VP: Actual vapor pressure

Description

Calculate actual vapour pressure [kPa] either from psychrometric data or from relative humidity data.

Usage

VP(
  Tmax = NULL,
  Tmin = NULL,
  Rhmax = NULL,
  Rhmin = NULL,
  interval = "day",
  Tmean = NULL,
  Rhmean = NULL,
  Twet = NULL,
  Tdry = NULL,
  apsy = NULL,
  P = NULL
)

Arguments

Tmax

maximum temperature during 24-hour period (for daily values)

Tmin

minimum temperature during 24-hour period (for daily values)

Rhmax

maximum relative humidity [precent] (for daily values)

Rhmin

minimum relative humidity [precent] (for daily values)

interval

hour, day, week or month

Tmean

Mean air temperature [degreeC] (for periods shorter 1 day)

Rhmean

Mean air humidity [percent] (for periods shorter 1 day or if Rhmax and Rhmin are missing)

Twet

wet bulb temperature (for calculation with psychrometric data)

Tdry

dry bulb tamperature (for calculation with psychrometric data)

apsy

coefficient depending on the type of ventilation of the wet bulb [kPa/(degreeC)] (for calculation with psychrometric data)

atmospheric pressure [kPa]

Details

References

Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. (1998). Crop evapotranspiration-Guidelines for computing crop water requirements-FAO Irrigation and drainage paper 56. FAO, Rome, 300(9).

Examples

Run this code

# NOT RUN {
VP(Tmax = 25, Tmin = 18, Rhmax = 82, Rhmin = 54)
VP(Tmax = 25, Tmin = 18, Rhmean = 68)
# }