Attached please find an comprehensive document on the same by WMO, check out pages 7 -9.

I would recommend SPEI, SPI and scPDSI. You can compute them in R – packages spei (for SPI and SPEI) and pdsi (for scPDSI).

It is a good idea not to rely on a single drought index.

You can find below a very comprehensive review of drought indices used in USA in the 20th century, by Dr RR Heim Jr (2002) (NB: SPEI is newer):

Article A Review of Twentieth-Century Drought Indices Used in the Un...

Well,

the following is the simple one.

Sincerely

Two books

Book Indicators of climate change based on daily data (ICC)

Book Climate change analysis with monthly data (Clic-MD)

Dear Ahmad

When we want to calculate the meteorological drought indices we need to have meteorological data for at least 30 years. for rain-based drought indices we just need precipitation that I invite you to read the following links for calculation all of them:

DOI:10.1007/s40333-017-0070-y

https://agrimetsoft.com/MDM.aspx

https://agrimetsoft.com/RDIT.aspx

If we have other input data beside precipitation such as maximum temperature, we can use other meteorological indices such as KBDI (Keetch Byram Drought Index):

https://agrimetsoft.com/KBDIS.aspx

If you have other data other evapotranspiration (ET) and field capacity (FC) or soil moisture you can calculate PDSI (Palmer Drought Severity Index):

https://agrimetsoft.com/drought%20monitor.aspx

If you have any question for calculating details of each index, let me know. I can clarify the details since I calculate all of them.

Sincerely,

@Nasrin Salehnia

You can calculate SPI, RDI, and many indices based on rainfall data using 'DrinC' software. It is a free and useful tool. Just Google it.

SPI and SPEI are the important indices to indicate meterological drought.

Hi

use the Handbook_of_Drought_Indicators_and_Indices_2016 of World Meteorological Organization

You can use Clic-MD software, https://www.actswithscience.com/e-shop/?lang=en

I have used the Agricultural Reference Index for Drought (ARID)(https://doi.org/10.2134/agronj2011.0286). For agricultural purposes, I prefer to use indices that take into consideration the soil-plant-atmosphere relationship and ARID does it. These is one of the indices listed in the FAO handbook mentioned by Subhash Chavare.

Hi

You can find the formula of 20 indices in this pdf file:

https://www.researchgate.net/publication/377081457_drought_indices_formulaspdf?utm_source=twitter&rgutm_meta1=eHNsLWZVVzU1TDJGcFN3ekM4UVJ0VWY1VG9IbzFzYjVxbEVONXNNQkxDS1VGUll1RUNlT0Nxb2I1K3ZVNzIvZGx5QzRpb1R3OThRUUgydzlJL1BlOU9tK05RPT0%3D