Aridity Index

Q. Which one of the following defines Aridity Index $\left(AI\right)$?

(where AET = Actual Evapotranspiration and PET = Potential Evapotranspiration)

1. $AI=\frac{\text{PET - AET}}{\text{PET}}\times 100$
2. $AI=\frac{\text{PET}}{\text{AET}}\times 100$
3. $AI=\frac{\text{AET}}{\text{PET}}\times 100$
4. $AI=\frac{\text{AET - PET}}{\text{AET}}\times 100$

Q. Palmer index is used for

1. Mateorological drought
2. Hydrological drought
3. Agricultural drought
4. None of the above