UKFE (version 1.0.2)

POTt: Peaks over threshold (POT) data extraction (quick)

Description

Extracts independent peaks over a threshold from a sample, using time as the independence criteria.

Usage

POTt(
  x,
  threshold = 0.975,
  div,
  Plot = TRUE,
  PlotType = "l",
  main = "Peaks over threhsold",
  ylab = "Magnitude",
  xlab = "Time"
)

Value

A data.frame with columns; Date and peak, with the option of a plot. Or a numeric vector of peaks is returned if only a numeric vector of the variable is input as x.

Arguments

x

either a numeric vector or dataframe with date (or POSIXct) in the first column and hydrological variable in the second

threshold

user chosen threshold. Default is 0.975

div

number of time steps between peaks to ensure independence.

Plot

logical argument with a default of TRUE. When TRUE, the full hydrograph with the peaks over the threshold highlighted is plotted

PlotType

Type of plot with a default of "l" for line graph. For rainfall type "h" for bars could be used.

main

Title for the plot. Default is "Peaks over threshold"

ylab

Label (character) for the plot y axis. Default is "Magnitude"

xlab

Label (character) for the plot x axis. Default is "Time".

Author

Anthony Hammond

Details

This provides a quicker option than the POTextract function - useful for very long time series'. It only has the option of time division to ensure independence between peaks. If the x argument is a numeric vector, the peaks will be extracted with no time information. x can instead be a data.frame with dates in the first column and the numeric vector in the second. In this latter case, the peaks will be time-stamped and a hydrograph, including POT, will be plotted by default.

Examples

# Extract POT data from Thames catchment daily rainfall 2000-10-01 to 2015-09-30 with
# div = 14 (14 days) and threshold = 0.975, and display the first six rows
thames_p_pot <- POTt(ThamesPQ[, c(1, 2)], div = 14, threshold = 0.975)
head(thames_p_pot)

# Extract Thames rainfall POT from the numeric vector of rainfall, with threshold
# set to 0.95 and div set to 14, and display the first six rows
thames_p_pot <- POTt(ThamesPQ[, 2], threshold = 0.95, div = 14)
head(thames_p_pot)