone,

I am currently using WRF-Hydro version 5.3 and would like to calculate the spatial distribution of runoff from the model outputs. However, I have some questions regarding the runoff-related variables and would greatly appreciate your guidance.

For reference, I have enabled channel routing with the following settings in my namelist:

text

! Switch to activate channel routing...(0=no, 1=yes) CHANRTSWCRT = 1 !<-- Turn on/off channel routing module. ! Specify channel routing option: ! 1=Muskingum-reach, 2=Muskingum-Cunge-reach, 3=Diffusive Wave-gridded channel_option = 2 !<-- If channel routing module is active, select which physics option to use.

My current understanding is that total runoff at a grid cell may be represented as the sum of surface runoff and subsurface runoff. To estimate these components, I am using:

• SFCRUNOFF from the RESTART output files as surface runoff.
• UGDRNOFF from the LDASOUT output files as subsurface (underground) runoff.

I would like to confirm the following:

1. Is it correct to interpret SFCRUNOFF as the grid-cell surface runoff component and UGDRNOFF as the grid-cell subsurface runoff component?
2. Are these two variables defined in a way that allows them to be combined directly at the grid-cell level?

3. Can total runoff be calculated as:

   Runoff = SFCRUNOFF + UGDRNOFF

   for each grid cell?

4. Are there any differences in temporal meaning (e.g., instantaneous values, accumulated values, or time-step averages) between these two variables that should be considered before combining them?
5. If this approach is not recommended, what would be the preferred method for deriving the spatial distribution of total runoff from WRF-Hydro outputs?

My objective is to obtain a physically consistent runoff field for water budget analysis and spatial runoff assessment.

Thank you very much for your time and assistance. I would greatly appreciate any clarification you can provide.

Best regards,

NMV