R/variables_air_humidity_2.R

In BrazilMet: Download and Processing of Automatic Weather Stations (AWS) Data of INMET-Brazil

#' Actual vapour pressure (ea) derived from relative humidity data
#' @param tmin A dataframe with minimum daily air temperature (°C)
#' @param tmax A dataframe with maximum daily air temperature (°C)
#' @param rh_min A dataframe with minimum daily relative air humidity (percentage).
#' @param rh_mean A dataframe with mean daily relative air humidity (percentage).
#' @param rh_max A dataframe with maximum daily relative air humidity (percentage).
#' @examples
#' \dontrun{
#' ea <- ea_rh_calculation(tmin, tmax, rh_min, rh_mean, rh_max)
#' }
#' @export
#' @return Returns a data.frame object with the with ea from relative humidity data.
#' @author Roberto Filgueiras, Luan P. Venancio, Catariny C. Aleman and Fernando F. da Cunha


ea_rh_calculation <- function(tmin, tmax, rh_min, rh_mean, rh_max) {
  if (is.null(tmax) | is.null(rh_min)) {
    ea_rh <- as.data.frame((0.6108 * exp(17.27 * tmin / (tmin + 237.3))) * (rh_max / 100))
  } else {}

  if (is.null(rh_max)) {
    e_tmax <- 0.6108 * exp(17.27 * tmax / (tmax + 237.3)) # e_tmax (kPa)
    e_tmin <- 0.6108 * exp(17.27 * tmin / (tmin + 237.3)) # e_tmin (kPa)
    ea_rh <- as.data.frame((rh_mean / 100) * ((e_tmin + e_tmax) / 2))
  } else {
    e_tmax <- 0.6108 * exp(17.27 * tmax / (tmax + 237.3)) # e_tmax (kPa)
    e_tmin <- 0.6108 * exp(17.27 * tmin / (tmin + 237.3))
    ea_rh <- as.data.frame((e_tmin * (rh_max / 100) + e_tmax * (rh_min / 100)) / 2)
  }
  colnames(ea_rh)[1] <- "ea_rh"
  return(ea_rh)
}

#' Vapour pressure deficit (es - ea)
#' @param tmin A dataframe with minimum daily air temperature (°C).
#' @param tmax A dataframe with maximum daily air temperature (°C).
#' @param tdew A dataframe with dewpoint temperature (°C).
#' @param rh_min A dataframe with minimum daily relative air humidity (percentage).
#' @param rh_mean A dataframe with mean daily relative air humidity (percentage).
#' @param rh_max A dataframe with maximum daily relative air humidity (percentage).
#' @param ea_method The methodology to calculate the actual vapour pressure. Assume the "rh" (default) for relative humidity procedure and "dew" for dewpoint temperature procedure.
#' @examples
#' \dontrun{
#' ea <- es_ea_calculation(tmin, tmax, tdew, rh_min, rh_mean, rh_max, ea_method)
#' }
#' @export
#' @return Returns a data.frame object with the ea from relative humidity data.
#' @author Roberto Filgueiras, Luan P. Venancio, Catariny C. Aleman and Fernando F. da Cunha


es_ea_calculation <- function(tmin, tmax, tdew, rh_min, rh_mean, rh_max, ea_method) {
  if (is.null(ea_method)) {
    ea_method <- "rh"
  }
  # - Mean saturation vapor pressure derived from air temperature

  e_tmax <- 0.6108 * exp(17.27 * tmax / (tmax + 237.3)) # e_tmax (kPa)
  e_tmin <- 0.6108 * exp(17.27 * tmin / (tmin + 237.3)) # e_tmin (kPa)
  es <- (e_tmax + e_tmin) / 2
  es <- as.data.frame(es)

  if (ea_method == "dew") {
    # - Actual vapour pressure (ea) derived from dewpoint temperature

    ea <- as.data.frame(0.6108 * exp(17.27 * tdew / (tdew + 237.3)))
  } else {
    # - Actual vapor pressure (ea) derived from relative humidity data

    if (is.null(tmax) | is.null(rh_min)) {
      ea <- (0.6108 * exp(17.27 * tmin / (tmin + 237.3))) * (rh_max / 100)
    } else {

    }
    if (is.null(rh_max)) {
      e_tmax <- 0.6108 * exp(17.27 * tmax / (tmax + 237.3)) # e_tmax (kPa)
      e_tmin <- 0.6108 * exp(17.27 * tmin / (tmin + 237.3)) # e_tmin (kPa)
      ea <- as.data.frame((rh_mean / 100) * ((e_tmin + e_tmax) / 2))
    } else {
      e_tmax <- 0.6108 * exp(17.27 * tmax / (tmax + 237.3)) # e_tmax (kPa)
      e_tmin <- 0.6108 * exp(17.27 * tmin / (tmin + 237.3))
      ea <- as.data.frame((e_tmin * (rh_max / 100) + e_tmax * (rh_min / 100)) / 2)
    }
  }
  es_ea <- as.data.frame(es - ea)
  colnames(es_ea) <- "es_ea"
  return(es_ea)
}

#' Relative humidity (rh) calculation
#' @description Relative humidity is calculated in this function based on minimum air temperature of the day and the air temperature of the moment.
#' @param tmin A dataframe with minimum daily air temperature (°C)
#' @param tmean A dataframe with mean air temperature (°C) that you want to calculate the relative humidity.
#' @examples
#' \dontrun{
#' rh <- rh_calculation(tmin, tmean)
#' }
#' @export
#' @return A data.frame object with the relative humidity calculated
#' @author Roberto Filgueiras, Luan P. Venancio, Catariny C. Aleman and Fernando F. da Cunha


rh_calculation <- function(tmin, tmean) {
  e_tmin <- 0.6108 * exp(17.27 * tmin / (tmin + 237.3))
  e_t <- 0.6108 * exp(17.27 * tmean / (tmean + 237.3))
  rh <- 100 * (e_tmin / e_t)
  rh <- as.data.frame(rh)
  colnames(rh) <- "rh"
  return(rh)
}