WRF impervious area fraction

[jesusff]

There have been some discussions on the difference between the urban and the impervious area fractions (see FPS-URB-RCC/CORDEX-CORE-WG#21).

@LluisFB recently mentioned that 95% impervious fraction is assumed for all LCZs (FPS-URB-RCC/STAGE-0_Analysis#2). Can we confirm this in the code?

[LluisFB]

I already confirmed it from the code, see it from the readme of the urban module in the same GIT
#urbanModule https://github.com/CORDEX-WRF-community/fps-urb-rcc/tree/main/urbanModule

[jesusff]

Sorry, I only see the 0.95 associated to frozen soils. In theory, each LCZ has an assumed impervious fraction, which is much smaller than that:
https://ibis.geog.ubc.ca/urbanflux/resources/lcz.pdf (should be 1-pervious, as there are impervious ground and buildings separately in this resource).

[LluisFB]

@jesusff good to know that this information exists, but as far I checked in the URBPARM_LCZ.TBL, the impervious value is not an entry. It appears, but only used for urb_scheme = 1

# Evaporation scheme for impervious surfaces (for roof, wall, and road)
#            [1: Hypothesized evaporation during large rainfall events (Original)
#            [2: Water-holding scheme over impervious surface, Yang et al., 2014
#      (sf_urban_physics=1)

IMP_SCHEME: 1

# Porosity of pavement materials on impervious surface
# For calculating latent heat flux over impervious surface
# From left to right in order: roof, wall, road
#      (sf_urban_physics=1,IMP_SCHEME=2)
#

PORIMP: 0.45 0.45 0.45 

# Maximum water-holding depth of pavement materials on impervious surface [m]
# For calculating latent heat flux over impervious surface
# From left to right in order: roof, wall, road
#      (sf_urban_physics=1,IMP_SCHEME=2) 
#

DENGIMP: 0.001 0.0002 0.001

So, I dug into the code and I only could found something related as function of the frozen soils (FCR) which is 0.95 to all LCZs