A Holistic Modelling Framework for Assessing Risks of Wildfires Along the Wildland Urban Interface within New Zealand

Wildfire risks are projected to increase in the future due to climate change, coupled with increased exposure along the wildland-urban interface (WUI) due to population growth and growing cities.

This research presents a modelling framework for simulating potential risks posed by wildland fires to urban areas across the WUI via a multi-stage, loosely coupled approach:

Stage 1 - Wildfire: Using Spark, user-defined equations determine fire spread behaviour (Miller et al. 2015). To calculate Rate of Spread (RoS) and Fireline intensities for New Zealand vegetation types, equations from Pearce (2005) are applied. These, along with localised climate data for current and future conditions, create wildfire scenarios. Flame heights and radiant heat flux (RHF) are spatially analysed at each time-step to assess risks to transport networks, critical infrastructure, and buildings near or outside urban areas along the WUI.

Stage 2 – Building-to-building fire: With ignition points at urban boundaries defined, the second stage of the modelling framework uses a physics-based building-to-building fire spread model like that outlined in Himoto (2022) to simulate urban fire propagation over time. This, combined with wildfire model outputs, informs the risk assessment and micro-scale evacuation model.

Stage 3 – Ensemble risk assessment:  Fire exposure from previous stages is used to assess risks to infrastructure and transportation networks. A method, adapted from Butler and Cohen (1998), defines RHF values and maps it to the transport network. This data informs the evacuation model, defining safe zones and low-risk evacuation corridors.

Stage 4 – Evacuation modelling:  Building on work by Evans et al. (2020), the evacuation model integrates hazard outputs with micro-scale transport models to simulate evacuee movement under extreme scenarios. By incorporating movement restrictions and evacuee behaviours, it assesses risks to evacuees navigating the network.

Together, these four stages provide a comprehensive risk assessment of wildfires and key insights for refining evacuation planning strategies.

Acknowledgement

This project has received funding from the European Union's Horizon Europe research and innovation programme under the grant agreement number 101147385. Views and opinions expressed are however those of the authors only and do not necessarily reflect those of the European Union or CINEA. Neither the European Union nor the granting authority can be held responsible for them.

References

Butler, W, B., Cohen, D, J. (1998). Firefighter Safety Zones: A Theoretical Model Based on Radiative Heating International Journal of Wildland Fire 8(2) 73 – 77. https://doi.org/10.1071/WF9980073

Evans, B., Chen, A.S., Djordjevic, S., Webber, J., Gómez, A.G., and Stevens, J. (2020). Investigating the 421 effects of pluvial flooding and climate change on traffic flows in Barcelona and Bristol. Sustainability, 422 12(6), 2330. https://doi.org/10.3390/su12062330

Himoto, K. (2022). Large Outdoor Fire Dynamics – Fire Spread Simulation (pp 333 – 367). 1^st Edition. CRC Press. http://dx.doi.org/10.1201/9781003096689-10

Miller, C., Hilton, J., Sullivan, A., Prakash, M. (2015). SPARK – A Bushfire Spread Prediction Tool. In: Denzer, R., Argent, R.M., Schimak, G., Hřebíček, J. (eds) Environmental Software Systems. Infrastructures, Services and Applications. ISESS 2015. IFIP Advances in Information and Communication Technology, vol 448. Springer, Cham. https://doi.org/10.1007/978-3-319-15994-2_26

Pearce, G. H. (2025). Appendix 3: Sub-contracted Report: Fuel Load and Fire Behaviour Assessments for Vegetation within LCDB2