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Calculate rolling Degree Heating Months

calculate_dhm.Rd

Implements the monthly heat-stress algorithm used by Mason, Bozec and Mumby (2025) and the supplied reference MATLAB script. Monthly SST anomalies above an externally defined MMM are accumulated over three or four months.

Usage

calculate_dhm(
  sst,
  mmm,
  window = 3L,
  threshold = 0,
  input = c("monthly", "daily"),
  conversion = c("none", "weekly_4", "weekly_4.35"),
  alignment = c("matlab_previous", "right"),
  output = c("rolling", "annual_max"),
  incomplete = c("missing", "matlab_zero"),
  min_month_coverage = 1,
  filename = "",
  overwrite = FALSE,
  wopt = list()
)

Arguments

sst

Monthly or daily SST terra::SpatRaster.

mmm

A one-layer externally defined Maximum Monthly Mean raster aligned with sst. For the Mason comparison this is the 1985–2000 observational MMM, not an MMM estimated from the evaluation period.

window

Rolling accumulation window in months, normally 3 or 4.

threshold

Minimum anomaly above MMM required for inclusion. The reference DHM uses 0; its sensitivity analysis also used 1.

input

Input resolution, "monthly" or "daily".

conversion

Output conversion. "none" returns degree C-months; "weekly_4" and "weekly_4.35" convert to approximate degree C-weeks.

alignment

"matlab_previous" assigns the previous complete window to the following month, exactly matching Calculate_DHW_or_DHM.m. "right" assigns a window to its final included month.

output

Return the monthly "rolling" series or "annual_max".

incomplete

"missing" marks dates without a complete history as NA. "matlab_zero" reproduces the MATLAB script's zero-initialized DHP matrix exactly.

min_month_coverage

For daily input, the minimum fraction of expected daily values required for a monthly mean.

filename

Optional output filename.

overwrite

Overwrite an existing output file.

wopt

Write options passed to terra::writeRaster().

Value

A rolling monthly or annual-maximum terra::SpatRaster.

References

Mason, R.A.B., Bozec, Y.-M. & Mumby, P.J. (2025), Nature Geoscience 18, 120–123. doi:10.1038/s41561-024-01635-7