A pyrocumulonimbus (pyroCb) formed over a wildfire near Saumos in Gironde, France on 24 July 2026. The blaze began on 22 July and had burned over 420 sq km by 27 July 2026, prompting mass evacuations.
Definition
- Pyrocumulonimbus (pyroCb): A fire‑generated cumulonimbus produced when intense surface heat drives strong convective updrafts that carry smoke, ash and moisture into the upper troposphere.
Formation and Dynamics
- Updrafts and condensation: Sustained buoyant plumes lift aerosols and water vapour, enabling convective development and anvil formation.
- Pyrogenic winds: Latent‑heat release and descent of cooled air create erratic, often violent local winds that can change fire direction and rate of spread.
- Lightning generation: Electrification within the cloud produces lightning capable of igniting new fires downwind.
Atmospheric and Climatic Effects
- Stratospheric injection: Vigorous pyroCbs can inject smoke and aerosols into the lower stratosphere, affecting regional radiative forcing and long‑range air quality.
- Cloud microphysics: Combustion particles act as cloud condensation nuclei, altering cloud albedo and precipitation efficiency.
Occurrence and Recent Event
- Regional frequency: PyroCbs are most documented in Australia and North America; France had few official records before July 2026.
- Saumos event (July 2026): Fire ignition 22 July; pyroCb observed 24 July; >420 sq km burned by 27 July with widespread evacuations.
IASPOINT Booster Facts
- Terminology: “pyroCb” is the standard abbreviation in meteorology and fire science.
- Detection: Satellites identify pyroCbs via thermal anomalies, overshooting tops and enhanced smoke signatures in infrared bands.
- Related term: “Weather whiplash” denotes rapid swings from wet to dry conditions that elevate fire risk.