Computing the Low-Elevation Variant of the Haines Index for Fire Weather Forecasts

Abstract

The Haines index is used in wildfire forecasting and monitoring to evaluate the potential contributions of atmospheric stability and humidity to the behavior of plume-dominated wildfires. The index has three variants ("low," "mid," and "high") that accommodate differences in surface elevation. As originally formulated, the low variant is calculated from temperature observations at the 950-and 850-hPa levels and humidity observations at 850 hPa. In the early 1990s the National Weather Service implemented a new mandatory level for radiosonde observations at 925 hPa. Following this change, measurements at 950 hPa became less frequent. An informal survey of several forecast offices found no formalized adjustment to the calculation of the low Haines index to take into account the nonavailability of 950-hPa measurements. Some sources continue to use 950-hPa temperature, usually interpolated from 925-hPa and surface temperatures, to calculate the low Haines index. Others directly substitute the 925-hPa temperature for the originally specified 950-hPa value. This study employs soundings from the central United States when both 950-and 925-hPa levels were available to investigate the impact of different calculation approaches on the resulting values of the low variant of the Haines index. Results show that direct substitution of 925-hPa temperature for the 950-hPa temperature can dramatically underestimate the potential wildfire severity compared with the original formulation of the Haines index. On the other hand, a low-elevation variant of the Haines index calculated from the interpolated 950-hPa temperature is usually in close agreement with the original formulation of the index.

Satellite contributions to the quantitative characterization of biomass burning for climate modeling

“…However, it is recognized that meteorological factors are also important for the formation and evolution of smoke plumes, beginning with temperature and humidity conditions in the source regions, typically covered under "fire weather" (e.g. Haines, 1988;Potter et al, 2008) and continuing with downwind horizontal advection, vertical mixing, hydration, and precipitation that govern the transport and ultimate deposition of smoke particles.…”

Climatology of the stability and humidity terms in the Haines Index to improve the estimate of forest fire risk in the Western Mediterranean Basin (Valencia region, Spain)

“…TPi and TdPi are the air temperature and the dew point temperature at pressure level Pi, thus both terms A and B are expressed in temperature units. (Haines, 1988;Choi et al, 2006;Potter et al, 2008). …”

“…Depending on the surface elevation above sea level (h) of the region of interest, there are three possible atmospheric layers used for computing the HI, and they provide what are known as the low (h < 1000 feet, lower than 305 m), mid (1000 < h < 3000 feet, or 305 and 914 m, respectively) and high (h >3000 feet, higher than 914 m) elevation HI variants (Table 1; Haines, 1988;Choi et al, 2006;Potter et al, 2008). The low elevation variant was originally developed for the P1 = 950 hPa pressure level; however, the fact that this atmospheric level is not included in numerous atmospheric profile databases led Potter et al (2008) to suggest using P1 = 925 hPa as the standard pressure level.…”

“…The low elevation variant was originally developed for the P1 = 950 hPa pressure level; however, the fact that this atmospheric level is not included in numerous atmospheric profile databases led Potter et al (2008) to suggest using P1 = 925 hPa as the standard pressure level. Table 1 shows the values used for this level (Choi et al, 2006).…”

Verification of National Weather Service spot forecasts using atmospheric sounding observations

“…The HI qualitatively assesses dry, unstable air present in the lower-to mid-troposphere, which can increase wildfire behavior (Haines 1988;Werth et al 2011). Daily fire weather forecasts utilize the HI for determining fire potential, especially for plume-dominated wildfires (Haines 1988;Werth and Ochoa 1993;Potter et al 2008;Werth et al 2011 …”