Depending on these factors, a fire can quickly fizzle or turn into a raging blaze that scorches thousands of acres. Fuel can include everything from trees, underbrush and dry grassy fields to homes. The amount of flammable material that surrounds a fire is referred to as the fuel load.
Fuel load is measured by the amount of available fuel per unit area, usually tons per acre. A small fuel load will cause a fire to burn and spread slowly, with a low intensity. If there is a lot of fuel, the fire will burn more intensely, causing it to spread faster. The faster it heats up the material around it, the faster those materials can ignite.
The dryness of the fuel can also affect the behavior of the fire. When the fuel is very dry, it is consumed much faster and creates a fire that is much more difficult to contain. Small fuel materials, also called flashy fuels , such as dry grass , pine needles, dry leaves, twigs and other dead brush, burn faster than large logs or stumps this is why you start a fire with kindling rather than logs. On a chemical level, different fuel materials take longer to ignite than others.
But in a wildfire, where most of the fuel is made of the same sort of material, the main variable in ignition time is the ratio of the fuel's total surface area to its volume. Since a twig's surface area is not much larger than its volume, it ignites quickly.
By comparison, a tree's surface area is much smaller than its volume, so it needs more time to heat up before it ignites. As the fire progresses, it dries out the material just beyond it -- heat and smoke approaching potential fuel causes the fuel's moisture to evaporate.
This makes the fuel easier to ignite when the fire finally reaches it. Fuels that are somewhat spaced out will also dry out faster than fuels that are packed tightly together, because more oxygen is available to the thinned-out fuel. More tightly-packed fuels also retain more moisture, which absorbs the fire's heat. Drought leads to extremely favorable conditions for wildfires, and winds aid a wildfire's progress -- weather can spur the fire to move faster and engulf more land.
It can also make the job of fighting the fire even more difficult. There are three weather ingredients that can affect wildfires:. As mentioned before, temperature affects the sparking of wildfires, because heat is one of the three pillars of the fire triangle. The sticks, trees and underbrush on the ground receive radiant heat from the sun, which heats and dries potential fuels.
Warmer temperatures allow for fuels to ignite and burn faster, adding to the rate at which a wildfire spreads. For this reason, wildfires tend to rage in the afternoon, when temperatures are at their hottest. Wind probably has the biggest impact on a wildfire's behavior. It also the most unpredictable factor. Winds supply the fire with additional oxygen, further dry potential fuel and push the fire across the land at a faster rate.
Terry Clark, senior scientist at the National Center for Atmospheric Research, has developed a computer model that shows how winds move on a small scale. Since , he's been converting that model to include wildfire characteristics, such as fuel and heat exchange between fires and the atmosphere.
Clark's research has found that not only does wind affect how the fire develops, but that fires themselves can develop wind patterns. When the fire creates its own weather patterns, they can feed back into how the fire spreads. A fire needs three things: fuel, oxygen and heat.
Firefighters often talk about the fire triangle when they're trying to put out a blaze. On a hot summer's day when drought conditions peak, something as small as a spark from a train wheel can ignite a raging wildfire. Sometimes, fires occur naturally, ignited by heat from the sun or a lightning strike. However, most wildfires are because of human carelessness such as arson, campfires, discarding lit cigarettes, not burning debris properly, playing with matches or fireworks.
Once it's started, a wildfire can spread due to the wind, being on a slope or because of fuel. So if a fire is going up a mountain it will go very fast. Fuel includes everything from trees, underbrush and dry grassy fields to homes. The more fuel there is, the more violently the fire will burn. Plus if it's really dry - like it has been in most of those countries - the fire it creates is much more difficult to control.
Low rainfall causing a drought, searing hot temperatures and wind all make the perfect recipe for a wildfire. Remember the heat in the fire triangle? Then you can win and suppress it really effectively. There is even a practice guide on preventing wildfires in the UK.
This involves picking less flammable trees, planting them in places where they're less likely to set on fire and harvesting them regularly. Image source, AP. How do wildfires start? Topless and homeless, they spent the night in their van after being evacuated from their homes. Why can they spread so quickly? This video can not be played To play this video you need to enable JavaScript in your browser.
What's the weather got it do with it. Quite a lot actually. Maybe we would have [strong] winds, but it would be too wet to start a fire [in California]," Quinn-Davidson said. But mid-November of was dry enough to perpetuate the most deadly and destructive fire in the Golden State's history.
Though it's been a record-breaking year in California, wildfires are not new. In fact, they are a natural and necessary part of many ecosystems, including California's forests. But the wildfires we see today are different from those natural blazes, burning faster and hotter.
We've never seen that before. The change in our climate, perpetuated by human-made greenhouse gas emissions, extends the window of the annual fire season. But wildfires also burn faster and hotter simply because there is more fuel to burn. For example, the boreal forest in Canada and Alaska has seen an increased number of lighting-ignited wildfires since , likely due to earlier snow melts and fuel drying brought on by global warming, a study in the journal Nature Climate Change found.
0コメント