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Environment: Drought drives overnight burning of wildfires (N&V) *IMAGES*
Drought conditions are likely to increase overnight burning of wildfires in North America, reports a study published in Nature. The results have important implications for the management and prevention of wildfires.
Conventional understanding of the diurnal (day to night) fire cycle has traditionally been that the lower temperatures and higher humidity associated with nighttime can naturally slow the progression and intensity of wildfires. In recent years, studies have reported an increase in the frequency and duration of overnight fires, raising concerns that environmental changes could be enabling wildfires to surpass this natural barrier and burn more powerfully at night. However, the precise reasons for this increase have yet to be identified.
Kaiwei Luo and colleagues examined 23,557 fires that occurred in North America between 2017 and 2020, using a combination of satellite and terrestrial data to analyse the burn cycle of these fires and identify overnight burning events (occasions when fires burned continuously throughout the whole night).
The authors identified 1,095 overnight burning events in 340 individual fires. Most of these events were found in large fires (larger than 1,000 hectares), with 20% of large fires having at least one overnight burning event. These events were commonly early onset (occurring within two days of ignition) and in 67% of cases they were detected on two consecutive nights, suggesting that one night of burning frequently leads to a second. Notably, it was found that the increased availability of extremely dry fuel associated with drought conditions was the most important factor in predicting overnight burning events, overcoming the effects of lower nighttime temperatures and higher humidity.
The presence of drought conditions could then act as a predictor of overnight burning events the following night, facilitating early detection and improved fire management. In addition, the authors observe a rise in extreme-weather conditions that are conducive to overnight burning events in recent decades, emphasizing the importance of understanding the effect of our changing climate and weather on the diurnal cycle of wildfires.
