on-shore sea-breeze, as opposed to dry season wind from inland)?ġ. How might the direction of wind flow influence humidity (e.g.How does humidity vary across Northern Australia and how does it vary seasonally? What might this mean in terms of probability of fires?.Which months typically have the lowest humidity and which the highest?.Now have a look at the graphs which show how relative humidity changes throughout the year in different regions of the Northern Territory, Queensland and Western Australia, and consider the following questions.įor locations of these sites refer to maps on the Geosciences Australia website. The following graph illustrates the relationship between humidity and temperature. Activity: Humidity & temperature How does humidity vary diurnally? In the monsoonal tropics of northern Australia, this means that surface fuels become more flammable as the dry season progresses. For example, in dry conditions, moisture from fuels is transferred to the atmosphere and the fuels become increasingly flammable. Humidity is important because it affects fuel moisture content and therefore its flammability. Humidity varies with temperature – as temperature increases humidity decreases (and vice versa). Expressed as a percentage, it describes the amount of water vapour in the air compared to the amount needed for the air to be saturated (i.e. Relative humidity (RH) is a measure of how much moisture is in the air. Spotting occurs when a fire produces sparks, embers or flaming material (such as loose bark) which are carried by the wind and start a fire ahead of the flaming front (outside the perimeter of the fire). Wind can also influence the likelihood of spotting. They can be problematic as they can carry burning debris outside the fire perimeter, sparking new fires. Notice that a change in wind direction from the NW to SW has caused the flank fire to become the new fire front - much larger and potentially more difficult to control than the original narrow front.įire whirlwinds can form during or after fires, and are created by surface heating and atmospheric instability. The following diagram illustrates the fire that can result from a change in wind direction. Wind is a major controlling factor that determines rate and direction of spread, and shape of fire. The most important weather variables are wind, atmospheric humidity and temperature. Fire weather data is important because it describes the prevailing weather conditions affecting fire behaviour.
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