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NAME

t.spei - Computes an EDO/EFFIS-style monthly SPEI drought-monitoring STRDS from precipitation and min/max temperature (via t.in.era5 if not already present), using Hargreaves PET and a log-logistic fit.

KEYWORDS

temporal, hydrology, climate, drought, fire

SYNOPSIS

t.spei
t.spei --help
t.spei [-c] start=string end=string [fit_start=string] [fit_end=string] [scales=integer[,integer,...]] [region=name] [precipitation=name] [temperature_min=name] [temperature_max=name] [pet=name] output_prefix=string [cache_dir=name] [area=north,west,south,east] [--help] [--verbose] [--quiet] [--ui]

Flags:

-c
Also produce a classified STRDS per scale (_speiclass) using the 7-class McKee (1993) drought severity scheme
--help
Print usage summary
--verbose
Verbose module output
--quiet
Quiet module output
--ui
Force launching GUI dialog

Parameters:

start=string [required]
Start date of the output monitoring period, YYYY-MM-DD
end=string [required]
End date of the output monitoring period, YYYY-MM-DD (inclusive)
fit_start=string
Start of the climatological calibration period used to fit the log-logistic distribution (default: 1991-01-01, the current WMO 30-year normal start)
Default: 1991-01-01
fit_end=string
End of the climatological calibration period (default: 2020-12-31, the current WMO 30-year normal end)
Default: 2020-12-31
scales=integer[,integer,...]
Accumulation scales in months (SPEI-1/3/6/12); SPEI-3 is the scale most commonly used as an EFFIS fire-risk/fuel-dryness input -- other EDO scales (2,9,24,48) can be added here
Default: 1,3,6,12
region=name
Named region to process into (g.region region=); default is the current computational region
precipitation=name
Existing precipitation STRDS (mm per day); if not given, imported via t.in.era5
temperature_min=name
Existing daily minimum 2m temperature STRDS (deg C); if not given, imported via t.in.era5
temperature_max=name
Existing daily maximum 2m temperature STRDS (deg C); if not given, imported via t.in.era5
pet=name
Existing potential evapotranspiration STRDS (mm per day), e.g. ERA5-Land's own potential_evaporation. If given, used directly for the water balance instead of computing Hargreaves PET, and temperature_min=/temperature_max= are not needed. Not fetched automatically -- EDO's own methodology uses Hargreaves, not a reanalysis model's internal PET (see NOTES in t.spei.md); this is an override for callers who already have a PET series and want to skip Hargreaves.
output_prefix=string [required]
STRDS name prefix; continuous output is <output_prefix>_spei<scale>, classified output (if -c) is <output_prefix>_speiclass<scale>
Default: spei
cache_dir=name
Directory to cache t.in.era5 downloads in (only used when precipitation=/temperature_min=/temperature_max= are not given); default a temporary directory
area=north,west,south,east
Bounding box in WGS84 degrees for t.in.era5 downloads (only used when the ERA5 inputs are not already given); default derived from the region

Table of contents

DESCRIPTION

t.spei computes monthly SPEI at one or more accumulation scales and registers each <output_prefix>_spei<scale> result as its own space-time raster dataset (STRDS), e.g. spei_spei3, spei_spei12, following the methodology used by JRC's European Drought Observatory (EDO) for the SPEI layers shown in the Copernicus EFFIS (European Forest Fire Information System) drought/fire-risk viewer:

If precipitation=, temperature_min= and temperature_max= are not given, the required STRDS are imported automatically via t.in.era5 -- pulling exactly the date range needed (the requested period, extended back far enough to cover the largest accumulation scale, and the calibration/ reference period if it extends further back).

SPEI-3 (3-month accumulation) is the scale most commonly used as a fuel-dryness/fire-risk input in EFFIS-style monitoring; other EDO scales (e.g. 2, 9, 24, 48 months) can be requested via scales=.

OPTIONS

temperature_min=/temperature_max= are auto-imported via t.in.era5 if omitted, and are not needed at all if pet= is given.

pet= is an existing potential evapotranspiration STRDS (mm/day), e.g. an already-imported ERA5-Land potential_evaporation STRDS. If given, it is used directly for the water balance instead of computing Hargreaves PET, and temperature_min=/temperature_max= are ignored. Unlike precipitation/temperature, pet= is never auto-fetched -- EDO's own SPEI methodology uses Hargreaves, not a reanalysis model's internal PET (see NOTES below); it exists purely as an override for callers who already have a PET series and want to bypass Hargreaves. Not giving pet= and not being able to resolve both temperature STRDS is a fatal error -- there is no third fallback.

CLASSIFICATION SCHEME (-c)

ClassLabelSPEI range
1Extremely dry<= -2.0
2Severely dry-2.0 to -1.5
3Moderately dry-1.5 to -1.0
4Near normal-1.0 to 1.0
5Moderately wet1.0 to 1.5
6Severely wet1.5 to 2.0
7Extremely wet>= 2.0

EXAMPLE

Monthly SPEI-1/3/6/12 over Portugal for the 2022-2023 fire seasons, calibrated against the 1991-2020 WMO normal, importing ERA5 data automatically, with classified output: 
g.region n=42 s=37 w=-9.6 e=-6.2 res=0:06

t.spei -c start=2022-01-01 end=2023-12-31 \
  fit_start=1991-01-01 fit_end=2020-12-31 \
  scales=1,3,6,12 \
  output_prefix=pt_effis cache_dir=$HOME/era5_cache

t.rast.list input=pt_effis_speiclass3
Using precipitation/temperature STRDS already in the mapset: 
t.spei start=2023-06-01 end=2023-09-30 scales=3 \
  precipitation=precip_daily temperature_min=tmin_daily temperature_max=tmax_daily \
  output_prefix=summer2023

NOTES

REQUIREMENTS

REFERENCES

SEE ALSO

r.latlong, t.create, t.drought, t.in.era5, t.register

AUTHOR

Yann Chemin

SOURCE CODE

Available at: t.spei source code (history)

Accessed: Sunday Sep 13 08:30:04 2026

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