There has been a rash of severe wildfires this year, in Europe, the US and elsewhere. A new study, using data on 23 wildfires in America’s western states, shows how such fires grow and spread by creating their own weather. The study, by researchers at San José State University, gathered the wildfire data using Doppler lidar, a form of laser-based radar.
The researchers mounted the lidar equipment on a pickup truck to get close to each blaze. This device fired pulses of light into smoke plumes rising above the fires, and measured the velocity and direction of air currents as the plumes developed.
The results were published this month in the Journal of Applied Meteorology and Climatology, and they confirmed two effects which researchers had only suspected would occur.
One finding was that a bigger fire created a more powerful column of rising hot air. The rising air carried burning embers, and the bigger the fire the greater the risk was of further “spot fires” breaking out downwind many miles away from the original blaze.
The researchers also measured turbulent eddies – whirling patches of intense wind along the edges of fires where the updraught breaks into sections about 100 metres across. These turbulent eddies draw fresh oxygen into the burning zone and fan the flames. They can even produce firenadoes, flaming mini-tornadoes which spread fire rapidly.
Both effects contribute to the spread of wildfires. The bigger the fire to start with the more it is likely to grow. So giant wildfires, of the sort that appear to be increasingly common, could get still larger.
