The world has warmed by 1.9 degrees Fahrenheit since 1880, with the five warmest years on record occurring in the last five years. During these years, the wildfire season also lengthened in several parts of the world. In some places like California, fire has become a nearly year-round risk. Reports have shown that 2018 was California's worst wildfire season on record. In 2019, wildfires also burned 2.5 million acres in Alaska in an extreme fire season driven by high temperatures, leading to massive fires in Siberia.
For the past two decades, NASA satellites have observed fires worldwide and the resulting smoke emissions and burned areas. The researchers found that lighting strikes generated by warmer temperatures are the main natural cause of fires. Human-ignited fires are also a major contributor to the increasing number of wildfires. It was reported that as many as 90% of wildland fires in the US are caused by people. Some fires result from campfires left unattended, the burning of debris, downed power lines, negligently discarded cigarettes and intentional acts of arson.
"Our ability to track fires in a concerted way over the last 20 years with satellite data has captured large-scale trends, such as increased fire activity, consistent with a warming climate in places like the western U.S., Canada and other parts of Northern Hemisphere forests where fuels are abundant. Where warming and drying climate has increased the risk of fires, we’ve seen an increase in burning," Doug Morton, chief of the Biospheric Sciences Laboratory at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said.
According to the Union of Concerned Scientists, a nonprofit science advocacy organization, the total number of acres burned by wildfires and the average acres burned per fire in the US has been increasing in recent decades. Reports show that wildfires burned more than twice as much land per year from 2000 to 2018 compared to 1985 to 1999.
The Role of Weather in Wildfires
Weather plays a major role in the birth, growth, and death of a wildfire. Nick Nauslar of NOAA’s Storm Prediction Center explained the close relationship between weather and wildfire. According to NOAA, an American scientific agency, weather can ignite and/or help spread the fire. This includes stronger winds; low, relative humidity; unstable atmospheric conditions; and thunderstorms. All of these fall under the umbrella of fire weather.
Out of all the three weather factors that can affect wildfires such as temperature, wind, and moisture, the researchers found out that wind has the biggest impact on a wildfire's behavior and is the most unpredictable factor. Warmer temperatures, on the other hand, allow for fuels to ignite and burn faster, adding to the rate at which a wildfire spreads. Experts also discovered that wind does not only affect how the fire develops but fires themselves can develop wind patterns.
Dr. Terry Clark, a senior scientist at the National Center for Atmospheric Research, explained that when the fire creates its own weather patterns, they can feedback into how the fire spreads. At the same time, wildfires can have the potential to create their own pattern. According to AccuWeather, an online site that has local and international weather forecasts, this makes wildfires widely unpredictable and dangerous for firefighters working to control the flames.
Longer, More Dangerous Wildfire Seasons
The frequency or severity of fire-favorable weather conditions is fueled by climate change. A recent study conducted by Richard Betts at the UK Met Office in Exeter and his colleagues discovered that fire weather seasons have lengthened globally between 1979 and 2013. These seasons generally involve hot temperatures, low humidity, low rainfall in the preceding days and weeks, and windy conditions. They reviewed 57 peer-reviewed studies about the link between climate change and wildlife risk.
According to New Scientist, a weekly English-language magazine that covers all aspects of science and technology, the findings of the study suggest that the weather conditions that led to the Australian wildfires will become more common in the future. These more extreme conditions and longer fire seasons are results of climate change instead of fluctuations due to natural variation. Corinne Le Quéré at the University of East Anglia, UK, said that current conditions in Australia will continue to occur when natural large-scale fluctuations combine with a warming climate. “The fact that there is a natural explanation by no means lessens the strong and negative impact that climate change is having,” she said.
With the increasing global temperatures, the likelihood of longer, more dangerous wildfire seasons also increases. Hotter air leaves the trees, shrubs, and rolling grasslands of the countries dry and primed to burn. Unfortunately, Daniel Swain, a climate scientist at the University of California, Los Angeles, explained that the effect increases exponentially with every degree of warming. This can explain the worsening wildfires in California.
Researchers found out that autumn days with weather conditions conducive to extreme fires have doubled in frequency since the early 1980s in California with rainfall during the wildfire season dropping by about 30%. Also, the average temperature has risen by over 2 degrees Fahrenheit over the same timeframe. The highest increases were shown in late summer and early autumn. These factors work together to create very dry plant material in forests and grasslands.
According to Phys.org, an internet news portal that provides the latest news on science, these are what have been feeding the large and fast-spreading wildfires seen across the state in recent years. The impacts of these factors have been seen over the past few years: California’s single deadliest wildfire, the two largest wildfires, and the two most destructive wildfires all occurred during 2017 and 2018, which killed more than 150 people and caused more than $50 billion in damage.
"Many factors influence wildfire risk, but this study shows that long-term warming, coupled with decreasing autumn precipitation, is already increasing the odds of the kinds of extreme fire weather conditions that have proved so destructive in both northern and southern California in recent years," study senior author Noah Diffenbaugh, the Kara J Foundation professor at Stanford's School of Earth, Energy & Environmental Sciences, said.
While scientists are still working on understanding exactly how rain, snow, and winds will change, the warming and drying patterns that cause these wildfires are clear. “It just gets harder to predict. We used to have a much more reliable rainy season and fire season, and a lot of variables are just shifting at the moment,” Faith Kearns, a scientist at the University of California Institute for Water Resources in Oakland, said.