Follow these articles

Article Comparison of the Performance of Six Drought Indices in Char...

http://www.wamis.org/agm/meetings/wies09/S62-Khanna.pdf

It is good question to discuss

For calculation I recomend R using the SPEI - Package

https://cran.r-project.org/web/packages/SPEI/SPEI.pdf

You can performe:

SPEI Standardized Precipitation-Evapotranspiration Index

SPI Standardized Precipitation Index

Tutorial can be found her: Research HOW TO USE: Package 'SPEI' For BASIC CALCULATIONS

Agreeing with each other

Follow

Dear Das

You can easily calculate it with DMAP and MDM tools. If you want calculate SPI for middle-East by AgMERRA precipitation data with 0.25degree*0.25degree resolution, by using MDM tool you can compute SPI very soon an get Excel files for your outputs.

See the bellow links which are so useful and you can also customize your demand through the link.

If you have other questions let me know:

https://agrimetsoft.com/drought%20monitoring%20and%20prediction.aspx

https://agrimetsoft.com/MDM.aspx

Also, in DMAP you can as well calculate more than 18 drought indices. It is really easy and user-friendly.

Cheers,

Nasrin

There is several gauges that you can use it such as AgMerra, CPC, TRMM, Gleam, .... but the format of data in all gauges is netcdf and you can use Netcdf-Extractor and "Open NC File" for extract data from netcdf files. Also you can use Matlab, NCl, NCO, etc.

In other hands, there is a paper in researchgate that use AgMerra for calculating 8 drought indices.

https://www.researchgate.net/publication/320467560_Estimation_of_meteorological_drought_indices_based_on_AgMERRA_precipitation_data_and_station-observed_precipitation_data?_sg=_dTIOsm72WFWBCy2BJ6jmp3fXP8smwODTFeXonouxTyK5mbI14gSscVVR7kaDWPXf3QXSL_Bf4VO15CDCxcmccSG0AKCWW8ZR7h8QUhG.SGW6SUZ0X_Omgd-tetFG3aTxRjefb_7Pn4HytiZI0mcNgJiaKvgvM8Szw4nqigE-19RPNwv6XJW56t4tT5s5gA

and you can read this paper for knowing about 4 gauges.

Article Evaluation of different gridded rainfall datasets for rainfe...

This maybe useful for your needs: https://agrimetsoft.com/mdm.aspx

You can use R with SPEI package

or Drought Indices Calculator (DrinC) software ( http://drought-software.com/ )

Please follow this video. It is very useful.

https://www.youtube.com/watch?v=dLpmUVDRFbM

Sajal Kumar Adhikary How can we calculate SPI in MATLAB

For SPI calculation in MATLAB, we can get its code through file Exchange method.

We have worked on this issue in these manuscripts that can serve you: Article Systematization of the calculation of the Standardized Preci...

Dear Dr Sandipan Das . See the following useful link: https://library.wmo.int/doc_num.php?explnum_id=7768

Kindly check also the following good link: https://gmao.gsfc.nasa.gov/research/subseasonal/atlas/SPI-html/SPI-description.html

https://agrimetsoft.com/mdm.aspx

https://www.youtube.com/watch?v=dLpmUVDRFbM

Check https://library.wmo.int/doc_num.php?explnum_id=7768

https://www.droughtmanagement.info/standardized-precipitation-index-spi/

Also check https://www.mdpi.com/2073-4433/12/5/603/pdf

https://journals.ametsoc.org/view/journals/apme/53/10/jamc-d-14-0032.1.xml

Check on this website

http://www.wamis.org/agm/pubs/SPI/WMO_1090_EN.pdf

It is calculated at weekly interval. But dry spell between first moisture to current determine the drought.