Modify landuse and GREENFRAC

Questions related to the use of new landuse, or geographical static data, or to modifications to the existing data
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siyuzh
Posts: 2
Joined: Fri Aug 21, 2020 5:53 pm

Modify landuse and GREENFRAC

Post by siyuzh » Mon Aug 24, 2020 4:14 pm

Hi,

I am using WRFv4.1, sf_surface_physics=2 (unified Noah Land surface model), and sst_update =1. I would like to change the dominant land use category for a region. I could change LU_INDEX and LANDUSEF in geo_em.d0x.nc, but I do not know how to modify GREENFRAC accordingly.

My questions are:
1. How will GREENFRAC be processed in later modeling processes, in metgrid, real.exe and wrf.exe? What output variables will be influenced?
2. Should I modify other variables in geo_em.d0x.nc: ALBEDO12M, LAI12M, and URB_PARAM etc.?
3. For a certain land use category, are there reference values for GREENFRAC? How should I modify GREENFRAC according to landuse changes?

Thanks for your help!

Siyu

kwerner
Posts: 2287
Joined: Wed Feb 14, 2018 9:21 pm

Re: Modify landuse and GREENFRAC

Post by kwerner » Tue Sep 01, 2020 5:47 pm

Hi Siyu,
I apologize for the delay in response. As GREENFRAC is a 12-monthly field from geogrid, during the real.exe process, it will be interpolated to the model start time, and stored in the array "vegfra." It will also be included in wrflowinp_d* since you are using sst_update. As for modifying other variables, I guess it depends whether you think those particular variables will be affected in the area of your modifications. ALBEDO12M isn't even actually used during real/wrf unless you set usemonalb= .true. in the namelist (it will be interpolated to "albbck" during real). Many of the options given by geogrid static data are not used during wrf - they use the VEGPARM.TBL values instead.
NCAR/MMM

siyuzh
Posts: 2
Joined: Fri Aug 21, 2020 5:53 pm

Re: Modify landuse and GREENFRAC

Post by siyuzh » Tue Sep 01, 2020 5:59 pm

Thanks for your reply!

Is 'vegfra' or 'lai' used in unified Noah Land Surface Model in WRF? Would it influence surface energy fluxes or wind/temperature fields in the WRF output?

Siyu

kwerner
Posts: 2287
Joined: Wed Feb 14, 2018 9:21 pm

Re: Modify landuse and GREENFRAC

Post by kwerner » Fri Sep 04, 2020 7:37 pm

Siyu,
It looks like both vegfra and lai are computing during WRF with the Noah surface scheme. It's likely that they can have an effect on the energy fluxes and other fields.
NCAR/MMM

psagar
Posts: 8
Joined: Mon Jan 14, 2019 7:36 am

Re: Modify landuse and GREENFRAC

Post by psagar » Wed Apr 21, 2021 9:14 am

Answer by 'kwerner' was very helpful. I am using WRF3.8.1 and I see that with 'usemonalb' set true, the albedo (ALBBCK) is used from geo_em* files (variable ALBEDO12M) as said. Now, I want to know the source of data used by ALBEDO12M. Is it AVHRR or MODIS or something else? Could you please clarify?

kwerner
Posts: 2287
Joined: Wed Feb 14, 2018 9:21 pm

Re: Modify landuse and GREENFRAC

Post by kwerner » Thu Apr 22, 2021 9:05 pm

@psagar,
Take a look at this FAQ page. It provides the extent of information we have on the static data.
NCAR/MMM

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