Hi Alireza,

perhaps also you could find interesting the review of Zargar et al. [2011] on drought indices:

http://www.nrcresearchpress.com/doi/abs/10.1139/a11-013#.W1TUNrgzWCo

Cheers

Yannis

Not sure it answers your question. see chapter 3.3 (and screenshot here in annex)

Article Indicators of the impacts of development on environment: A c...

The Zargar et al. (2011) citation suggested by Yannis and Salehnia et al., (2017):Article Estimation of meteorological drought indices based on AgMERR...

Standardized Precipitation Index (SPI) is one the reference accepted indices of Drought by the world climatic organization for the drought occurrence (Potop et al., 2012; Khosravi et al., 2015)

See http://www.ipcc.ch/pdf/special-reports/srex/SREX-Chap3_FINAL.pdf Box 3-3 page 167 to 169

Recently two new methods namely Modified SPI and JDI for hematological drought detecting have been proposed and their developers claim they don't have drawbacks of simple SPI method.

You can also use the HHSI which is descriped in the following article

Article Development of Climate-Based Index for Hydrologic Hazard Sus...

The application of drought indices is based on a number of factors among them being based on user knowledge, needs, data availability and computer resources available to implement them. Reference can be obtained from A Handbook Drought Indicators and Indices @ http://www.droughtmanagement.info/find/guidelines-tools/handbook-drought-indicators-and-indices/

What matters most is the availability of relevant data and experts needed to undertake the indices as well as software packages. In support of what Dr Ongoma noted, it would be good if someone in need of using the various drought indices should consult the WMO guidelines. Moreover, it is possible to compute each of the index and compare them to identify the robust ones. For example, myself and the coauthors of our manuscripts have used both SPI and SPEI, each to serve the objective intended to achieve. For more information, please find the attached WMO guidelines.

The various indices have been developed and applied to quantify and monitor meteorological drought development, sometimes for specific conditions. These are detailed in the different references including; discrete and cumulative precipitation anomalies, rainfall deciles, Palmer Drought Severity Index (PDSI), Drought Area Index (DAI) and Rainfall Anomaly Index (RAI) (Heim, 2000, 2002; Keyantash and Dracup, 2002; Vincente-Serrano et al., 2011; Dai, 2011). The precipitation anomalies and deciles are simple to compute, but they are especially less informative and can easily show end of a drought period even if the precipitation received is not enough to terminate the water shortage. Even though the PDSI, DAI and RAI are robust, they involve complicated computations and are not versatile. DAI for instance was developed specifically for Indian conditions. In addition to these indices is the Standardized Precipitation Index (SPI) which is based on long-term precipitation data fitted to probability distribution functions (McKee et al., 1993; Guttman, 1998; Komuscu, 1999; Jain et al., 2015; Van

Loon, 2015).

The SPI is recommended because of its accuracy and simplicity (Guttman, 1998; Komuscu, 1999; Jain et al., 2015), and versatility allowing it to also detect the occurrence of wet spells at different time.

I therefore have the opinion that the SPI is the most acceptable.

I am interested in the drought phenomenon. My doctoral thesis was about the effect of drought on wheat and barley production in governorates in Iraq. I also supervised a master thesis on drought indicators and used the SPI index