SNFRAC_GFS.f

      SUBROUTINE snfrac_gfs(SNEQV,IVEG,SNCOVR)
!
!- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
       implicit none
!      
! ----------------------------------------------------------------------
! SUBROUTINE SNFRAC
! ----------------------------------------------------------------------
! CALCULATE SNOW FRACTION (0 -> 1)
! SNEQV   SNOW WATER EQUIVALENT (M)
! IVEG    VEGETATION TYPE
! SNCOVR  FRACTIONAL SNOW COVER
! SNUP    THRESHOLD SNEQV DEPTH ABOVE WHICH SNCOVR=1
! SALP    TUNING PARAMETER
! ----------------------------------------------------------------------
      integer,intent(in) ::  iveg
      REAL,intent(in) ::  sneqv
      REAL,intent(out) ::  sncovr
      REAL salp,snup(13),rsnow
      integer ii,jj

      DATA salp /2.6/
      DATA snup /0.080, 0.080, 0.080, 0.080, 0.080, 0.080,      &
     &       0.040, 0.040, 0.040, 0.040, 0.025, 0.040,      &
     &       0.025/
     
! ----------------------------------------------------------------------
! SNUP IS VEG-CLASS DEPENDENT SNOWDEPTH THRESHHOLD ABOVE WHICH SNOCVR=1.
! ----------------------------------------------------------------------
        IF (sneqv < snup(iveg)) THEN
          rsnow = sneqv/snup(iveg)
          sncovr = 1. - (exp(-salp*rsnow) - rsnow*exp(-salp))
        ELSE
          sncovr = 1.0
        ENDIF
        sncovr = max(0.,min(sncovr,1.))

      RETURN
      END