How to calculate Standard Precipitation Index (SPI) using ArcGIS

[hawfinchtaylor]

I am running through a big challenge to calculate Standard Precipitation Index (SPI) using raster images of precipitation(ftp://ftp.cpc.ncep.noaa.gov/fews/fewsdata/africa/rfe2/geotiff).

Is someone have any idea about GIS or remote sensing software or freely available tool or some code in IDL which could calculate SPI on rater images?

Please help me to solve this problem
Thanks

[fs1]

I am running through a big challenge to calculate Standard Precipitation Index (SPI) using raster images of precipitation(ftp://ftp.cpc.ncep.noaa.gov/fews/fewsdata/africa/rfe2/geotiff).

Is someone have any idea about GIS or remote sensing software or freely available tool or some code in IDL which could calculate SPI on rater images?

Please help me to solve this problem
Thanks

hello, I am equally interested in calculating the SPI index from raster. The only idea that occurs to me is to transform them into ascii format and calculate by R. If you get how to do it in Arcgis contact me through the platform.
a Fran greeting from Spain

[BennyIstanto]

Hi,

I have calculate the SPI using monthly CHIRPS CHG - Data (1981 - present).

Here's the step:

1. Calculate rainfall average and standard deviation by month (I used 1981 - 2014 as a base period), you can used Cell Statistics tool in the Spatial Analyst toolbox, and choose MEAN and STD to calculate the average and standard deviation for JAN, FEB, ..., DEC 1981 - 2014.

2. Calculate the SPI (example Jul 2015): SPI = (Rainfall Jul 2015 - Rainfall AVG Jul 1981-2014) / Standard Deviation of Rainfall in Jul 1981-2014

[helenkirubs]

tanks for a good idea but how to site your paper