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i.evapo.pt

Computes evapotranspiration calculation Priestley and Taylor formulation, 1972.

i.evapo.pt [-z] net_radiation=name soil_heatflux=name air_temperature=name atmospheric_pressure=name priestley_taylor_coeff=float output=name [--overwrite] [--verbose] [--quiet] [--qq] [--ui]

Example:

i.evapo.pt net_radiation=name soil_heatflux=name air_temperature=name atmospheric_pressure=name priestley_taylor_coeff=1.26 output=name

grass.script.run_command("i.evapo.pt", net_radiation, soil_heatflux, air_temperature, atmospheric_pressure, priestley_taylor_coeff=1.26, output, flags=None, overwrite=None, verbose=None, quiet=None, superquiet=None)

Example:

gs.run_command("i.evapo.pt", net_radiation="name", soil_heatflux="name", air_temperature="name", atmospheric_pressure="name", priestley_taylor_coeff=1.26, output="name")

grass.tools.Tools.i_evapo_pt(net_radiation, soil_heatflux, air_temperature, atmospheric_pressure, priestley_taylor_coeff=1.26, output, flags=None, overwrite=None, verbose=None, quiet=None, superquiet=None)

Example:

tools = Tools()
tools.i_evapo_pt(net_radiation="name", soil_heatflux="name", air_temperature="name", atmospheric_pressure="name", priestley_taylor_coeff=1.26, output="name")

This grass.tools API is experimental in version 8.5 and expected to be stable in version 8.6.

Parameters

net_radiation=name [required]
    Name of input net radiation raster map [W/m2]
soil_heatflux=name [required]
    Name of input soil heat flux raster map [W/m2]
air_temperature=name [required]
    Name of input air temperature raster map [K]
atmospheric_pressure=name [required]
    Name of input atmospheric pressure raster map [millibars]
priestley_taylor_coeff=float [required]
    Priestley-Taylor coefficient
    Default: 1.26
output=name [required]
    Name of output evapotranspiration raster map [mm/d]
-z
    Set negative ETa to zero
--overwrite
    Allow output files to overwrite existing files
--help
    Print usage summary
--verbose
    Verbose module output
--quiet
    Quiet module output
--qq
    Very quiet module output
--ui
    Force launching GUI dialog

net_radiation : str, required
    Name of input net radiation raster map [W/m2]
    Used as: input, raster, name
soil_heatflux : str, required
    Name of input soil heat flux raster map [W/m2]
    Used as: input, raster, name
air_temperature : str, required
    Name of input air temperature raster map [K]
    Used as: input, raster, name
atmospheric_pressure : str, required
    Name of input atmospheric pressure raster map [millibars]
    Used as: input, raster, name
priestley_taylor_coeff : float, required
    Priestley-Taylor coefficient
    Default: 1.26
output : str, required
    Name of output evapotranspiration raster map [mm/d]
    Used as: output, raster, name
flags : str, optional
    Allowed values: z
    z
        Set negative ETa to zero
overwrite : bool, optional
    Allow output files to overwrite existing files
    Default: None
verbose : bool, optional
    Verbose module output
    Default: None
quiet : bool, optional
    Quiet module output
    Default: None
superquiet : bool, optional
    Very quiet module output
    Default: None

net_radiation : str | np.ndarray, required
    Name of input net radiation raster map [W/m2]
    Used as: input, raster, name
soil_heatflux : str | np.ndarray, required
    Name of input soil heat flux raster map [W/m2]
    Used as: input, raster, name
air_temperature : str | np.ndarray, required
    Name of input air temperature raster map [K]
    Used as: input, raster, name
atmospheric_pressure : str | np.ndarray, required
    Name of input atmospheric pressure raster map [millibars]
    Used as: input, raster, name
priestley_taylor_coeff : float, required
    Priestley-Taylor coefficient
    Default: 1.26
output : str | type(np.ndarray) | type(np.array) | type(gs.array.array), required
    Name of output evapotranspiration raster map [mm/d]
    Used as: output, raster, name
flags : str, optional
    Allowed values: z
    z
        Set negative ETa to zero
overwrite : bool, optional
    Allow output files to overwrite existing files
    Default: None
verbose : bool, optional
    Verbose module output
    Default: None
quiet : bool, optional
    Quiet module output
    Default: None
superquiet : bool, optional
    Very quiet module output
    Default: None

Returns:

result : grass.tools.support.ToolResult | np.ndarray | tuple[np.ndarray] | None
If the tool produces text as standard output, a ToolResult object will be returned. Otherwise, None will be returned. If an array type (e.g., np.ndarray) is used for one of the raster outputs, the result will be an array and will have the shape corresponding to the computational region. If an array type is used for more than one raster output, the result will be a tuple of arrays.

Raises:

grass.tools.ToolError: When the tool ended with an error.

DESCRIPTION

i.evapo.pt Calculates the diurnal evapotranspiration after Prestley and Taylor (1972). The Priestley-Taylor model (Priestley and Taylor, 1972) is a modification of Penman's more theoretical equation.

NOTES

RNETD optional output from i.evapo.potrad is giving good results as input for net radiation in this module.

Alpha values:

  • 1.32 for estimates from vegetated areas as a result of the increase in surface roughness (Morton, 1983; Brutsaert and Stricker, 1979)
  • 1.26 is applicable in humid climates (De Bruin and Keijman, 1979; Stewart and Rouse, 1976; Shuttleworth and Calder, 1979), and temperate hardwood swamps (Munro, 1979)
  • 1.74 has been recommended for estimating potential evapotranspiration in more arid regions (ASCE, 1990). This worked well in Greece with University of Thessaloniki.

Alpha values extracted from: Watflood manual.

SEE ALSO

i.evapo.mh, i.evapo.pm, i.evapo.time, i.eb.netrad, r.sun

AUTHOR

Yann Chemin, GRASS Development Team, 2007-08

SOURCE CODE

Available at: i.evapo.pt source code (history)
Latest change: Thursday Jun 26 21:25:27 2025 in commit 3ec2b13