VPDmod Function

public function VPDmod(Ta, RH, kd) result(f)

compute vapor pressure deficit modifier.

References:

Landsberg, J. J., and R. H. Waring, 1997: A generalised model of forest productivity using simplified concepts of radiation-use efficiency, carbon balance and partitioning. For. Ecol. Manage., 95, 209–228.

Dingman, S. L., 2002: Physical Hydrology. Prentice Hall, 646 pp

Arguments

Type IntentOptional Attributes Name
real(kind=float), intent(in) :: Ta
real(kind=float), intent(in) :: RH
real(kind=float), intent(in) :: kd

Return Value real(kind=float)


Variables

Type Visibility Attributes Name Initial
real(kind=float), public :: estar

saturation vapor pressure [mbar]
real(kind=float), public :: vpd

vapor pressure deficit [mbar]

Source Code

FUNCTION  VPDmod &
!
(Ta, RH, kd) &
!
RESULT (f)

IMPLICIT NONE

!Arguments with intent(in):
REAL (KIND = float), INTENT(IN) :: Ta ! current air temperature [°C] 
REAL (KIND = float), INTENT(IN) :: RH ! air relative humidity [0-1] 
REAL (KIND = float), INTENT(IN) :: kd ! Stomatal response to VPD [mbar]  


!local declarations:
REAL (KIND = float) :: f
REAL (KIND = float) :: estar !!saturation vapor pressure [mbar]
REAL (KIND = float) :: vpd !!vapor pressure deficit [mbar]
!---------------------------------------end of declarations--------------------
!compute saturation vapor pressure in the air (Dingman, 2002) [mbar]
estar = 6.1076 * EXP ( (17.269 * Ta) / (Ta + 237.3) )

!compute vapor pressure deficit
vpd = estar * ( 1. - RH )

!compute modifier
f = EXP ( - kd * vpd)

!final boundary check
IF ( f > 1.) THEN
    f = 1.
END IF

IF ( f < 0.) THEN
    f = 0.
END IF

RETURN
END FUNCTION VPDmod