High-Fidelity Experimental Simulations of Atmospheric Flow Near Low-Intensity Fires in a Wildland-Urban Interface

Abstract

With increased urbanization, fires in the wildland urban interface (WUI) have become a severe problem worldwide. The unique features of WUI may influence the atmospheric flows in the vicinity of fire. This study utilizes the parallelized large eddy simulation model (PALM) system for fire-atmosphere simulations of Bottle Lake Forest, Christchurch, New Zealand. Over 3,000 residential buildings are situated around the 7 ${km}^2$ forest, with many homes only 50 m away from the forest edge. We conducted high-fidelity fire-atmosphere simulations with the finest grid spacing of 4 m. Wildland forest (WF) and flat terrain simulations were conducted to provide a reference for comparison with WUI simulations. Fire-weather conditions for the 2022/2023 New Zealand fire season were selected based on the Fire Weather Index (FWI). Data from previous fire field campaigns were obtained to represent a low-intensity fire heat forcing. The results reveal a pulsing behavior in downwind heat transport when the forest canopy is included. Furthermore, the presence of the WUI is associated with extended downwind fire heat transport compared to WF and flat terrain scenarios. This study is the first to simulate atmospheric flows near fires in a WUI setting with such high fidelity. The findings highlight the critical role of WUI features in shaping fire-atmosphere dynamics, though further research is required to disentangle the contributions of individual WUI components to these effects.