# Question about modifying the lookup table for the LCZ, i.e., URBPARM_LCZ.TBL

#### xyp

##### New member
Dear all,

I am trying to modify the vegetation fraction for certain categories of the LCZ. I did this by modifying the ‘FRC_URB’ in the URBPARM_LCZ.TBL, which refers the fraction of the urban landscape without natural vegetation. So logicaly, the vegetation fraction should be equal to 1 - FRC_URB. The model ran successfully, however, the output VEGFRA remained the same after modifying FRC_URB, while the meteorogical variables changed.

Therefore my questions are:
1. Is it correct to change vegetation fraction by modifying FRC_URB in the URBPARM_LCZ.TBL? If not, how to do it?

2. What is the physical meaning of the modifying FRC_URB? If it is reduced to 0, what becomes of the original building fraction?

3. Is there any guideline or link to learn how URBPARM_LCZ.TBL works when runing WRF-LCZ?

Kind regards.

Dear all,

I am trying to modify the vegetation fraction for certain categories of the LCZ. I did this by modifying the ‘FRC_URB’ in the URBPARM_LCZ.TBL, which refers the fraction of the urban landscape without natural vegetation. So logicaly, the vegetation fraction should be equal to 1 - FRC_URB. The model ran successfully, however, the output VEGFRA remained the same after modifying FRC_URB, while the meteorogical variables changed.

Therefore my questions are:
1. Is it correct to change vegetation fraction by modifying FRC_URB in the URBPARM_LCZ.TBL? If not, how to do it?
VEGFRA is derived from GREENFRAC in REAL program. GREENFRAC is from static input data in GEOGRID. I don't think you can change VEGFRA by changing FRC_URB.

2. What is the physical meaning of the modifying FRC_URB? If it is reduced to 0, what becomes of the original building fraction?
It is urban fraction of each grid cell. Its value is read into WRF from various URBPARM.TBL.
3. Is there any guideline or link to learn how URBPARM_LCZ.TBL works when runing WRF-LCZ?

Kind regards.
Do you mean how the values in URBPARM_LCZ.TBL are specified? If you just want to know how this table is used, please look at the code phys/module_sf_urban.F.

xyp

According to your reply, the change to FRC_URB cannot modify the vegetation fraction in the LCZ grid cell. May I know What changes should I make to modify the vegetation fraction in the LCZ grid? Should it be by modifying the VEGFRA in the static input data, like Wrfinput_d04.nc, geo_em.d04.nc, or met_em.d04?

Thanks again,
Kind regards.

VEGFRA is derived from GreenFRAC from WPS static data. A simple way to change its value is to modify its value in wrfinput.

xyp
Thank you very much for your answer; it means a lot to us!

We have two questions regarding the modifications to the VEGFRA variable in wrfinput and would appreciate your expert insights.

1. Given that VEGFRA has different values within the same LCZ, should we ensure that VEGFRA + FRCURB ≤ 1 when making modifications?
2. When VEGFRA + FRCURB < 1 in a specific grid cell, what is the physical significance of the remaining fractions of the grid cell? Does it indicate bare land or an impervious surface?
Kind regards

I am not sure of these questions. I will send your post to our expwert and hope he can get back to you soon.

Thank you for your help. I look forward to hearing good news.