Modeling Fire-Atmosphere Feedbacks: Insights from the 2019/2020 Australian Wildfires

Wildfire emissions are a significant environmental concern, especially as climate change is expected to increase the frequency and intensity of extreme wildfires. Numerical weather and chemical transport models often struggle to reliably capture the injection height of wildfire plumes, a key parameter for transport that determines the impact on air quality and climate.

This study uses the ICON-ART numerical model to analyze fire-atmosphere feedbacks and their impact on the aerosol plume. The Australian New Year’s wildfire event of 2019/2020, a period of extreme wildfires and pyro-convection, is chosen as the case study. The simulations are performed with a grid spacing of 6.6 km. At this resolution, convection cannot be resolved, so a plume rise model is employed to parameterize the injection height. However, the resolution is sufficiently fine to account for the impact of the fire on meteorological variables.

Our simulations reveal that fire-induced moisture release leads to increased cloud formation under near-saturation conditions, but the overall impact on plume development is small. In contrast, fire-induced heat release significantly increases the mass-weighted height from the start, driven by sensible heat release, increased injection height, and enhanced convective cloud formation.

Comparison with observations shows that accounting for the heat release by the fire enables the simulation of the observed plume heights. These implementations have the strongest effect on the first simulation day, when the fires are most intense, and are negligible on the last simulation day. For fires with lower intensity, the plume rise model performs well without additional implementations.