In this study, a threshold level of −1 (negative one) was utilized to identify moderate, severe, as well as extreme drought events in accordance with the computed values of SPI, RDI, and SPEI. This was done in accordance with McKee et al. (1993) drought classes, which are shown in Table 1.
Table 1
DS category classification (Mckee et al. 1993; Tsakiris et al. 2007)
SPI,  , or SPEI values | Category of drought |
|---|---|
| Above 0 | No drought |
| 0.0 to −0.99 | Near normal |
| −1.0 to −1.49 | Moderate drought |
| −1.5 to −1.99 | Severe drought |
| −2.0 and less | Extreme drought |
| SPI, , or SPEI values | Category of drought |
|---|---|
| Above 0 | No drought |
| 0.0 to −0.99 | Near normal |
| −1.0 to −1.49 | Moderate drought |
| −1.5 to −1.99 | Severe drought |
| −2.0 and less | Extreme drought |