资源环境科技发展态势分析平台

Wildfires are extreme events associated with weather, climate, and environment and have been increasing globally in frequency, burn season length, and burned area. It is of great interest to understand the impacts of wildfires on severe convective storms through releasing heat and aerosols into the atmosphere. We have developed a model capability that can account for the impact of sensible heat fluxes from wildfires on thermodynamics and is computationally efficient. The pyrocumulonimbus clouds associated with the Texas Mallard Fire on 11-12 May 2018 are well simulated by accounting for both heat and aerosols emitted from the wildfire. Both heat and aerosol effects increase low-level temperatures and midlevel buoyancy and enhance convective intensity. Intensified convection along with more supercooled liquid condensate due to stronger vertical transport results in larger hailstones and enhanced lightning. The effects of heat flux on the convective extremes are more significant than those of aerosol emissions.

Plain Language Summary The length of wildfire burning season and burned area have been increasing globally. Besides being a globally important source of aerosol particles that could impact clouds, precipitation, and radiation, wildfire activity heats the environment dramatically and can significantly perturb the environmental thermodynamics. However, this impact on environmental thermodynamics and the subsequent convection generated is poorly represented in models. We have developed and evaluated a model capability that accounts for the impact of heat flux from wildfires and is computationally efficient. We have used the new model to explore a pyrocumulonimbus event that occurred in Texas and Oklahoma on 11-12 May 2018 triggered by the Mallard Fire. The simulation accounting for effects of both heat flux and aerosol emissions from the wildfire predicts radar reflectivity, precipitation, hailstone size, and lightning reasonably well based on comparisons with observations. Both the heat flux and aerosol emissions from the wildfire increase low-level temperatures and midlevel thermal buoyancy significantly, causing stronger upward motion that lifts more supercooled water to higher levels. The increase in available supercooled water for hail growth and invigorated updrafts leads to larger hail size and enhanced lightning. The effect of heat flux on storm intensity is considerably more significant than that of aerosol emissions.