Dynamical linkages between planetary boundary layer schemes and wildfire spread processes: a case study using WRF-Fire version 4.6

Abstract

Wildfires can significantly enhance surface sensible heat and modify the state of the near-surface atmosphere, becoming key factors in triggering turbulence and restructuring the boundary layer. This study uses high-resolution simulations with WRF-Fire, combined with hourly observational data from six meteorological stations (five national and one emergency stations) during the Jinyun Mountain wildfire in Chongqing, China, to systematically evaluate the performance of five planetary boundary layer (PBL) schemes (MYJ, MYNN2, MYNN3, BouLac, UW) in simulating temperature, wind speed, and turbulence intensity. Results show that all schemes can reproduce the diurnal trends of temperature and wind speed but exhibit significant differences in amplitude response and simulation errors. The MYNN3 scheme captures the spatiotemporal variations of turbulence intensity and wind speed at different heights more accurately, thereby better representing the 2 m temperature and 10 m wind speed response and reduces the model's cold bias in high-temperature simulations. The BouLac and MYNN2 schemes also show some response to thermal disturbances at certain sites but perform poorly under strong perturbations and exhibit large fluctuations. The MYJ and UW schemes show overall weaker turbulence and fail to capture local circulation variations effectively. Turbulent energy budget analysis of MYNN3 indicates a buoyancy-dominated turbulence generation mechanism, with vertical transport promoting upper-level disturbances. This reveals MYNN3's greater sensitivity to wildfire thermal perturbations and more complete feedback processes, providing a scientific basis for selecting PBL schemes in mountainous wildfire simulations.