Wildfires spread quickly, consuming dry vegetation and other fuels, and inflaming the air to create smoke that can cover large areas. These fires are a threat to millions of acres of natural land and human communities.
Although wildfires can be a serious threat, they also help rejuvenate ecosystems and keep them in balance. They kill insects and diseases that harm trees, as well as clear away scrub and underbrush so that sunlight can reach the ground.
Seasonal Patterns
Various weather conditions influence wildfires and can cause them to erupt at different times of the year. Seasonal weather cycles can result in a convergence of conditions conducive to varying levels of fire occurrence and fire behavior throughout the year (Balice et al 2005). However, this convergence of conditions does not always occur during each season. Therefore, to better understand the relationships between climate and fires, we analyzed the relationship between weather variables and wildfires during specific time periods in the year, referred to as subseasons.
The frequency of fires and fire occurrence varies over a wide range of locations in the US. This variability is influenced by a number of factors including the amount of fuel available to burn, the weather conditions during the fire season, and fire management techniques.
For example, increased fire occurrence over the western United States can be associated with increases in spring snowmelt timing. These climatic changes can lead to an increase in the number of fire danger days (FWI) and the size of these fires.
Furthermore, these increases are correlated with decreases in winter snowpack and rising temperatures. In this study, we examined how the influence of these climatic changes on observed fire activity increases varied over the United States over the last few decades.
We found that the mean US fire weather season length was significantly correlated with variations in annual burned area reported by the National Interagency Fire Center over the full time series from 1979 to 2013 and also from 1992 to 2013, when the quality of the fire occurrence data was highest. This result suggests that longer fire weather seasons are a significant contributor to the increased annual burned area in the western United States over the past few decades.
In the Southwest United States, seasonal fire occurrence is closely linked to dry periods in the spring and fall with greater amounts of precipitation during the summer monsoon period (Allen 2002). This period typically has cooler temperatures and shorter day lengths than those experienced in the spring and fall and therefore does not support a high level of wildfire activity.
Fuels
Wildfires are fueled by a variety of vegetation, which includes grasses, shrubs, trees, and dead leaves. As plants burn, they release carbon dioxide, a gas that helps fires spread. Fuels also contain water, which makes them flammable. The amount of water in a fuel source is important to wildfires because it affects how hot the fire burns and how quickly it can spread.
A number of factors affect the moisture content of fuels, including precipitation, humidity levels, and the type of soil in which the fuel was grown. For example, dead pine needles return a moisture level of around 6%, while living sagebrush can hold up to three times its weight in water.
Fuels also contain oxygen, which allows them to burn at high temperatures and create a yellow flame with white smoke. When fuels lack enough oxygen, they can burn at a lower temperature and show red or orange flames with dark smoke.
Changing climate patterns and human activities have altered the landscape in many places, making it more susceptible to wildfires. However, the frequency of these fires varies widely from one region to the next (Keane et al. 2001).
While wildfires are driven by the weather, the fuels that make up a landscape play a significant role in how they spread and burn. Managing these fuels can reduce the severity of wildfires and help restore and maintain ecosystems.
Mapping the amount of fuel in a landscape is important for predicting fire risk and determining where to focus suppression efforts. Fuel maps can be created by measuring the amount of vegetation in an area and then simulating the growth and mortality of vegetation over time. Vegetation models can then be used to estimate fuel loads and predict changes in fire behavior under different management scenarios and future climate conditions.
These vegetation models have also been used to evaluate the impact of fuel management practices on fire risk. Studies have shown that reducing total fuel loads by removing small and large fuels can reduce wildfire severity and damage.
Despite these efforts, fuels still play a crucial role in the frequency and intensity of wildfires. Understanding how fuels vary in an area and their potential to ignite or spread wildfires requires long-term forestry and fire science research. Increasing the number of long-term forestry and fire science studies will improve our understanding of changes in fuel loads and their effects on fire behavior.
Ignition Sources
In wildfires, ignition sources can come from many different places. Some of the most common ignition sources are natural, such as lightning and lava. Others are human-generated, such as careless smoking and fireworks misuse.
Unlike lightning and lava, human-generated fires are more frequent in the United States and can occur anywhere in the country. These are usually small fires that start in residential or recreational areas and can spread quickly to large acreages.
The number and occurrence of these wildfires are often correlated to local climate conditions (e.g., temperature and rainfall), but this relationship is not perfect. In the southeast, for example, total summer wildfire burn area is correlated to total annual precipitation only in some ecoregions and not others. In the west, however, total annual precipitation is correlated to both human and lightning-ignited wildfires in all ecoregions.
These correlations may indicate that meteorology has an influence on human- and lightning-ignited wildfires, but they are not perfect. Correlations are stronger for lightning-ignited wildfires in Mediterranean California and the Everglades than human-ignited wildfires.
This is because both types of wildfires react differently to atmospheric moisture levels. For example, wildfires started by humans begin earlier in the year and go later than lightning-ignited wildfires.
Also, fires ignite more readily in dry conditions than in wetter environments. This is a function of the fuels themselves, including how well they saturate in water and how quickly they dry out.
Some fuels can self-heat and ignite spontaneously under certain environmental conditions, such as decomposing piles of hay, grains, feeds, manure, sawdust, wood chip piles and piled peat moss. This is called spontaneous combustion.
In the southeastern United States, human ignitions account for 73% of all wildfires and are a more dominant cause of fire activity than lightning-ignited wildfires. Although these are a significant proportion of the wildfires in the southeast, their impact is smaller than in the west where they represent only 30% of the total wildfires.
In the southeastern United States, most human ignitions occur in residential and recreational areas. These can be from careless smoking (especially near interstate highways) or fireworks misuse. Children, particularly those close to home and away from adult supervision, are especially prone to starting fires as they often have a strong desire to play or explore.
Suppression
Suppression methods, the use of water and other chemicals to wet, smother or chemically quench burning fuels, are used to control fires. This includes direct attack by firefighters and aircraft, as well as indirect attack by the creation of control lines that contain no combustible material.
Suppressive tactics are often based on the time of day, particularly when air resources are available to support firefighting operations. Fire intensity is often reduced by cooler temperatures, higher fuel moisture and higher relative humidity. However, personnel may encounter hazards associated with working at night or during reduced visibility.
As climate change continues to exacerbate the frequency of wildfires, the need for new and innovative suppression techniques is becoming increasingly important. These innovations help firefighting crews detect and contain fires more quickly, thereby reducing their impact on human safety, infrastructure and natural resources.
One of the most popular and effective suppression techniques is hot spotting, wherein firefighters focus their efforts on particularly active areas within a fire that pose a threat or are spreading at a rapid rate. Another suppression technique that is becoming more common is aerial attack, wherein helicopters or planes transport water from an exposed source and drop it on the main fire to suppress it.
While this approach is more common in arid climates, the use of these tools can be helpful in other conditions as well. In fact, it’s become an integral part of the firefighting toolkit for both urban and wildland fires across the nation, thanks to new innovations in fire retardants and aircraft technology.
In some cases, hot spotting and aerial attack can be performed simultaneously to reduce the spread of a fire. In other instances, these tactics are used in conjunction with other suppression methods.
Many of these approaches are being adopted by foresters on the ground as a way to address the increasing frequency and severity of wildfires in many Western states, which are now more widespread and severe due to pervasive droughts, earlier/faster snowmelt, and extended growing seasons. It’s a shift in fire policy that forestry officials hope will ultimately help protect the forests they love from future fires.
Comments
Post a Comment