Fire-atmosphere dynamics at a rural-urban interface using turbulence-resolving meteorological simulations

Human settlements in many regions have suffered great damage due to the escalating impacts of wildfires in recent decades. Most human activities have taken place over urban areas and/or Rural-Urban Interfaces (RUI). These areas have their unique vegetative and built fuels and structures, microclimates, and local wind flow dynamics. Despite the significant impacts of wildfires in RUI, only a small number of studies have been done to investigate fire-atmosphere dynamics and wildfire risk at RUI. The parallelized large eddy simulation model (PALM) system 6.0 was used to conduct simulations for a real RUI at Bottle Lake Forest, Christchurch, New Zealand. The simulations contain over 3000 residential buildings spreading around a large pine forest with an area of over 7 km². Fine-scale simulations (Δx = 9 m and Δz = 2 m) were run for the complex rural-urban environment by using initial conditions obtained from larger-scale weather simulations using the Weather Research and Forecasting (WRF) model. A novel experimental-based method allowing for realisation of forest fire heat forcing was developed and implemented into PALM. Heat sources to simulate a forest fire were prescribed at two separate locations for the assessment of the impact of fire locations on wildfire risk on the RUI. In addition, the simulations were performed with two weather scenarios for daytime and night-time conditions, respectively. We aim to investigate the sensitivity of fire-atmosphere dynamic behaviour to different fire ignition locations and weather conditions. Our work specifically focuses on the resulting development of wind gusts and implications for potential firebrand transport paths within the surrounding urban canopy.