R/heat_index.R
In geanders/weathermetrics: Functions to Convert Between Weather Metrics
#' Calculate heat index.
#'
#' \code{heat.index} creates a numeric vector of heat index values from
#' numeric vectors of air temperature and either relative humidity or
#' dew point temperature.
#'
#' @param t Numeric vector of air temperatures.
#' @param dp Numeric vector of dew point temperatures.
#' @param rh Numeric vector of relative humidity (in \%).
#' @param temperature.metric Character string indicating the temperature
#' metric of air temperature and dew point temperature. Possible values
#' are 'fahrenheit' or 'celsius'.
#' @param output.metric Character string indicating the metric into which
#' heat index should be calculated. Possible values are 'fahrenheit' or
#' 'celsius'.
#' @param round Integer indicating the number of decimal places to
#' round converted value.
#'
#' @details Include air temperature (\code{t}) and either dew point
#' temperature (\code{dp}) or relative humdity (\code{rh}). You cannot
#' specify both dew point temperature and relative humidity-- this will
#' return an error. Heat index is calculated as \code{NA} when impossible
#' values of dew point temperature or humidity are input (e.g., humidity
#' above 100\% or below 0\%, dew point temperature above air temperature).
#'
#' @return A numeric vector of heat index values in the metric specified
#' by \code{output.metric}. (If \code{output.metric} is not specified,
#' heat index will be returned in the same metric in which air
#' temperature was input, specified by \code{temperature.metric}.)
#'
#' @note Equations are from the source code for the US National Weather
#' Service's
#' \href{http://www.wpc.ncep.noaa.gov/html/heatindex.shtml}{online heat index calculator}.
#'
#' @author
#' Brooke Anderson \email{brooke.anderson@@colostate.edu},
#' Roger Peng \email{rdpeng@@gmail.com}
#'
#' @references
#' Anderson GB, Bell ML, Peng RD. 2013. Methods to calculate the heat index
#' as an exposure metric in environmental health research.
#' Environmental Health Perspectives 121(10):1111-1119.
#'
#' National Weather Service Hydrometeorological Prediction
#' Center Web Team. Heat Index Calculator. 30 Jan 2015.
#' \url{http://www.wpc.ncep.noaa.gov/html/heatindex.shtml}.
#' Accessed 18 Dec 2015.
#'
#' Rothfusz L. 1990. The heat index (or, more than you ever wanted to know
#' about heat index) (Technical Attachment SR 90-23). Fort Worth:
#' Scientific Services Division, National Weather Service.
#'
#' R. Steadman, 1979. The assessment of sultriness. Part I: A
#' temperature-humidity index based on human physiology and clothing
#' science. Journal of Applied Meteorology, 18(7):861--873.
#'
#' @examples # Calculate heat index from temperature (in Fahrenheit)
#'# and relative humidity.
#'
#' data(suffolk)
#'suffolk$heat.index <- heat.index(t = suffolk$TemperatureF,
#' rh = suffolk$Relative.Humidity)
#'suffolk
#'
#'# Calculate heat index (in Celsius) from temperature (in
#'# Celsius) and dew point temperature (in Celsius).
#'
#'data(lyon)
#'lyon$heat.index <- heat.index(t = lyon$TemperatureC,
#' dp = lyon$DewpointC,
#' temperature.metric = 'celsius',
#' output.metric = 'celsius')
#'lyon
#'
#' @export
heat.index <-
function (t = NA, dp = c(), rh = c(), temperature.metric = "fahrenheit",
output.metric = NULL, round = 0)
{
if(length(output.metric) == 0){
output.metric <- temperature.metric
}
if (length(dp) == 0 && length(rh) == 0) {
stop("You must give values for either dew point temperature ('dp') or relative humidity ('rh').")
}
else if (length(dp) > 0 && length(rh) > 0) {
stop("You can give values for either dew point temperature ('dp') or relative humidity ('rh'), but you cannot specify both to this function.")
}
if (length(dp) != length(t) && length(rh) != length(t)) {
stop("The vectors for temperature ('t') and moisture (either relative humidity, 'rh', or dew point temperature, 'dp') must be the same length.")
}
if (length(dp) > length(rh)) {
rh <- dewpoint.to.humidity(t = t, dp = dp, temperature.metric = temperature.metric)
}
else if (any(!is.na(rh) & (rh > 100 | rh < 0))) {
rh[!is.na(rh) & (rh > 100 | rh < 0)] <- NA
warning("There were observations with an impossible values for relative humidity (below 0% or above 100%). For these observations, heat index was set to NA.")
}
if (temperature.metric == "celsius") {
t <- celsius.to.fahrenheit(t)
}
hi <- unlist(.mapply(heat.index.algorithm, dots=list(t, rh), MoreArgs=NULL))
if (output.metric == "celsius") {
hi <- fahrenheit.to.celsius(hi)
}
hi <- round(hi, digits = round)
return(hi)
}
#' Algorithm for heat.index function.
#'
#' \code{heat.index.algorithm} converts a numeric scalar of temperature
#' (in Fahrenheit) and a numeric scalar of relative humidity (in \%)
#' to heat index (in Fahrenheit). This function is not meant to be used
#' outside of the \code{\link{heat.index}} function.
#'
#' @param t Numeric scalar of air temperature, in Fahrenheit.
#' @param rh Numeric scalar of relative humidity, in \%.
#'
#' @details If an impossible value of relative humidity is given
#' (below 0\% or above 100\%), heat index is returned as \code{NA}.
#'
#' @return A numeric scalar of heat index, in Fahrenheit.
#'
#' @note Equations are from the source code for the US National Weather
#' Service's
#' \href{http://www.wpc.ncep.noaa.gov/html/heatindex.shtml}{online heat index calculator}.
#'
#' @author
#' Brooke Anderson \email{brooke.anderson@@colostate.edu},
#' Roger Peng \email{rdpeng@@gmail.com}
#'
#' @references
#' Anderson GB, Bell ML, Peng RD. 2013. Methods to calculate the heat index
#' as an exposure Metric in environmental health research.
#' Environmental Health Perspectives 121(10):1111-1119.
#'
#' National Weather Service Hydrometeorological Prediction
#' Center Web Team. Heat Index Calculator. 30 Jan 2015.
#' \url{http://www.wpc.ncep.noaa.gov/html/heatindex.shtml}.
#' Accessed 18 Dec 2015.
#'
#' Rothfusz L. 1990. The heat index (or, more than you ever wanted to know
#' about heat index) (Technical Attachment SR 90-23). Fort Worth:
#' Scientific Services Division, National Weather Service.
#'
#' R. Steadman, 1979. The assessment of sultriness. Part I: A
#' temperature-humidity index based on human physiology and clothing
#' science. Journal of Applied Meteorology, 18(7):861--873.
#'
#' @seealso \code{\link{heat.index}}
#'
#' @export
heat.index.algorithm <-
function (t = NA, rh = NA)
{
if (is.na(rh) || is.na(t)) {
hi <- NA
} else if (t <= 40) {
hi <- t
} else {
alpha <- 61 + ((t - 68) * 1.2) + (rh * 0.094)
hi <- 0.5*(alpha + t)
if (hi > 79) {
hi <- -42.379 + 2.04901523 * t + 10.14333127 * rh -
0.22475541 * t * rh - 6.83783 * 10^-3 * t^2 -
5.481717 * 10^-2 * rh^2 + 1.22874 * 10^-3 * t^2 *
rh + 8.5282 * 10^-4 * t * rh^2 - 1.99 * 10^-6 *
t^2 * rh^2
if (rh <= 13 && t >= 80 && t <= 112) {
adjustment1 <- (13 - rh)/4
adjustment2 <- sqrt((17 - abs(t - 95))/17)
total.adjustment <- adjustment1 * adjustment2
hi <- hi - total.adjustment
} else if (rh > 85 && t >= 80 && t <= 87) {
adjustment1 <- (rh - 85)/10
adjustment2 <- (87 - t)/5
total.adjustment <- adjustment1 * adjustment2
hi <- hi + total.adjustment
}
}
}
return(hi)
}
geanders/weathermetrics documentation built on May 17, 2019, 12:14 a.m.
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#' Calculate heat index.
#'
#' \code{heat.index} creates a numeric vector of heat index values from
#' numeric vectors of air temperature and either relative humidity or
#' dew point temperature.
#'
#' @param t Numeric vector of air temperatures.
#' @param dp Numeric vector of dew point temperatures.
#' @param rh Numeric vector of relative humidity (in \%).
#' @param temperature.metric Character string indicating the temperature
#' metric of air temperature and dew point temperature. Possible values
#' are 'fahrenheit' or 'celsius'.
#' @param output.metric Character string indicating the metric into which
#' heat index should be calculated. Possible values are 'fahrenheit' or
#' 'celsius'.
#' @param round Integer indicating the number of decimal places to
#' round converted value.
#'
#' @details Include air temperature (\code{t}) and either dew point
#' temperature (\code{dp}) or relative humdity (\code{rh}). You cannot
#' specify both dew point temperature and relative humidity-- this will
#' return an error. Heat index is calculated as \code{NA} when impossible
#' values of dew point temperature or humidity are input (e.g., humidity
#' above 100\% or below 0\%, dew point temperature above air temperature).
#'
#' @return A numeric vector of heat index values in the metric specified
#' by \code{output.metric}. (If \code{output.metric} is not specified,
#' heat index will be returned in the same metric in which air
#' temperature was input, specified by \code{temperature.metric}.)
#'
#' @note Equations are from the source code for the US National Weather
#' Service's
#' \href{http://www.wpc.ncep.noaa.gov/html/heatindex.shtml}{online heat index calculator}.
#'
#' @author
#' Brooke Anderson \email{brooke.anderson@@colostate.edu},
#' Roger Peng \email{rdpeng@@gmail.com}
#'
#' @references
#' Anderson GB, Bell ML, Peng RD. 2013. Methods to calculate the heat index
#' as an exposure metric in environmental health research.
#' Environmental Health Perspectives 121(10):1111-1119.
#'
#' National Weather Service Hydrometeorological Prediction
#' Center Web Team. Heat Index Calculator. 30 Jan 2015.
#' \url{http://www.wpc.ncep.noaa.gov/html/heatindex.shtml}.
#' Accessed 18 Dec 2015.
#'
#' Rothfusz L. 1990. The heat index (or, more than you ever wanted to know
#' about heat index) (Technical Attachment SR 90-23). Fort Worth:
#' Scientific Services Division, National Weather Service.
#'
#' R. Steadman, 1979. The assessment of sultriness. Part I: A
#' temperature-humidity index based on human physiology and clothing
#' science. Journal of Applied Meteorology, 18(7):861--873.
#'
#' @examples # Calculate heat index from temperature (in Fahrenheit)
#'# and relative humidity.
#'
#' data(suffolk)
#'suffolk$heat.index <- heat.index(t = suffolk$TemperatureF,
#' rh = suffolk$Relative.Humidity)
#'suffolk
#'
#'# Calculate heat index (in Celsius) from temperature (in
#'# Celsius) and dew point temperature (in Celsius).
#'
#'data(lyon)
#'lyon$heat.index <- heat.index(t = lyon$TemperatureC,
#' dp = lyon$DewpointC,
#' temperature.metric = 'celsius',
#' output.metric = 'celsius')
#'lyon
#'
#' @export
heat.index <-
function (t = NA, dp = c(), rh = c(), temperature.metric = "fahrenheit",
output.metric = NULL, round = 0)
{
if(length(output.metric) == 0){
output.metric <- temperature.metric
}
if (length(dp) == 0 && length(rh) == 0) {
stop("You must give values for either dew point temperature ('dp') or relative humidity ('rh').")
}
else if (length(dp) > 0 && length(rh) > 0) {
stop("You can give values for either dew point temperature ('dp') or relative humidity ('rh'), but you cannot specify both to this function.")
}
if (length(dp) != length(t) && length(rh) != length(t)) {
stop("The vectors for temperature ('t') and moisture (either relative humidity, 'rh', or dew point temperature, 'dp') must be the same length.")
}
if (length(dp) > length(rh)) {
rh <- dewpoint.to.humidity(t = t, dp = dp, temperature.metric = temperature.metric)
}
else if (any(!is.na(rh) & (rh > 100 | rh < 0))) {
rh[!is.na(rh) & (rh > 100 | rh < 0)] <- NA
warning("There were observations with an impossible values for relative humidity (below 0% or above 100%). For these observations, heat index was set to NA.")
}
if (temperature.metric == "celsius") {
t <- celsius.to.fahrenheit(t)
}
hi <- unlist(.mapply(heat.index.algorithm, dots=list(t, rh), MoreArgs=NULL))
if (output.metric == "celsius") {
hi <- fahrenheit.to.celsius(hi)
}
hi <- round(hi, digits = round)
return(hi)
}
#' Algorithm for heat.index function.
#'
#' \code{heat.index.algorithm} converts a numeric scalar of temperature
#' (in Fahrenheit) and a numeric scalar of relative humidity (in \%)
#' to heat index (in Fahrenheit). This function is not meant to be used
#' outside of the \code{\link{heat.index}} function.
#'
#' @param t Numeric scalar of air temperature, in Fahrenheit.
#' @param rh Numeric scalar of relative humidity, in \%.
#'
#' @details If an impossible value of relative humidity is given
#' (below 0\% or above 100\%), heat index is returned as \code{NA}.
#'
#' @return A numeric scalar of heat index, in Fahrenheit.
#'
#' @note Equations are from the source code for the US National Weather
#' Service's
#' \href{http://www.wpc.ncep.noaa.gov/html/heatindex.shtml}{online heat index calculator}.
#'
#' @author
#' Brooke Anderson \email{brooke.anderson@@colostate.edu},
#' Roger Peng \email{rdpeng@@gmail.com}
#'
#' @references
#' Anderson GB, Bell ML, Peng RD. 2013. Methods to calculate the heat index
#' as an exposure Metric in environmental health research.
#' Environmental Health Perspectives 121(10):1111-1119.
#'
#' National Weather Service Hydrometeorological Prediction
#' Center Web Team. Heat Index Calculator. 30 Jan 2015.
#' \url{http://www.wpc.ncep.noaa.gov/html/heatindex.shtml}.
#' Accessed 18 Dec 2015.
#'
#' Rothfusz L. 1990. The heat index (or, more than you ever wanted to know
#' about heat index) (Technical Attachment SR 90-23). Fort Worth:
#' Scientific Services Division, National Weather Service.
#'
#' R. Steadman, 1979. The assessment of sultriness. Part I: A
#' temperature-humidity index based on human physiology and clothing
#' science. Journal of Applied Meteorology, 18(7):861--873.
#'
#' @seealso \code{\link{heat.index}}
#'
#' @export
heat.index.algorithm <-
function (t = NA, rh = NA)
{
if (is.na(rh) || is.na(t)) {
hi <- NA
} else if (t <= 40) {
hi <- t
} else {
alpha <- 61 + ((t - 68) * 1.2) + (rh * 0.094)
hi <- 0.5*(alpha + t)
if (hi > 79) {
hi <- -42.379 + 2.04901523 * t + 10.14333127 * rh -
0.22475541 * t * rh - 6.83783 * 10^-3 * t^2 -
5.481717 * 10^-2 * rh^2 + 1.22874 * 10^-3 * t^2 *
rh + 8.5282 * 10^-4 * t * rh^2 - 1.99 * 10^-6 *
t^2 * rh^2
if (rh <= 13 && t >= 80 && t <= 112) {
adjustment1 <- (13 - rh)/4
adjustment2 <- sqrt((17 - abs(t - 95))/17)
total.adjustment <- adjustment1 * adjustment2
hi <- hi - total.adjustment
} else if (rh > 85 && t >= 80 && t <= 87) {
adjustment1 <- (rh - 85)/10
adjustment2 <- (87 - t)/5
total.adjustment <- adjustment1 * adjustment2
hi <- hi + total.adjustment
}
}
}
return(hi)
}
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