Enter the average rainfall, evaporation rate, and number of days into the calculator to determine the drought factor. This calculator helps in assessing the severity of drought conditions over a period of time.

Drought Factor Formula

The following formula is used to calculate the drought factor:

DF = (E * D) - R


  • DF is the drought factor
  • E is the evaporation rate (inches per day)
  • D is the number of days
  • R is the average rainfall (inches)

To calculate the drought factor, multiply the evaporation rate by the number of days and then subtract the average rainfall.

What is a Drought Factor?

A drought factor is a numerical value that represents the severity of drought conditions in a specific area over a certain period of time. It takes into account the average rainfall and the rate of evaporation to help determine the water deficit. A higher drought factor indicates more severe drought conditions, which can impact agriculture, water supply, and the environment.

How to Calculate Drought Factor?

The following steps outline how to calculate the Drought Factor:

  1. First, determine the evaporation rate (E) in inches per day.
  2. Next, determine the number of days (D) over which to measure the drought factor.
  3. Next, determine the average rainfall (R) in inches over the same period.
  4. Use the formula DF = (E * D) – R to calculate the Drought Factor (DF).
  5. 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.

Evaporation rate (E) = 0.2 inches per day

Number of days (D) = 30 days

Average rainfall (R) = 1 inch