SNFRAC.f

      SUBROUTINE snfrac (SNEQV,IVEGx,SNCOVR)

!- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
       implicit none
       include 'mpif.h'
      
! ----------------------------------------------------------------------
! 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) :: ivegx
      REAL,intent(in) ::  sneqv
      REAL,intent(out) ::  sncovr
      REAL salp,snup(20),rsnow
      integer iveg

      DATA salp /4.0/
      DATA snup /0.080, 0.080, 0.080, 0.080, 0.080, 0.020,        &
     &            0.020, 0.060, 0.040, 0.020, 0.010, 0.020,       &
     &            0.020, 0.020, 0.013, 0.013, 0.010, 0.020,       &
     &            0.020, 0.020/
     
! ----------------------------------------------------------------------
! SNUP IS VEG-CLASS DEPENDENT SNOWDEPTH THRESHHOLD ABOVE WHICH SNOCVR=1.
! ----------------------------------------------------------------------
!jjt
        iveg = ivegx
        IF ( iveg > 20 .or. iveg < 1 ) then
!          print *, ' PROBLEM in SNFRAC, IVEG = ',iveg
           iveg = 1
        END IF
        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