The climates of Arizona and New Mexico were analyzed from the standpoint of forest and range fire behavior. Climatological elements of temperature and humidity were used to define the mean equilibrium moisture content during the season of high fire danger. Phenological stages of the lesser herbaceous vegetation were taken as integrators of available moisture, and were used to evaluate the moisture content of the fine fuel complex, which influences fire behavior. Climatological boundaries were primarily defined by marked transition in the equilibrium moisture content field. The time space domain of the fine fuel moisture complex was used as a secondary delineator of boundaries. These applied climatological techniques are now operationally used by fire control and weather agencies in the western United States.
CONCEPTS OF FIRE CLIMATE
Ever since foresters began kicking the forest litter and breaking conifer needles, they have recognized that forest flammability varies in both time and space. The variation is primarily the result of the natural variability of climatological features such as net radiation, winds, precipitation, humidity, and temperature. This variability has influenced the location of fire-danger stations. Attempts are made to place them so they measure conditions "representative" of a surrounding area. Recognition of forest flammability variation also shows up in schemes to extrapolate flammability conditions beyond the area immediately surrounding a measuring station (Barrows 1951).
An objective method of delineating or defining areas that experience similar climatic conditions from the standpoint of potential fire behavior is needed in order to apply meteorology and climatology to wildfire control. We will call these areas fire-climate areas.
In 1941, Hayes (1941) ) investigated the influence of elevation and aspect on fire danger This was a significant step in quantifying the variations in the climate associated with fire danger. He recognized and described three elevation zones with different degrees of fire danger. He attributed these zones to the diurnal influences associated with elevation and aspect.
* Central headquarters at Fort Collins, in cooperation with Colorado State University.