Table 1 The classification of SPEI and SSI.

From: Spatiotemporal heterogeneity in meteorological and hydrological drought patterns and propagations influenced by climatic variability, LULC change, and human regulations

Drought grade

SPEI

SSI

No drought

\(SPEI > - 0.5\)

\(SSI > - 0.5\)

Abnormally dry

\(- 1.0 < SPEI \le - 0.5\)

\(- 1.0 < SSI \le - 0.5\)

Moderate drought

\(- 1.5 < SPEI \le - 1.0\)

\(- 1.5 < SSI \le - 1.0\)

Severe drought

\(- 2.0 < SPEI \le - 1.5\)

\(- 2.0 < SSI \le - 1.5\)

Extreme drought

\(SPEI \le - 2.0\)

\(SSI \le - 2.0\)

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