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

## Drought Index Formula

The following formula is used to calculate the Drought Index.

DI = (P - E) / (P + E)

Variables:

- DI is the Drought Index
- P is the total precipitation received during a specific period (mm)
- E is the total evapotranspiration during the same period (mm)

To calculate the Drought Index, subtract the total evapotranspiration from the total precipitation received during a specific period. Then, add the total precipitation and the total evapotranspiration. Divide the first result by the second result to get the Drought Index.

## What is a Drought Index?

A drought index is a numerical scale used to characterize the severity and impacts of drought conditions over a certain period and area. It integrates various factors such as rainfall, temperature, soil moisture, and evaporation rates to provide a comprehensive understanding of the drought situation. Different drought indices such as the Palmer Drought Severity Index (PDSI), Standardized Precipitation Index (SPI), and the U.S. Drought Monitor are used globally to monitor and manage drought conditions.

## How to Calculate Drought Index?

The following steps outline how to calculate the Drought Index.

- First, determine the total precipitation received during a specific period (P) in millimeters (mm).
- Next, determine the total evapotranspiration during the same period (E) in millimeters (mm).
- Next, gather the formula from above = DI = (P – E) / (P + E).
- Finally, calculate the Drought Index.
- After inserting the variables 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.

total precipitation received during a specific period (P) = 120 mm

total evapotranspiration during the same period (E) = 80 mm