SPEI

Luo_Suppe2026-08-15

gma.climet.index.SPEI

function SPEI(pre, pet, axis = None, scale = 1, periodicity = 12, distribution = "LogLogistic", fit_method = "LMoment", calibration = None):

Calculate the Standardized Precipitation Evapotranspiration Index.

Parameters:

pre: array.

Precipitation (mm).

pet: array.

Potential evapotranspiration (mm).

Optional:

axis = int. Default None.

Calculation axis. If not set (None), multidimensional data will be expanded to 1 dimension for calculation.

scale = int. Default 1.

Time scale. For example: 1, 3 or others.

periodicity = int. Default 12.

Periodicity of data. For example: the monthly scale can have a period of 12.

distribution = str. Default 'LogLogistic'.

Distribution type to be used for the internal fitting/transform computation.

Supported distributions include: 'Gamma', 'LogLogistic', 'Pearson3'.

fit_method = str. Default 'LMoment'.

Fitting methods for distribution parameters.

Supported method include: 'MLE': Maximum Likelihood Estimation, 'LMoment': L-Moment Estimation(PWD), 'LMoment2': L-Moment Estimation.

calibration = list||slice||None. Default None.

Fit the calibration interval of distribution parameter data, Based on the periodicity.

Default(None) using all data. For example: Select the data from 1-5 periodicity to fit parameters: calibration = [0, 5] Then apply the parameter fitting results to all data.

*Note: scale||periodicity||Calibrationarebasedoncalculatedaxis!.

Returns:

Type: array.

References.

Vicente-Serrano S M , S Beguer��a, JI L��pez-Moreno. A Multiscalar Drought Index.

Sensitive to Global Warming: TheStandardizedPrecipitationEvapotranspirationIndex[J].

Journal of Climate, 2010, 23(7): 1696-1718.