ck_ehf: Excess Heat Factor (EHF, Nairn & Fawcett 2013)

In climatekit: Unified Climate Indices for Temperature, Precipitation, and Drought

Excess Heat Factor (EHF, Nairn & Fawcett 2013)

Description

Annual summary of the daily Excess Heat Factor heatwave intensity metric. EHF combines a 3-day mean daily temperature anomaly above the 95th percentile of the reference period with an acclimatisation term (3-day mean minus previous 30-day mean). Positive EHF days indicate heatwave conditions; larger values indicate more severe or less-acclimatised events. This is the operational heatwave metric used by the Australian Bureau of Meteorology.

Usage

ck_ehf(
  tmax,
  tmin,
  dates,
  ref_start = 1961L,
  ref_end = 1990L,
  stat = c("max", "n_positive", "sum_positive")
)

Arguments

tmax	Numeric vector of daily maximum temperatures (degrees C).
tmin	Numeric vector of daily minimum temperatures (degrees C).
dates	Date vector of the same length as tmax. Must contain data covering the reference period.
ref_start, ref_end	Integer. Reference period boundary years (inclusive). Defaults to 1961 and 1990.
stat	One of "max", "n_positive", or "sum_positive".

Details

Three annual summaries are exposed via the stat argument:

• "max" (default): peak EHF in the year. Strongest single-day intensity.

• "n_positive": count of days with EHF > 0. A frequency-of-heatwave-conditions measure.

• "sum_positive": sum of EHF on days with EHF > 0. A severity-weighted total.

Value

A data frame with columns period, value, index, and unit.

References

Nairn, J. R., & Fawcett, R. J. B. (2013). Defining heatwaves: heatwave defined as a heat-impact event servicing all community and business sectors in Australia. CAWCR Technical Report No. 060.

Perkins, S. E., & Alexander, L. V. (2013). On the measurement of heatwaves. Journal of Climate, 26(13), 4500-4517. \Sexpr[results=rd]{tools:::Rd_expr_doi("10.1175/JCLI-D-12-00383.1")}.

Examples

set.seed(1)
dates <- seq(as.Date("1961-01-01"), as.Date("1991-12-31"), by = "day")
s <- 2 * pi * as.integer(format(dates, "%j")) / 365
tmax <- 20 + 10 * sin(s) + rnorm(length(dates))
tmin <- 10 +  8 * sin(s) + rnorm(length(dates))
tail(ck_ehf(tmax, tmin, dates))

climatekit documentation built on May 9, 2026, 5:08 p.m.