When I was doing this work first I based myself on the wmo book Standardized Precipitation Index User Guide, and this book explains how to do it but we need a data series up to at least 10 years of accumulated precipitation, with the program or software recommended by wmo you can do the SPi calculations, according to McKee

Yes I also used the wmo book for computation of SPI but the software recommended by WMO uses data in text or excel files and not netcdf files. Moreover the WMO sofware use location specific data and what I want is tgo compute SPI at different grid point for the entire African continent.

I see, so it gets a little difficult, but I will try to investigate further to be able to help you if it is appropriate, but I can't promise.

I think this help you: https://www.youtube.com/watch?v=8iGqDgBdBFU

Thank you very much for the link, the information in the video is very nice. I am struggling how to install ncl in the window machine. I would appreciate if you have step by step way of installing the ncl in window. Yest I know I need to install cygwin 86exe, but something challening me is the packages and libraries required for the analysis

right, I use WSL linux on windows and already have it installed in the python package, but you can watch some videos on youtube and investigate how to install NCL on windows.

I think this help you: https://www.youtube.com/watch?v=eaVU_7RWu34

thank you I managed to install NCL and able to compute all SPI from netcdf files, I appreciate for your interest to help

Good morning my friend, I share with u, this slide.

Thank you for sharing.