Reevaluating the Haines Index: A Case Study of Major Wildfires

Wildfires pose a serious risk to life, property, the economy, and the environment both at the point of the fire and in the broader region. Not all wildfires are inherently bad for the environment, with small, naturally occurring wildfires helping some ecosystems flourish. However, the large, erratic, often human-caused fires are difficult to contain and extinguish, leading to more adverse impacts, such as increased risk for firefighters. Hot, dry weather, which promotes wildfire ignition and growth, is likely to become increasingly frequent and intense in fire prone areas due to climate change. It is for this reason that fire forecasting needs to become more reliable and accurate. A reevaluation of the Haines Index will help improve fire weather forecasting, especially in fire-prone areas.

The Haines Index (HI) is a commonly used index within the western United States. Select National Weather Service Forecasting offices and fire management teams use the index in briefings and forecasts. It uses lower atmospheric stability and relative humidity to calculate a score between 2-6 that indicates whether a wildfire will become large and quick-moving. Both relative humidity and atmospheric stability are given a number between 1-3 based on their expected conditions, with lower numbers indicating less favorable conditions. Although atmospheric stability and relative humidity are important factors in determining fire potential, only using these terms limits the HI as critical factors that influence fire ignition and behavior, such as wind and fuel moisture, are left out. Some of the most dangerous fires are wind-driven, and the HI’s exclusion of wind could lead to less accurate forecasts, placing first responders and the general public in greater danger. Another problem with the HI is its inaccuracy in determining fire danger in lower elevations. It is for this reason that the index is only used in the western U.S.

To address these issues, we modified the HI to create a new Fire Weather Index (FWI) that includes wind and fuel moisture and evaluated it using a set of five historical wildfires from different locations throughout the United States: the Marshall Fire (Colorado), Smokehouse Fire(Texas), High Park Fire (Colorado), Great Smoky Mountain/Gatlinburg Wildfire (Tennessee) and the 1988 Yellowstone Fire (Wyoming). The five cases were chosen based on the individual fire's growth and severity. The five historical cases are being evaluated according to live-time weather data from both ground observations and meteorological conditions. A comparison of the new FWI to the HI is then used to demonstrate how improvements can help first responders, weather forecasters and the general public.