Characterizing the Role of Moisture and Smoke on the 2021 Santa Coloma de Queralt Pyroconvective Event Using WRF-Fire

Smoke from wildfires or burning biomass directly affects air quality and weather through modulating cloud microphysics and radiation. A simple wildfire emission coupling of black carbon (BC) and organic carbon (OC) with microphysics was implemented using the Weather Research and Forecasting model's fire module. A set of large-eddy simulations inspired by unique surface and upper atmospheric observations from the 2021 Santa Coloma de Queralt Fire (Spain) were conducted to investigate the influence of background conditions and interactions between atmospheric and fire processes such as fire smoke, ambient moisture, and latent heat release on the formation and evolution of pyroconvective clouds. While the microphysical impact of BC and OC emissions on the dynamics of fire behavior is minimal on short time scales (<6 hr), their presence increased the cloud water content and decreased the rain rates in our case study. In our case study, atmospheric moisture played an important role in the formation and development of pyroconvective clouds, which in turn enhanced the surface winds (8%) and fire spread rate (25%). The influence of fuel moisture on the pyroconvective cloud formation is smaller when compared with the atmospheric moisture content. A better representation of cloud processes can improve the mesoscale forecasts, which is important for better fire behavior modeling.Plain Language Summary Pyroconvective clouds are formed directly as a result of wildland fires. They are influential on fire behavior, hard to predict, and impose hazardous conditions on the first responders and people in the area. Various environmental factors, such as atmospheric moisture, fuel moisture, fire intensity, and smoke, impact the formation and evolution of these clouds. Smoke from wildfires or burning biomass affects air quality and weather directly. The impact of smoke on the weather is either through radiative effects or cloud formation. Cloud water condensation can occur on the smoke particles where new cloud drops form. These processes are not currently represented in WRF-Fire, a model simulating weather and wildfire evolution and interactions. We have implemented a simple emission model to represent the effect of smoke on the clouds. We investigated the impact of atmospheric and fuel moisture, as well as the smoke, on the pyroconvective clouds. We rely on unique in situ measurements to design our simulations and interpret the results. The availability of atmospheric moisture is essential for the formation of pyroconvective cloud. When a pyroconvective cloud forms, it creates faster winds, which, in turn cause faster fire propagation.