# difference between LAI and GREEN FRACTION

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#### fatememohsni

##### New member
Dear All,
I am working with geographical static data and trying to find out their influence on an emission dust storm. Hence I have some questions:

1) The amounts of LAI and vegfra in WRF output and Green Fraction in WPS output are different, although I set sst_update=1 , rdlai2d = true and auxinput4_inname = 'wrflowinp_d<domain>' . When I checked output by ncview, while the range of Green Fraction is between 0 and 0.78, Vegrfa is between 0 and 53. Why do we have this significant difference?

2) As far as I learn, there is 2 option for vegetation in the model. LAI and fPAR which the latest shows by green fraction in wps and vegfra in wrf, is it right? Why does the model use 2 options? is the model interpolating them or using both of them directly?

3) I have changed both variables (LAI and GREEN FRCATION) in wps and wrf and I noticed that although the amount of dust load did not change dramatically with the change in leaf area index, this changed dramatically with GREEN FRACTION. It is puzzled me what is the difference between them. cIs it possible that in the emission equations we don't use LAI ?

4) After running WPS for 2 different months and observing output by ncview, I realized that The amount of LAI and GREEN FRCTION for all the months is equal. Does it mean that for every month we have just a number?

Kind regards,

Hi,
1) The amounts of LAI and vegfra in WRF output and Green Fraction in WPS output are different, although I set sst_update=1 , rdlai2d = true and auxinput4_inname = 'wrflowinp_d<domain>' . When I checked output by ncview, while the range of Green Fraction is between 0 and 0.78, Vegrfa is between 0 and 53. Why do we have this significant difference?

LAI and green fraction are not physiccally same. Although they sound similar, their definition and quantification are different.

2) As far as I learn, there is 2 option for vegetation in the model. LAI and fPAR which the latest shows by green fraction in wps and vegfra in wrf, is it right? Why does the model use 2 options? is the model interpolating them or using both of them directly?

This is because in the land module, both variables are used.

3) I have changed both variables (LAI and GREEN FRCATION) in wps and wrf and I noticed that although the amount of dust load did not change dramatically with the change in leaf area index, this changed dramatically with GREEN FRACTION. It is puzzled me what is the difference between them. cIs it possible that in the emission equations we don't use LAI ?

Dear Ming,

1) My point is the amount of GREENFRAC in WPS is between 0 and 0.78 and the amount of VEGFRA is between 0 and 58. It means probably the model read vegetation parameter from the table instead of wps output. Although I set :
sst_update=1 , rdlai2d = true , and auxinput4_inname = 'wrflowinp_d<domain>' , io_form_auxinput4 = 2
How can use wps green fraction in wrf?

2) I am wondering to know more about how are used of LAI and green fraction variables in the model. Is there any source I can use it?

Hi,
1) My point is the amount of GREENFRAC in WPS is between 0 and 0.78 and the amount of VEGFRA is between 0 and 58. It means probably the model read vegetation parameter from the table instead of wps output. Although I set :
sst_update=1 , rdlai2d = true , and auxinput4_inname = 'wrflowinp_d<domain>' , io_form_auxinput4 = 2
How can use wps green fraction in wrf?

VEGFRA is percentage vegetation fraction. This variable is later devised by 100 to obtain similar value range to GREENFRAC
In REAL program, greenfrac is processed and output as vegfra, which is the variable later used in WRF.

2) I am wondering to know more about how are used of LAI and green fraction variables in the model. Is there any source I can use it?

Various LSM modules use LAI and green fraction (vegfra). Let's take Noah as an example, you can find the related information in phys/module_sf_noahdrv.F.

A R