I would strongly recommend you the R package SPEI. It employs monthly input values and was used to produce the Global SPEI Database (http://sac.csic.es/spei/database.html). It also includes functions to compute monthly ET0 estimates with various combinations of meteorological parameters. 

Have a look here: https://cran.r-project.org/web/packages/SPEI/index.html

http://sac.csic.es/spei/database.html

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

Hi Sabrija

the SPEI index is not that complicated. You could use a simple excell sheet to do it yourself ....

That is what I did for the SPI.

Either if you have direct evaporation data ready to useor even If you have to calculate the evaporation from primary variables, Excell is still fne anyway.

Best

Gil 

Daniele, I tried the SPIE package in R, as you said it takes monthly data for SPEI, SPI and can compute monthly ETo. Manual for this software is a bit confusing especially for somebody who is not the expert in R.

For the other suggestion, yes sure excel can be used, but as you already know, it takes a lot of time and knowledge to make such excel sheet. I assume that your excel sheet for SPI can be easily used for SPEI by just putting the values of simple water balance Precipitation - ETo (required for SPEI calculation) instead of precipitation data (required for SPI).

Thanks.

I don't know if you have already got the answer of what you wanted, another software that calculates ETo is DrinC calculator, well it does not compute SPEI but RDI which is also water balance, maybe i can be helpful, this is purely developed by Tigkas and others in Greece for people who know nothing about any programming. 

Thanks, I was using software that you mentioned, but as you said it compute only RDI. I spend few days learning software that Daniele Nerini suggested and I can tell you it is a bit confusing in beginning but when you understand it calculations are done in few minutes. 

Dear colleagues, while I was learning to work with the R package SPEI I made an easy step by step manual for it. Attached to this message, hope it helps.

Research HOW TO USE: Package 'SPEI' For BASIC CALCULATIONS

An excutable SPEI file(spei.exe) can be found in http://digital.csic.es/handle/10261/10002.

Actually, the SPEI not only requires monthly rainfall, but also at least monthly temperature for its calculation. The aim of calculation is a transformation high skewed of accumulated climate water balance anomalies ( accumulated rainfall minus potential evapotranspiration) to a standard normal variable. This work needs a proper distribution function. In the work of (Vicente-Serrano, S.M. et al., 2010), the author suggested log-Logistic distribution function.

I developed a small code intergrating with SPEI package in R software in order to test the goodness of fit of the fitting function (log-Logistic) to the target time series. You can find by the below link. My purpose is to get people understanding the way of SPEI calculation and examining the capacity of SPEI on a specific area. 

http://rpubs.com/hungle510/202764

Gil Mahe, can you kindly provide the formula to calculate SPEI in excel

Hi

My team and I developed a complete software for calculating 18 drought indices including SPEI.

This software is actually a comprehensive and user-friendly software that you can easily calculate every indices (18 indices) that you want. The input format file of data can be in different format, namely nc, txt, xls, xlsx,...

It is very useful.

Please make a contact with the following website that to inform you when it upload in the site:

www.agrimetsoft.com

Also you can send an email to:

[email protected]

Hope it will be nice,

Regards,

Nasrin Salehnia

www.agrimetsoft.com

Hi, Nasrin SalehniaI am searching SPEI in youe website, but unable to find. Please help me in this regrds.

Thank in Advance

Would it be possible to use SPEI for shorter scale like daily or weekly?

Hi all seniors, i am masters student is asian institute of technology and now i am doing research thesis on Drought for that i am using SPEI package in R Studio, but i am confused for plot and results copying. Can you assist me with your kind suggestions in this regard please ?

Faisal

Email address

[email protected]

Yes. Try SPEI in R software

You can use R with SPEI package

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

If anyone want to calculate SPEI for spatial or NetCDF data, do let me know.

I have gridded data and I want to calculate SPEI index on each grid point. Can anyone help me out here, if possible?

Md Saquib Saharwardi I am wanting to calculate SPEI for spatial data. I am looking to create a map of SPEI accross multiple grid points for a single point in time. Could you help me with this?

Hi Teya,

Please clarify your query.

You are asking about multiple grid point orsingle point dataaet.?

Hi Dear All

About Teya's question.

She wants to calculate SPEI for a region with multiple gridded points. In my opinion, the best way is to use a gridded data set for the aim region. In this regard, you can use CRU data and use the input data of SPEI (such as precipitation,

temperature, radiation, etc. (to calculate ET), or you can use the ET data of CRU), or also other gridded dataset sources.

Then you extract the input data of SPEI then after you can calculate this index. But according to my experience, when my students wanted to extract their gridded data of the selected source (such as CRU, TRMM, AgMERRA), they made mistakes to produce an excel file from nc format.

Be careful; when you want to calculate a perfect outcome from a drought index, the primary step is collecting right and precise input data of that drought index. If you extract your data wrongly, you obviously can't get the right and exact results. So, your final results and conclusions wouldn't be acceptable.

If you want to calculate drought indices for a region, I invite you to see the bellow link:

https://bit.ly/2GoFit6

If you have another question or clarifications, let me know.

Best Regards,

Nasrin

I have gridded rainfall data. now i want to extract monthly rainfall data ( in mm) to calculate SPEI. how can I get it?

Your gridded data are monthly time step?

If yes, first identify the exact coordinates of the grid points which correspond to the area for which you want to calculate rainfall, then write a program to read the grid and store the values for the grid points selected.

Once extracted and stored, you can use these data as any other time series

1. Use R software for both tasks extraction and SPEI computing.

2. or use GIS software (I used QGIS) and use point data extraction tool to get RF data. Then use R software for calculating SPEI.

Hi Ritu! if you can get the source code of first program, we can make it run on windows. also for the second tool in R, we can make changes to suit your data resolution.

Cheers.

Rajveer

Thank you all for your answers, they have been helpful

Please I want to calculated TDVI, I have spatial data from MODIS

There is user-friendly software for this aim. The name is DMAP here: https://agrimetsoft.com/drought%20monitoring%20and%20prediction