calc_timingLow: Indices describing timing of low flow events.

In USGS-R/EflowStats: Hydrologic Indicator and Alteration Stats

Indices describing timing of low flow events.

Description

Calculates 3 indices used to describe the timing of high flow conditions. See Table X in the EflowStats package vignette for a full description of indices.

Usage

calc_timingLow(
  x,
  yearType = "water",
  wyMonth = 10L,
  digits = 3,
  pref = "mean",
  floodThreshold = NULL,
  ...
)

Arguments

x	A dataframe containing a vector of date values in the first column and vector of numeric flow values in the second column.
yearType	A charcter of either "water" or "calendar" indicating whether to use water years or calendar years, respectively.
wyMonth	A numeric. The month of the year in which the water year starts (1=January, 12=December). The water year begins on the first day of wyMonth.
digits	A numeric. Number of digits to round indice values
pref	A character of either "mean" or "median", indicating whether to use mean or median. See details.
floodThreshold	Numeric flood threshold as the flow equivalent for a flood recurrence of 1.67 years
...	Optional arguments needed for calc_allHIT function

Details

Descriptions of indices.

• tl1; Julian date of annual minimum. Determine the Julian date that the minimum flow occurs for each water year. Transform the dates to relative values on a circular scale (radians or degrees). Compute the x and y components for each year and average them across all years. Compute the mean angle as the arc tangent of y-mean divided by x-mean. Transform the resultant angle back to Julian date.

• tl2 Variability in Julian date of annual minima. Compute the coefficient of variation for the mean x and y components and convert to a date.

• tl3 Seasonal predictability of low flow. Divide years up into 2-month periods (that is, Oct-Nov, Dec-Jan, and so forth). Count the number of low flow events (flow events with flows <= 5 year flood threshold) in each period over the entire flow record. TL3 is the maximum number of low flow events in any one period divided by the total number of low flow events.

• tl4 Seasonal predictability of non-low flow. Compute the number of days that flow is above the 5-year flood threshold as the ratio of number of days to 365 or 366 (leap year) for each year. TL4 is the maximum of the yearly ratios.

Note: In these definitions, "Julian date" should be interpreted as the count of days starting with 1 on January first of a given year, ending at 365 or 366 on December 31st.

Value

A data.frame of flow statistics

Examples

x <- sampleData[c("date","discharge")]
yearType = "water"
floodThreshold = 1161.38
calc_timingLow(x=x,yearType=yearType,floodThreshold=floodThreshold)

USGS-R/EflowStats documentation built on Sept. 30, 2023, 9:31 p.m.