Precipitation-Based Agricultural Drought Indices

1. Decile Index (DI)

   • Formula: DI = (P / P₁₀) × 100

2. Hutchinson Drought Severity Index (HDSI)

   • Formula: HDSI = ((P - P_avg) / P_avg) × 100

3. Percent of Normal Index (PNI)

   • Formula: PNI = (P / P_norm) × 100

4. Z-Score Index (ZSI)

   • Formula: ZSI = (P - μ) / σ

5. China-Z Index (CZI)

   • Formula: CZI = (P - μ) / σ

6. Modified China-Z Index (MCZI)

   • Formula: MCZI = (6.0 / cs) × ((cs / 2.0) × zsi + 1.0)^(1/3) - (6.0 / cs) + (cs / 6.0)
   • Where cs is the cube of the standardized index.

7. Rainfall Anomaly Index (RAI)

   • Formula: RAI = (P - P_avg) / P_avg

8. Effective Drought Index (EDI)

   • Formula: EDI = (P - PET) / PET

9. Standardized Precipitation Index (SPI)

   • Formula: SPI = (P - μ) / σ