Coupled Fire-Cloud Simulations Reveal Attenuation and Self-Intensification Mechanisms of Pyrocumulonimbus Clouds

Pyrocumulonimbus (pyroCb) firestorms, which inject climate-altering aerosols into the stratosphere, represent a growing and unpredictable hazard in an era of increasing wildfire activity. The complex fire-atmosphere feedbacks that govern their behavior, however, are poorly understood, limiting forecasting capabilities. Here we use high-fidelity, fully coupled simulations to dissect the competing mechanisms controlling pyroCb evolution. We show that fuel moisture primarily acts as an energy sink that attenuates fire intensity and suppresses pyroCb development, rather than serving as a significant moisture source for the cloud itself. Conversely, we identify a potent positive feedback loop, the Self-Amplifying Fire-induced Recirculation (SAFIR) mechanism, where precipitation-induced downdrafts intensify the parent fire. Our simulations reveal that the prevalence of either attenuation or SAFIR-driven intensification is dictated by ambient conditions, particularly wind speed. These findings provide a new mechanistic framework for understanding pyroCb behavior, offering a critical step toward improved prediction of these extreme events.