BLAZE A TRAIL I C Jack Roper Modeling fire spread Is wildfire suppression leading to the accumulation of fuel loads and increasing the risk of catastrophic fires? A new modeling system has been developed to investigate this theory n 2020 the state of California saw five of its seven largest wildfires since reliable records began in 1932. A total of 9,917 fires burned 1,780,000ha, or 4.4% of California’s total land area, versus just 105,218ha burned in 2019. Yet prior to 1800, at least 1,821,085ha, and sometimes up to 4,856,227ha, burned in the region now known as California every year, according to UC Berkeley researchers. “We know that fires happened frequently in western North America,” says Susan Prichard, research scientist at the University of Washington College of Forest Resources. “It wasn’t caused just by lightning but also by indigenous cultural burning. For the past century a grand experiment has removed fires from the landscape, allowing fuels to grow and creating a tinderbox.” Prichard believes decades of fire suppression have led to enormous fires recently ravaging the US. For wildfires, mature forests represent combustible fuel. Letting them burn limits fuel build-up and creates resilient landscapes. Putting them out means that when fires do come, they are far larger and less controllable. Reburn is a modeling tool that illustrates this principle. UNDERSTANDING SPOT-FIRE SPREAD ontaining a wildfire can depend on understanding the spread of spot-fires ignited by embers transported downwind by plumes of hot, turbulent air shaped by forest canopies. As Californian wildfires raged in 2018, Stanford PhD researcher Hayoon Chung realized that her study of ocean currents flowing over seagrass could help to understand this process. “We saw some physics from our work on aquatic systems that could translate to the wildfire field,” says Chung. “We modified our experiments in water to reflect parameters of interest in wildfire systems.” Experiments conducted in a 9m water-flume used wooden dowels in repeat patterns to represent forest canopies. As water flowed over them, a hot water jet directed upward through the dowels simulated fire plumes interacting with the canopy. Finally, microplastic rods and spheres representing embers were injected and their downstream dispersion observed. “In fluid dynamics we can model air flow around an airplane by putting it in water,” explains Chung’s colleague, Prof. Jeff Koseff. “We can model flows in water using air. We simply adjust the terms of force equations to compensate for the 8 • www.meteorologicaltechnologyinternational.com • January 2024