Calculation of the Standardised Precipitation-Evapotranspiration Index

A set of functions for computing potential evapotranspiration and several widely used drought indices including the Standardized Precipitation-Evapotranspiration Index (SPEI).


__Version history:

_Version 1.6, September 2013.

  1. Corrected an error in the function \code{\link{thornthwaite}} which resulted in wrong potential evapotranspiration estimates when a multivariate time series was used as input.
  2. Corrected an error in the function \code{\link{spi}} which resulted in wrong handling of zero precipitation months when using the Gamma or PearsonIII distribution.
  3. Minor fixes to the \code{\link{spi}} and \code{\link{plot.spei}} functions to correctly handle \code{spei} objects when they result from a call to \code{\link{spi}}.
  4. Modification to the \code{\link{kern}} function, which now yields kernel coefficients averaging one.
  5. Corrected an error in the functions \code{\link{spi}} and \code{\link{spei}} which resulted in ub-pwm method being used irrespective of the value of the \code{fit} parameter used, when using the 'Gamma' or 'PearsonIII' distributions.
  6. Minor changes to the documentation.

_Version 1.5, May 2013.

  1. Optimization of function \code{\link{spei}}, now using embed() for accumulating the data at the desired time scale.

_Version 1.4, May 2013.

  1. Minor fixes to functions \code{\link{penman}} and \code{\link{pwm}}.
  2. Documentation of the penman function defined by mistake ed as the saturation vapour pressure, while it should read 'actual vapour pressure'.
  3. Function zzz.R added to display basic information about the SPEI package at startup.
  4. Function \code{\link{SPEINews}} added to display the NEWS file.

_Version 1.3, March 2013.

  1. Minor fixes to functions \code{\link{spei}} and \code{\link{penman}}.
  2. Added new option for user-supplied SPEI parameters in the \code{\link{spei}} function. This overrides the fitting of a probability function to the data.
  3. Added new dataset \code{\link{cabinda}} from Allen et al. (1998).

_Version 1.2, October 2012.

  1. Fixed a bug causing several functions to fail when a time series not belonging to matrix class was provided.
  2. Function \code{\link{plot.spei}} now distinguises between calls to spei and spi and labels the axis accordingly.

_Version 1.1, March 2012.

  1. Functions \code{\link{spei}} and \code{\link{spi}} now yield an object of class "spei".
  2. New functions for summarizing and plotting "spei" objects are provided.
  3. An option to establish a reference period for the computation of the indices has been implemented in functions \code{\link{spei}} and \code{\link{spi}}.

_Version 1.0, January 2012. First release of the SPEI package.

__To do (work in progress):

  1. Complete documentation for pwmLC.Rd.
  2. Review method plot.spei() that produces wrong results in some cases.
  3. Implement parallel processing.
  4. Analysis functions.

Reference manual

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1.7 by Santiago Beguería, 4 months ago

Browse source code at

Authors: Santiago Beguería [aut, cre], Sergio M. Vicente-Serrano [aut]

Documentation:   PDF Manual  

GPL-2 license

Depends on lmomco, parallel, ggplot2

See at CRAN