SPI

VHI

IDI

Drought Classification

>−0.5

>40

6

Normal

−0.5 a −0.8

30 a 40

5

Abnormally Dry

−0.8 a −1.3

20 a 30

4

Moderate Drought

−1.3 a −1.6

12 a 20

3

Severe Drought

−1.6 a −2.0

6 a 12

2

Extreme Drought

<−2.0

<6

1

Exceptional Drought