Enter the annual precipitation and potential evapotranspiration into the calculator to determine the Aridity Index. This calculator can also evaluate any of the variables given the others are known.

Aridity Index Formula

The following formula is used to calculate the Aridity Index.

AI = P / PET


  • AI is the Aridity Index
  • P is the annual precipitation (mm)
  • PET is the potential evapotranspiration (mm)

To calculate the Aridity Index, divide the annual precipitation by the potential evapotranspiration. The result is the Aridity Index, which is a measure of the dryness of the climate. A lower Aridity Index indicates a drier climate, while a higher Aridity Index indicates a wetter climate.

What is an Aridity Index?

An Aridity Index is a numerical indicator used to measure the degree of dryness of the climate at a specific location. It is calculated by dividing the annual precipitation by the potential evapotranspiration (the amount of water that could be evaporated and transpired if there was sufficient water available). A higher aridity index indicates a drier climate. This index is useful in studying climate change, drought conditions, and water resource management.

How to Calculate Aridity Index?

The following steps outline how to calculate the Aridity Index.

  1. First, determine the annual precipitation (P) in millimeters (mm).
  2. Next, determine the potential evapotranspiration (PET) in millimeters (mm).
  3. Next, gather the formula from above: AI = P / PET.
  4. Finally, calculate the Aridity Index.
  5. After inserting the values for P and PET and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Annual precipitation (P) = 500 mm

Potential evapotranspiration (PET) = 300 mm