PotentialEvapotranspiration: Compute potential evapotranspiration#

class PotentialEvapotranspiration(*args, **kwds)[source]#

Bases: Component

Potential Evapotranspiration Component calculates spatially distributed potential evapotranspiration based on input radiation factor (spatial distribution of incoming radiation) using chosen method such as constant or Priestley Taylor. Ref: Xiaochi et. al. 2013 for ‘Cosine’ method and ASCE-EWRI Task Committee Report Jan 2005 for ‘PriestleyTaylor’ method. Note: Calling ‘PriestleyTaylor’ method would generate/overwrite shortwave & longwave radiation fields.

Code author: Sai Nudurupati and Erkan Istanbulluoglu

Examples

>>> from landlab import RasterModelGrid
>>> from landlab.components.pet import PotentialEvapotranspiration
>>> grid = RasterModelGrid((5, 4), xy_spacing=(0.2, 0.2))
>>> grid['cell']['radiation__ratio_to_flat_surface'] = np.array([
...       0.38488566, 0.38488566,
...       0.33309785, 0.33309785,
...       0.37381705, 0.37381705])
>>> PET = PotentialEvapotranspiration(grid)
>>> PET.name
'PotentialEvapotranspiration'
>>> PET.input_var_names
('radiation__ratio_to_flat_surface',)
>>> sorted(PET.output_var_names)
['radiation__incoming_shortwave_flux',
 'radiation__net_flux',
 'radiation__net_longwave_flux',
 'radiation__net_shortwave_flux',
 'surface__potential_evapotranspiration_rate']
>>> sorted(PET.units) 
[('radiation__incoming_shortwave_flux', 'W/m^2'),
 ('radiation__net_flux', 'W/m^2'),
 ('radiation__net_longwave_flux', 'W/m^2'),
 ('radiation__net_shortwave_flux', 'W/m^2'),
 ('radiation__ratio_to_flat_surface', 'None'),
 ('surface__potential_evapotranspiration_rate', 'mm')]
>>> PET.grid.number_of_cell_rows
3
>>> PET.grid.number_of_cell_columns
2
>>> PET.grid is grid
True
>>> pet_rate = grid.at_cell['surface__potential_evapotranspiration_rate']
>>> np.allclose(pet_rate, 0.)
True
>>> PET.current_time = 0.5
>>> PET.update()
>>> np.allclose(pet_rate, 0.)
False

References

Required Software Citation(s) Specific to this Component

None Listed

Additional References

ASCE-EWRI: The ASCE standardized reference evapotranspiration equation, in: Standardization of Reference Evapotranspiration Task Committee Final Report, edited by: Allen, R. G., Walter, I. A., Elliot, R. L., Howell, T. A., Itenfisu, D., Jensen, M. E., and Snyder, R. L., Technical Committee report to the Environmental and Water Resources Institute of the American Society of Civil Engineers from the Task Committee on Standardization of Reference Evapotranspiration, Reston, VA, USA, 2005.

Zhou, X., Istanbulluoglu, E., and Vivoni, E. R.: Modeling the ecohydrological role of aspect-controlled radiation on tree-grass-shrub coexistence in a semiarid climate, Water Resour. Res., 49, 2872– 2895, doi:10.1002/wrcr.20259, 2013.

Parameters
  • grid (RasterModelGrid) – A grid.

  • method (required for 'MeasuredRadiationPT') – Priestley Taylor method will spit out radiation outputs too.

  • priestley_taylor_constant (float, optional) – Alpha used in Priestley Taylor method.

  • albedo (float, optional) – Albedo.

  • latent_heat_of_vaporization (float, optional) – Latent heat of vaporization for water Pwhv (Wd/(m*mm^2)).

  • psychometric_const (float, optional) – Psychometric constant (kPa (deg C)^-1).

  • stefan_boltzmann_const (float, optional) – Stefan Boltzmann’s constant (W/(m^2K^-4)).

  • solar_const (float, optional) – Solar constant (W/m^2).

  • latitude (float, optional) – Latitude (radians).

  • elevation_of_measurement (float, optional) – Elevation at which measurement was taken (m).

  • adjustment_coeff (float, optional) – adjustment coeff to predict Rs from air temperature (deg C)^-0.5.

  • lt (float, optional) – lag between peak TmaxF and solar forcing (days).

  • nd (float, optional) – Number of days in year (days).

  • MeanTmaxF (float, optional) – Mean annual rate of TmaxF (mm/d).

  • delta_d (float, optional) – Calibrated difference between max & min daily TmaxF (mm/d).

  • current_time (float, required only for 'Cosine' method) – Current time (Years)

  • const_potential_evapotranspiration (float, optional for) – ‘Constant’ method Constant PET value to be spatially distributed.

  • Tmin (float, required for 'Priestley Taylor' method) – Minimum temperature of the day (deg C)

  • Tmax (float, required for 'Priestley Taylor' method) – Maximum temperature of the day (deg C)

  • Tavg (float, required for 'Priestley Taylor' and 'MeasuredRadiationPT') – methods Average temperature of the day (deg C)

  • float (obs_radiation) – Observed radiation (W/m^2)

  • method – Observed radiation (W/m^2)

property Tavg#

Average temperature of the day (deg C)

Tavg: float, required for ‘Priestley Taylor’ and ‘MeasuredRadiationPT’ methods.

property Tmax#

Maximum temperature of the day (deg C)

Tmax: float, required for ‘Priestley Taylor’ method.

property Tmin#

Minimum temperature of the day (deg C)

Tmin: float, required for ‘Priestley Taylor’ method.

__init__(grid, method='Cosine', priestley_taylor_const=1.26, albedo=0.6, latent_heat_of_vaporization=28.34, psychometric_const=0.066, stefan_boltzmann_const=5.67e-08, solar_const=1366.67, latitude=34.0, elevation_of_measurement=300, adjustment_coeff=0.18, lt=0.0, nd=365.0, MeanTmaxF=12.0, delta_d=5.0, current_time=None, const_potential_evapotranspiration=12.0, Tmin=0.0, Tmax=1.0, Tavg=0.5, obs_radiation=350.0)[source]#
Parameters
  • grid (RasterModelGrid) – A grid.

  • method (required for 'MeasuredRadiationPT') – Priestley Taylor method will spit out radiation outputs too.

  • priestley_taylor_constant (float, optional) – Alpha used in Priestley Taylor method.

  • albedo (float, optional) – Albedo.

  • latent_heat_of_vaporization (float, optional) – Latent heat of vaporization for water Pwhv (Wd/(m*mm^2)).

  • psychometric_const (float, optional) – Psychometric constant (kPa (deg C)^-1).

  • stefan_boltzmann_const (float, optional) – Stefan Boltzmann’s constant (W/(m^2K^-4)).

  • solar_const (float, optional) – Solar constant (W/m^2).

  • latitude (float, optional) – Latitude (radians).

  • elevation_of_measurement (float, optional) – Elevation at which measurement was taken (m).

  • adjustment_coeff (float, optional) – adjustment coeff to predict Rs from air temperature (deg C)^-0.5.

  • lt (float, optional) – lag between peak TmaxF and solar forcing (days).

  • nd (float, optional) – Number of days in year (days).

  • MeanTmaxF (float, optional) – Mean annual rate of TmaxF (mm/d).

  • delta_d (float, optional) – Calibrated difference between max & min daily TmaxF (mm/d).

  • current_time (float, required only for 'Cosine' method) – Current time (Years)

  • const_potential_evapotranspiration (float, optional for) – ‘Constant’ method Constant PET value to be spatially distributed.

  • Tmin (float, required for 'Priestley Taylor' method) – Minimum temperature of the day (deg C)

  • Tmax (float, required for 'Priestley Taylor' method) – Maximum temperature of the day (deg C)

  • Tavg (float, required for 'Priestley Taylor' and 'MeasuredRadiationPT') – methods Average temperature of the day (deg C)

  • float (obs_radiation) – Observed radiation (W/m^2)

  • method – Observed radiation (W/m^2)

property const_potential_evapotranspiration#

Constant PET value to be spatially distributed.

Used by ‘Constant’ method.

property obs_radiation#

Observed radiation (W/m^2)

obs_radiation float, required for ‘MeasuredRadiationPT’ method.

update()[source]#

Update fields with current conditions.

If the ‘Constant’ method is used, this method looks to the value of the const_potential_evapotranspiration property.

If the ‘PriestleyTaylor’ method is used, this method looks to the values of the Tmin, Tmax, and Tavg properties.

If the ‘MeasuredRadiationPT’ method is use this method looks to the values of the Tavg and obs_radiation property.