Evaluating the performance of WRF in simulating winds and surface meteorology during a Southern California wildfire event

Abstract

The intensity and frequency of wildfires in California (CA) have increased in recent years, causing significant damage to human health and property. In October 2007, a number of small fire events, collectively referred to as the Witch Creek Fire or Witch Fire started in Southern CA and intensified under strong Santa Ana winds. As a test of current mesoscale modeling capabilities, we use the Weather Research and Forecasting (WRF) model to simulate the 2007 wildfire event in terms of meteorological conditions. The main objectives of the present study are to investigate the impact of horizontal grid resolution and planetary boundary layer (PBL) scheme on the model simulation of meteorological conditions associated with a Mega fire. We evaluate the predictive capability of the WRF model to simulate key meteorological and fire-weather forecast parameters such as wind, moisture, and temperature. Results of this study suggest that more accurate predictions of temperature and wind speed relevant for better prediction of wildfire spread can be achieved by downscaling regional numerical weather prediction products to 1 km resolution. Furthermore, accurate prediction of near-surface conditions depends on the choice of the planetary boundary layer parameterization. The MYNN parameterization yields more accurate prediction as compared to the YSU parameterization. WRF simulations at 1 km resolution result in better predictions of temperature and wind speed than relative humidity during the 2007 Witch Fire. In summary, the MYNN PBL parameterization scheme with finer grid resolution simulations improves the prediction of near-surface meteorological conditions during a wildfire event.

Impact of Momentum Perturbation on Convective Boundary Layer Turbulence

“…In boundary-coupled simulations using inflow data that does not contain resolved turbulence at the time and space scales of the LES discretization (e.g., from a mesoscale simulation), the development of resolved-scale turbulence generally requires a long fetch. Therefore, a large LES domain is needed (Mazzaro et al, 2017(Mazzaro et al, , 2019Mirocha et al, 2014;Muñoz-Esparza, Kosović, García-Sánchez, & van Beeck, 2014;Muñoz-Esparza, Kosović, Mirocha, & van Beeck, 2014;Tabor & Baba-Ahmadi, 2010;Zajaczkowski et al, 2011) to capture the development of turbulence at fine scales, increasing computational cost (Connolly et al, 2021;Giani et al, 2022;Kumar et al, 2024;Mazzaro et al, 2017Mazzaro et al, , 2019Mirocha et al, 2010Mirocha et al, , 2014Muñoz-Esparza, Kosović, Mirocha, & van Beeck, 2014). Incorporating adequate representation of turbulence within the model is also advantageous in understanding the role of fire-induced turbulence in wildfire behavior particularly in the wildland-urban interface (dos Santos & Yaghoobian, 2023;Kumar, 2022;Kumar et al, 2022).…”