A set of functions for computing potential evapotranspiration and several widely used drought indices including the Standardized Precipitation-Evapotranspiration Index (SPEI).
Functions spei and spi are the workhorse of the SPEI library. Other functions such as kern, cdfglo or pglo are auxiliary low-level functions and they will not be used directly by the typical user. Functions for computing potential evapotranspiration are provided, too, for helping computing the SPEI. They are: thornthwaite, hargreaves and penman.
Version history:
1.4. Minor fixes to functions penman and pwm. Documentation of the penman function defined by mistake ed as the saturation vapour pressure, while it should read 'actual vapour pressure'. Function zzz.R added to display basic information about the SPEI package at startup. Function SPEINews added to display the NEWS file.
1.3. Minor fixes to spei and penman functions. New option for user-supplied SPEI parameters in the spei function. New dataset cabinda.
1.2. A bug causing several functions to fail when a time series not belonging to matrix class was provided was fixed. Function plot.spei now distinguises between calls to spei and spi and labels the axis accordingly .
1.1. Functions spei and spi now yield an object of class "spei". New functions for summarizing and plotting "spei" objects are provided. An option to establish a reference period for the computation of the indices has been implemented in functions spei and spi.
1.0. First release.
S.M. Vicente-Serrano, S. Beguer<U+00ED>a, J.I. L<U+00F3>pez-Moreno. 2010. A Multi-scalar drought index sensitive to global warming: The Standardized Precipitation Evapotranspiration Index <U+2013> SPEI. Journal of Climate 23: 1696, DOI: 10.1175/2009JCLI2909.1.
http://sac.csic.es/spei/