SPIGA (version 1.0.0)

Drought Index from Parameters: Calculation of standardized precipitation index from alpha and beta parameter of the Gamma function.

Description

calculate the standardized precipitation index, from alpha and beta parameter of the Gamma function.

Usage

SPIFromParameters(Pmon, scale =3, Param_Alpha, Param_Beta)

Arguments

Pmon

monthly precipitation series ordered according to time. It is a data frame with columns: year, month, station 1, station 2, etc.

scale

an integer value representing the time scale of analysis. The most common are 1, 3, 6, 9, 12, 48, etc.

Param_Alpha

data frame monthly data values corresponding to the alpha parameter to the function Gamma.

Param_Beta

data frame monthly data values corresponding to the alpha parameter to the function Gamma.

Value

return values of standardized precipitation index in .txt formats.

Details

Analysis stations are in the columns of dataframe. the apha and beta parameters, are monthly and are in the rows of dataframe.

Input data similar to Pm_Pisco.

Mon	st_1	st_1	st_2
st_3	Jan	9.584860915	9.227918987
10.35269003	8.433823824	Feb	13.76378505
15.02620223	12.1021093	10.85133914	Mar
26.09112343	17.41749632	21.10924889	23.53649421
Apr	17.34996675	17.4451073	13.00894394
16.66595319	May	9.943259493	9.46815537
9.164645239	9.455850664	Jun	5.103175852
5.041710686	4.080851346	5.790986084	Jul
2.85804336	3.042484994	2.797962575	2.645188236
Aug	3.033862506	3.183267843	3.435303986
2.631287947	Sep	3.815308513	2.627317533
3.550365645	3.66482456	Oct	7.430925356
3.956716609	7.023105167	7.540706878	Nov
6.303310502	5.339943557	6.358902249	5.556660824
Dec	5.84110559	5.899534971	6.581657735
4.889599504	Mon	st_1	st_1

References

McKee, Thomas B. and Doesken, Nolan J. and Kleist, John. 1993. The relationship of Drought Frecuency and Duration to Time Scales. Eighth Conference on Applied Climatology

A. Belauneh and J. Adamowski. Standard Precipitation Index Drought Forecasting Using Neural Networks, Wavelet Neural Networks, and Support Vector Regression. Applied Computational Intelligence and Soft Computing, http://dx.doi.org/10.1155/2012/794061

Examples

#### Load data
data(Pm_Pisco)
data(alphaGA_SPI3)
data(betaGA_SPI3)

#### Computing SPI with Genetic Algorithms
Pmon<-Pm_Pisco
Param_Alpha <- alphaGA_SPI3
Param_Beta <- betaGA_SPI3
SPIFromParameters(Pmon, scale =3, Param_Alpha, Param_Beta)