Enter the dew point depression at 850 hPa and the temperature at 850 hPa into the calculator to determine the Haines Index. This calculator can also evaluate any of the variables given the others are known.

## Haines Index Formula

The following formula is used to calculate the Haines Index.

HI = 2 * (TD - 850) + 4 * (850 - T850)

Variables:

- HI is the Haines Index
- TD is the dew point depression at 850 hPa (°C)
- 850 is the constant representing the pressure level (hPa)
- T850 is the temperature at 850 hPa (°C)

To calculate the Haines Index, subtract 850 from the dew point depression at 850 hPa and multiply the result by 2. Then subtract the temperature at 850 hPa from 850 and multiply the result by 4. Add the two results together to get the Haines Index.

## What is a Haines Index?

The Haines Index is a numerical weather prediction tool used to estimate the potential for wildfire growth by measuring the stability and dryness of the air over a fire. It combines the stability of the lower atmosphere and the moisture content of the lower third of the atmosphere. The index ranges from 2 to 6, with 2 indicating a low potential for large fire growth and 6 indicating a high potential.

## How to Calculate Haines Index?

The following steps outline how to calculate the Haines Index.

- First, determine the dew point depression at 850 hPa (TD) in °C.
- Next, determine the constant representing the pressure level (850) in hPa.
- Next, determine the temperature at 850 hPa (T850) in °C.
- Next, substitute the values into the formula: HI = 2 * (TD – 850) + 4 * (850 – T850).
- Finally, calculate the Haines 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.

dew point depression at 850 hPa (TD) = 10°C

constant representing the pressure level (850) = 850 hPa

temperature at 850 hPa (T850) = 20°C