Regionalization and Spatiotemporal Variation of Drought in China Based on Standardized Precipitation Evapotranspiration Index (1961–2013)

Table 1

Categorization of dryness grade by the SPEI.

SPEI	Categories	Frequency (%)
2.0 ≤ SPEI	Extreme wetness	2.2
1.5 ≤ SPEI < 2.0	Severe wetness	4.4
1.0 ≤ SPEI < 1.5	Moderate wetness	9.2
0.5 ≤ SPEI < 1.0	Slight wetness	15.0
−0.5 < SPEI < 0.5	Normal	38.4
−1.0 < SPEI ≤ −0.5	Slight dryness	15.0
−1.5 < SPEI ≤ −1.0	Moderate dryness	9.2
−2.0 < SPEI ≤ −1.5	Severe dryness	4.4
SPEI ≤ −2.0	Extreme dryness	2.2