FlexDroughtIndex is a package of functions in R that calculates different drought indices by means of a flexible procedure described in:
- Sergio M. Vicente-Serrano, Fergus Reig, Santiago Begueréa, Ahmed El-Kenawy, Fernando Domínguez-Castro, Magí Franquesa, Luis Gimeno-Sotelo, María Adell, Amar Halifa, Miguel Andres-Martin, Cesar Azorín-Molina: An optimal flexible approach to calculate standardized drought indices. Under review
It calculates the following drought indices:
- SPI: Standardized Precipitation Index
- SPEI: Standardized Precipitation Evapotranspiration Index
- SEDI: Standardized Evapotranspiration Deficit Index
Nevertheless, actually serves to standardize any data series that has different characteristics. For example, SPI would normalize any series truncated to 0 at the bottom, SEDI truncated at the top, and SPEI any series ranging from -inf to +inf. The functions have a fundamental advantage over previous approaches as the procedure uses the distribution that gives us a better normalized resulting series for each monthly (and scale) series according to the Shapiro-Wilks test of normality.
- SPI(series, scale, fr, ref.start = NULL, ref.end = NULL)
- scale is the time scale of the index
- fr is the frequency of the data. E.g., monthly series have a frequency of 12.
- ref.start and ref.end define the reference period for calculations.