L-band microwave-retrieved fuel temperature predicts million-hectare-scale destructive wildfires

The 2014 Northwest Territories fires are one of the largest wildfires in history. However, it is difficult to explain what caused such devastating wildfires simply with meteorological conditions and hydrological drought. There is a lack of large-scale Near-Real-Time (NRT) observations that characterize fuel conditions. To fill this research gap, we provide the new earth observations that the meso-scale vegetation heat represented by L-band microwave-retrieved fuel (or canopy) temperature serves as a predictor of fire spread and lightning. We studied two million-ha-scale extreme fire events in the Northwest Territories in 2014 and British Columbia in 2018 to demonstrate that preheated endothermic vegetation condition (canopy temperature>295 K) ahead of flaming is a prerequisite for mega-fires. Canopy temperature is thus proposed as an indicator to modulate convective heating ahead of combustion, and fire spread, which strongly correlated (R2 of 0.8 ∼ 0.9) with pre-fire canopy temperature increments. It is possible to predict large-wildfires with this threshold of canopy temperature. We suggested a mechanism for vegetation under heat stress to trigger ignition and spread large fires. Our findings provide additional evidence that continued warming of the Earth's surface will lead to more severe firestorms and carbon emissions.