LAI_eff Subroutine

public subroutine LAI_eff(mp, lai_pft, HGT_pft, HgtAboveSnow, reducedLAIdue2snow)

This subroutine computes the leaf-area index of a canopy when there is snow present. The formulae assume that the leaf area is distributed uniformly in the vertical within the canopy.

Leaf area, LAI, accounting for the presence of snow, is given by

$$LAI_{snow} = LAI_{nosnow} \frac{h_{c,snow}}{\max(0.01, h_{c,nosnow})}$$

where $h_{c,snow}$ is evaluated in subroutine HgtAboveSnow. The LAI is decreased proportionally to the canopy height with/without snow.

The effective canopy height used to evaluate the proportional decrease in LAI takes a minimum value of 0.01m. This condition prevents numerical issues when the canopy height (without snow) is small.

Warning: To follow up

Can HgtAboveSnow be greater than MAX(0.01, Hgt_PFT)? If yes then there is an issue to resolve. HgtAboveSnow can sit at its minimum value of 10 $z_{0,min}$ so if $10 z_{0,min} > 0.01 > h_{c,nosnow}$ then LAI can increase if there is snow!

Arguments

Type	Intent	Optional	Attributes		Name
integer,	intent(in)			::	mp	Number of land points (-)
real,	intent(in)			::	lai_pft(mp)	Leaf area index without snow (m$^2$ m$^{-2})$
real,	intent(in)			::	HGT_pft(mp)	! height of canopy without snow (m)
real,	intent(in)			::	HgtAboveSnow(mp)	height of canopy above the snow surface (m)
real,	intent(out)			::	reducedLAIdue2snow(mp)	Output. Modified leaf area index for snow (m$^2$ m$^{-2}$)