meteorological_calculations.F90

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module meteorological_calculations
!! Algorithms to estimate dewpoint, vapor pressure, and other values
!! given input air temperature or solar radiation values.
 
  use iso_c_binding, only : c_int, c_float, c_double, c_bool
  use constants_and_conversions
  implicit none
 
contains
 
elemental function sat_vapor_pressure__e_0(rT) result (re_0)
    !! Calculate saturation vapor pressure
    !! @note Implemented as equation 11 in:
    !!    Allen, R.G., and others, 1998, FAO Irrigation and Drainage Paper No. 56,
    !!    Crop Evapotranspiration (Guidelines for computing crop water
    !!    requirements), Food and Agriculture Organization, Rome, Italy.
 
  real (c_float), intent(in)   :: rt
      !! Air temperature in °C
  real (c_float)               :: re_0
      !! Saturation vapor pressure at given air temperature, in kilopascals
 
  re_0 = 0.6108_c_double * exp(17.27_c_double * rt      &
                                / ( rt + 237.3_c_double)  )
 
end function sat_vapor_pressure__e_0
 
!--------------------------------------------------------------------------
 
elemental function dewpoint_vapor_pressure__e_a(fTMin) result (fe_a)
    !! Estimate dewpoint vapor pressure given a minimum daily air temperature value
 
  real (c_float), intent(in) :: ftmin
      !! Minimum daily air temperature, in °C
  real (c_double) :: fe_a
      !! Dewpoint vapor pressure at given air temperature, in kiloPascals
 
  fe_a = 0.6108_c_double * exp( 17.27_c_double * f_to_c(ftmin) &
             / ( f_to_c(ftmin) + 237.3_c_double) )
 
end function dewpoint_vapor_pressure__e_a
 
!--------------------------------------------------------------------------
 
elemental function equivalent_evaporation(rR) result(rR_ET)
    !! Calculate a radiation value in terms of equivalent evaporation (depth of water
    !! that would be evaporated for a given radiation value)
 
  real (c_double), intent(in) :: rr
      !! Input radiation, in \‍(\frac{MJ}{m^2 \cdot day}\‍)
  real (c_double) :: rr_et
      !! Radiation expressed as equivalent evaporation, in \‍(\frac{mm}{day}\‍)
 
  rr_et = rr * 0.408_c_double
 
end function equivalent_evaporation
 
 
 
end module meteorological_calculations