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The official repository for the Weather Research and Forecasting (WRF) model
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Potential bug for initializing urban fraction #2039

Open cenlinhe opened 2 months ago

cenlinhe commented 2 months ago

Currently, in the real.exe step (module_initialize_real.F), if a grid is urban type but FRC_URB2D in that grid is zero (e.g., outside US over urban regions; FRC_URB comes from NLCD in WPS and thus no data outside US), then the real.exe will assign 0.9 for the FRC_URB2D as a default initial value. (see code here: https://github.com/wrf-model/WRF/blob/develop/dyn_em/module_initialize_real.F#L3159-L3163).

However, this real.exe treatment prevents the urban model from reading in the FRC_URB values from URBPARM.TBL during the urban parameter initialization module for grids without FRC_URB data (now set to 0.9 by real.exe). See code here: https://github.com/wrf-model/WRF/blob/develop/phys/module_sf_urban.F#L2810-L2818. In this case, the table value will not be effective since it is already replaced by the default 0.9 value from real.exe.

Potential solution/bug fix: (1) commenting out the setting of 0.9 in module_initialize_real.F; or (2) add a if-statement to limit this 0.9 default setting to only places where NUDAPT (or NLCD) data is available.

cenlinhe commented 2 months ago

@barlage @tslin2 Could you please take a look when you have time?

barlage commented 2 months ago

@cenlinhe I guess the main question I have is: what do we want the code to be doing? Is there something beyond a quick fix that we should do? There are so many switches now for data sources, the logic is getting a little messy and confusing. I'm not sure what the motivation is for the default setting of 0.9, but that seems over prescriptive to me.

cenlinhe commented 2 months ago

@barlage I agree. At some point, we need to clean up things for urban part. I also agree that the default setting of 0.9 is unnecessary and probably we should remove it.

cenlinhe commented 2 months ago

Here is a history commit for this part of code added to WRF: https://github.com/wrf-model/WRF/commit/748beef81b95d159c6147420eeb802f6a739beb3

tslin2 commented 2 months ago

0.9 is used as it is the default assumption in the model that high density residential urban type is used if urban type is not given, which is the same as the default table. However, if someone wants to change the table values and does not provide a spatial map, that would be the problem.

tslin2 commented 2 months ago

Another related issue is the landcover. The landcover is different if comparing the no urban model (option 0) to the urban model (1, 2, or 3). https://github.com/wrf-model/WRF/blob/b7f31dcde42beb4be468edb0541ec02f23b20455/dyn_em/module_initialize_real.F#L3153

cenlinhe commented 2 weeks ago

@Yuqi-Ng @chenghaow Could you please take a look?