LAI12 and GREENFRAC in geo_em file v.s LAI and VEGFRA in wrfout file

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Chang_Shu
Posts: 29
Joined: Mon Jan 06, 2020 4:28 am

LAI12 and GREENFRAC in geo_em file v.s LAI and VEGFRA in wrfout file

Post by Chang_Shu » Wed Jul 21, 2021 4:52 pm

Hello, WRF team

I am doing research using WRF to analyze the relationship between urban heat islands and the urban vegetation/green area.
I noticed there are two variables, LAI12 and GREENFRAC, in the geo_em file that might be related to the vegetation condition in the study region.
I believe the LAI12 should be the Leaf Area Index for the 12 months, so I am wondering what is the variable GREENFRAC.
I guess it should be the green fraction, but where can I find the defining equation for GREENFRAC?

I also find the two variables LAI and VEGFRA in the wrfout files, but I noticed the distributions of these two variables are different from that of the LAI12 and GREENFRAC in geo_em file. Is it correct? And if they are different from the two variables in the geo_em files, what are the definitions for these two variables (LAI and VEGFRA) then in the wrfout file.

Thank you,

Chang

kwerner
Posts: 2433
Joined: Wed Feb 14, 2018 9:21 pm

Re: LAI12 and GREENFRAC in geo_em file v.s LAI and VEGFRA in wrfout file

Post by kwerner » Mon Jul 26, 2021 10:18 pm

Hi Chang,
You are correct that LAI12 is the Leaf Area Index for 12 months. GREENFRAC is a field interpolated from MODIS FPAR and 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." However, if you're using the Noah LSM scheme, then LAI and VEGRA are computed during WRF, meaning the value for GREENGRAC in geogrid will be overwritten by the new computed value for VEGFRA by the Noah scheme. The Noah scheme uses the VEGPARM.TBL for its values.
NCAR/MMM

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