Haines Index Description


The Haines Index is a simple way to measure the atmosphere's contribution to the growth potential of a wildfire. It was developed by a USDA Forest Service research meteorologist Donald Haines, in 1988. The Haines Index is an index that gives an indication about the potential for a fire "blow-up". A fire "blow-up" would lead to extreme fire behavior. The index uses the environmental lapse rate within a layer of air coupled with its moisture content to determine a Haines Index. The Haines Index combines two atmospheric factors that are known to have an effect on wildfires: Stability and Dryness.

The Haines Index is also dependent on elevation. Three combinations of atmospheric layers were used to construct the Haines Index (Low, Middle and High). For the purposes of our local (SW PA) Fire Weather Forecasts, WSFO CAE will use the middle elevation Haines for the "low-lands" and mid-lands zones, and the high-level Haines for the uppermost Mountainous zones. Primarily in the state of PA. the middle elevation will be the predominate Index used.

current Haines Index

The Haines Index is the sum of a stability term and a moisture term. The sum provides an indication of the potential for the rate of spread (ROS) of a fire on a given day. A Haines Index of 2-3 = a very low ROS, 4 = low ROS, 5=moderate ROS, and 6 = high ROS. The National Weather Service uses the Lower Atmospheric Severity Index (LASI) to quantify the potential for forest fire growth.

Haines based the low-elevation version of his index on temperature observations at 950 millibar (mb) and on temperature and humidity observations at 850 mb. In 1988, measurements were commonly taken at the 950 mb pressure level, even though this level was not a mandatory sounding level (required by NWS rules). The 850 mb level was-and remains-a mandatory level.

In 1991, the NWS introduced a new mandatory level at 925 mb. Measurements at 950 mb became less frequent. While some soundings still include 950 mb data, the majority do not. There has been no coordinated, standard adaptation of the low-elevation Haines Index to account for this change.
  • Stability: Stability is a term used to describe the tendency for vertical air motion in an air mass. A stable atmosphere tends to discourage any vertical air motion while an unstable atmosphere promotes it. A wildfire stands a much better chance of growing large in an unstable air mass because vertical motion encourages the growth of the smoke column. This would increase the chance of spotting and crowning and a very strong smoke column can eventually create its own wind. i.e. become a plume dominated fire.
  • Dryness: The drier the air mass, the drier the fuels are likely to be. Thus, more combustive energy is released and fire spread is enhanced.
Since the Haines Index is intended to be used all over the United States it is adaptable for three elevation regimes: Low Elevation, Middle Elevation and High Elevation.

Low Elevation is for fires occurring at or very near sea level.
Middle Elevation is for fires burning in the 1000-3000 foot elevation range.
High Elevation is intended for fires burning above 3000 feet elevation.

LOW ELEVATION Stability Term (T950-T850)
1....3 deg C or less
2...4 to 7 deg C
3...8 deg C or gtr
Moisture Term (T850-Td850)
1...5 deg C or less
2...6 to 9 deg C
3...10 deg C or gtr
MID ELEVATION Stability Term (T850-T700)
1...5 deg C or less
2...6 to 10 deg C
3...11 deg C or gtr
Moisture Term (T850-Td850)
1...5 deg C or less
2...6 to 12 deg C
3...13 deg C or gtr
HIGH ELEVATION Stability Term (T700-T500)
1..17 deg C or less
2...18 to 21 deg C
3...22 deg C or gtr.
Moisture Term (T700-Td700)
1...14 deg C or less
2...15 to 20 deg C
3...21 deg C or gtr

Fire weather offices regularly calculate the Haines Index. Haines Index data becomes available shortly after weather balloons are released at selected locations across the nation at 5:00 am PDT and 5:00 pm PDT each day during the fire season.
There are some strengths and weakness associated with the Haines Index which will be elaborated on.
  • Advantages:
    • The Haines Index is a quick and easy way to combine two important atmospheric factors into one simple value. If upper atmospheric data is available, the Haines Index is quite easy to compute. The Haines Index can then be calculated for daily operational use or for historical weather research.
    • The Haines Index tends not to "cry wolf" too often. A 1990 study at the Boise Fire Weather Office found that a Haines Index value of 6 occurred on only 6% of the days during the fire season. However, it was on these days that 75% of the season's total acreage was burned! On the other hand, days with a Haines Index of 2, 3, or 4 occurred much more often but only 7% of the total acreage was consumed.
  • Drawbacks:
    • The Haines Index does not take wind into account at all. It is possible to have a low Haines Index value while the wind is creating a very dangerous fire situation.
    • The Haines Index does not take into account fuel moisture. It only measures moisture at the 5000 and 10000 foot levels in the free atmosphere. Moisture at these upper altitudes may not be representative of the relative humidity conditions at the surface where the fuels are.
    • The Haines Index does not account for terrain, fuel continuity, slope or ignition risk. The index quantifies the growth potential only of existing fires.
    • The Haines Index can only be calculated at locations where a radiosonde weather balloon sounding is available. These soundings tend to be about 300 miles apart in the contiguous U.S. If a fire occurs in a region between these locations the meteorologist must estimate what the Haines Index is at the fire location. The estimates tend to be pretty good but terrain effects may modify the local conditions.
  • Availability:
    • The Haines Index is available only twice a day...5am and 5pm during the summer. Atmospheric conditions may change between these reporting times.
  • Predictability:
    • The Haines Index is difficult to predict. Since the index is computed from temperature and humidity values at several levels of the upper atmosphere, precise forecasts of these factors are necessary at each level. New computer modeling technology is allowing meteorologists to attempt such fine scale forecasts but only time will tell whether they are accurate enough to be useful.
Don't let all the drawbacks listed above discourage you! The Haines Index is very useful for evaluating wildfire growth potential. The danger comes with the mentality that this one index "solves the whole problem." It does not! It is only one more tool that partially measures the atmosphere's contribution to fire growth potential. The fire manager must still evaluate the other legs of the fire triangle...fuels, terrain and all aspects of weather.

Interesting Weather Facts
MOON PHASE MISCONCEPTION
"The most common incorrect reason given for the cause of the Moon's phases is that we are seeing the shadow of the Earth on the Moon! But this cannot be correct: When the Moon passes through the shadow of the Earth, we get a lunar eclipse. Anyone who has seen a lunar eclipse, though, might remember that the Moon actually passes through the Earth's shadow only rarely, so that can't be why the Moon has phases. The real reason for the Moon's phases depends on two things: The Moon is round, and the angle it makes with the Earth and Sun changes over its orbit."
- As Quoted From Bad Astronomy