With increased urbanisation, fires in the wildland urban interface (WUI) have become a severe problem worldwide. The unique features of WUI may influence fire-atmosphere interactions. This study utilises the parallelized large eddy simulation model (PALM) system for fire-atmosphere simulations of Bottle Lake Forest, Christchurch, New Zealand. Over 3000 residential buildings are situated around the 7 km2 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. In comparison to WUI simulations, flat terrain simulations were carried out as a reference for idealised scenarios. 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 the fire heat forcing. Our results show that the WUI simulation coincides with fire heat transport going further downwind than its flat terrain counterpart. Kelvin-Helmholtz waves were present in both the WUI and flat terrain simulations, generating downdrafts from higher levels to the surface. However, downwind heat transport coincides with a pulsing behavior only in the WUI. In addition to these characteristics, analysis of the ambient atmosphere shows that the WUI plays the main role in modifying fire-atmosphere interactions. This study is the first to simulate fire-atmosphere interactions in WUI with such a high fidelity. Our results provide insights into the impact of WUI on fire-atmosphere dynamics. More work is needed to further understand how each component of WUI can alter fire-atmosphere interactions.

We present novel in-field vegetation fire observations, and the analyses used to process the data, using brightness temperatures recorded by longwave infrared camera and thermal image velocimetry. The brightness temperatures from a wind-driven stubble wheat fire were obtained in video format with a 60 frames per second (fps) acquisition rate. Multi-level sonic anemometers mounted on a 10m in-fire tower were used for in-situ measurements of turbulent velocity and air temperatures, while fuel level air and flame temperatures were collected by an array of thermocouples. The camera’s image pixel resolution was adequate to resolve dynamics and in accordance with the in-fire thermocouple spacing distances. The in-situ and remotely measured flaming zone dynamics were derived using two different methodologies, Thermal Image Velocimetry (TIV) and Image Segmentation (IS). The results highlight spatial and spectral information of coherent turbulent and mean velocity structures. The power spectra decomposition of the thermal image velocimetry showed similar spectral characteristics to the sonic velocity measurements during the fire passage under the tower with a similar inertial subrange slope. This result reveals plausible evidence of interaction between the flaming zone and wind turbulence for a prescribed rapidly moving stubble wheat fire. This research presents a new field measurement methodology for understanding fire-atmospheric interactions between the flaming zone and the immediate overlying atmospheric turbulent boundary layer.