Part 4 of the special issue that resulted from the 9th International Conference on Forest Fire Research includes 10 papers on various aspects of wildland fire research. Parts 1, 2 and 3 were published in January, March and June 2023 respectively. All papers in the special issue are published Open Access.

This work analyses the performance of automated fire spread models used in California operationally to predict initial fire spread across landscapes. The models are accurate enough to be used in real-time operations to support preparedness and response actions, although new enhancements are desirable, especially to simulate fires in timber areas.

This study aims to assess handcrew fireline production rates empirically on wildfires in southern Spain. Handcrew fireline production rate increases with direct attack, fuel types with low loads, aerial support and fire containment success. However, it decreases with longer working times and larger fire and crew sizes.

A numerical investigation of liquid (water and retardant) drop from Canadair CL-415 and Dash-8 airtankers is presented. Numerical simulations are reported for the tank discharge as well as for the description of the liquid cloud, characterised by vertical penetration of the liquid, its lateral expansion and the process of atomisation.

A statistical model is used to assess the role played by atmospheric conditions on wildfire activity in the Iberian Peninsula as measured by the Fire Radiative Power (FRP) released by vegetation fires. The largest effects are observed in the regions where climate change is expected to have a pronounced impact.

We compared measurements from three low-cost portable air quality sensors with research-grade instruments for gas and particle emissions in smouldering wildfires. We found that sensors KANE101 and SDS011 can be used in the field after calibration, and improve understanding of using low-cost and portable emission sensors for wildfire measurements.

Traditional burning is used worldwide, but the improper and negligent use of fire has led to association of this practice with rural fire ignitions and negative impacts. A mental model approach was used to systematise motivations, alternative solutions, associated risks, potential impacts and activities leading to a successful burn.

A physics-based study was conducted to quantify firebrand and radiative heat flux on structures in Eucalypt forests. A logarithmic relationship was found between radiative heat flux and firebrand flux. The results assist in improving building construction requirements to mitigate wildfire risk on houses at the wildland–urban interface.

WUI fires are becoming more catastrophic as they are associated with the effects of climate change and human activities. Understanding heat transfer mechanisms from forest fires and how structures ignite is crucial for the definition and implementation of new strategies and techniques, enabling a Performance-Based Design (PBD) approach.

Numerical simulations were used to investigate the impacts of wind, fire intensity and downslope inclination interactions on the heat exposure of an idealised building structure. At higher wind speeds, buildings on steeper downslopes were at higher risk of wildfire impacts. These results are at odds with current Australian building standards.

Air quality deteriorates significantly during wildfire events. The numerical modelling system WRF-APIFLAME-CHIMERE was applied to estimate the impact of the 2021 August wildfires on the air quality of Athens. Calculated values indicate concerning levels of air pollution during the wildfires with potential impacts on health.