Table 4 Severity levels and value ranges of drought indices.

Standardized Precipitation Anomaly Index (SPAI)¹⁷

SPAI-3

− 1.2 ≤ (SPAI-3)− 1 < − 0.8

− 1.5 ≤ (SPAI-3)− 2 < − 1.2

− 1.9 ≤ (SPAI-3)− 3 < − 1.5

(SPAI-3)− 4 < − 1.9

Vegetation Health Index (VHI)²²

VHI

30 < VHI-1 ≤ 40

20 < VHI-2 ≤ 30

10 < VHI-3 ≤ 20

VHI-4 ≤ 10

Standardized Streamflow Index (SSI)²⁵

SSI-3

− 1 ≤ (SSI-3)− 1 < 0

− 1.5 ≤ (SSI-3)− 2 < − 1

− 2 ≤ (SSI-3)− 3 < − 1.5

(SSI-3)− 4 < − 2

Environmental Drought Index (EDI)³¹

Water Shortage Level (WSL)

WSL < 40%

40% < WSL < 60%

60% < WSL < 80%

WSL ≥ 80%

Drought Duration Level (DDL)

Quarterly (1–3 months)

Semi-annual (4–6 months)

Annual (7–12 months)

> 12 months