Forest Fires and Local Weather

Forest fires occur in almost every continent of the world, especially in those regions characterized by a hot and dry climate. A forest fire can be caused by natural phenomena, such as lightning, volcanic eruptions, or spontaneous combustion; however, a forest fire can also be caused by human intervention, including cigarette littering, starting camp fires or disposing  glass particles, which could magnify the sun’s rays, among others.  The occurrence of forest fires depends on relatively short term weather events and the ignition factors involved. Atmospheric conditions along with land conditions and a forest structure may influence the spreading and intensity of a fire

Sources of ignition

Forest fires may occur when the elements needed for a fire come into play. A source of ignition is needed to start a fire. This can be anything from a lighted cigarette to a camp fire to intense radiation from the Sun.  When the source of ignition comes in contact with flammable material, a fire can be started. Materials containing less amounts of water, such as leaves, dried plants and grasses are more susceptible to start a fire.  A fire may grow influenced by the direction of the wind, consuming low-level vegetation and reaching tree canopies. High moisture content, such as that found in dense forest may prevent rapid propagation of a fire; however, in less dense areas, the speed of propagation may derive in a wild fire.

Forest fires and local weather

The presence of vegetation at ground level may affect the amount of water that is evaporated into the atmosphere in dry and wet soil regions. Soil moisture content significantly affects ground surface temperature and relative humidity, influencing the formation of clouds, precipitation and wind speeds. Daytime surface temperatures and relative humidity are affected when the soil moisture is abundant. Vegetation may reduce the amount of evaporation into the atmosphere that is originated by wet soil; however, the burning of vegetation may add its own vapor content into the fire’s local weather. Vegetation also reduces the wind’s speed at surface level by friction.

Pyrocumulus clouds

Very large forest fires may significantly affect air currents, heating air and causing it to rise. Sometimes large forest fires (wildfires) create updrafts, drawing in cooler air to replace heated air, creating vertical temperature and humidity differences. Sometimes, forest fires grow big enough to produce pyrocumulus clouds so intense that these type of clouds create lightning and even rain. Strong winds can reach speeds up to 85 km (53 miles) per hour. A wildfire may advance as winds carry burning materials across rivers and roads. The burning of wood releases water vapor which is released into the atmosphere.

The major causes of fires are attributed to lightning, volcanic eruptions, spontaneous combustions due to solar radiation and sparks from falling rocks; however, global climate change may influence the occurrence of forest fires by making the fire season longer each year. Scientists believe that a rise of one to two degrees in global temperatures in the next 50 years, will affect fire behavior, influencing other factors, including sources of ignition and lightning proportion. Global and regional climate changes could lead to conditions that could enhance the dryness of sources of ignition and the generation of lighting thunderstorms, leading to fuel ignition.

Fires are more common during heat wave or drought seasons and they can start very quickly. A fire can be originated accidentally or caused by arson. scientists usually model the behavior of a fire under varied weather conditions and include a number of climate change scenarios to help better understand forest fires. According to the Natural History Museum, a wildfire can be very destructive and fire-fighters have developed ways to control them however, a fire can play an important role in the lifecycle of animal and plant habitats.