Reassessing Traditional Suppression Practices: New Empirical Evidence for WUI Prevention and Preparedness

Recent fire events in the Wildland-Urban Interface (WUI) - such as the Athens wildfire in 2024 -  highlight the urgent need for governments to strengthen preparedeness and resource management. While structural vulnerabilities, evacuation strategies, and population preparedness have received considerable attention, a persistent and insufficiently addressed gap remains: the lack of empirical data on the effectiveness of traditional water-based firefighting methods under realistic conditions. This data gap is particularly acute for Central and Northern European countries, where forest fires are still often contained using water-based approaches solely. Operational guidelines from regions with a long history of fires are rarely adapted to local vegetation, infrastructure, or climatic conditions. As fire regimes intensify and spread to new geographic areas, this reliance on unvalidated assumptions regarding fire suppression risks compromise preventative planning and the resilience of fire-prone areas.

 

This article presents a field-tested methodology for quantifying the effectiveness of water-based fire suppression at field-relevant fire intensities (>1000kW/m). For the first time, it defines an empirical operational window that directly guides the planning of risk mitigation measures in the WUI as well as water reservoir dimensioning. Conventional fire suppression guidelines rely largely on theoretical calculations of critical water depth, derived from simplified energy balance models or expert opinions, and their empirical validation remains limited in medium- and high-intensity fire environments.

 

To address this gap, we developed a field-reproducible experimental protocol that combines: (i) precise characterization of drift-prone water deposition using a controlled grid and cup system, (ii) controlled pre-wetting of natural fuel beds using a bespoke soaker hose as a water distribution system, (iii) measurement of fire intensity at the fire front using calibrated geometric flame models, and (iv) a binary classification of containment outcomes based on containment or burn-through events. Ten experiments, conducted during test and controlled fires in Portugal and Spain, provided a validated dataset establishing a correlation between the applied water depth (0.9 to 3.1 mm) and the extinguishing results of advanced flames with intensities ranging from approximately 2,200 to 5,700 kW/m².

 

These results define the first empirically documented operational window for a ground-based fire suppression system and demonstrate that effective containment can be achieved with water depths significantly lower than those recommended by existing theoretical guidelines. This finding has direct implications for wildfire prevention: it enables more precise resource planning, supports the development of shelter strategies based on realistic extinguishing performance, and provides a quantitative basis for assessing the role of water distribution networks in community-level disaster preparedness. For countries newly exposed to fire risk, this methodology offers an adaptable and transferable framework for adjusting suppression targets, aligning emergency planning with local vegetation and infrastructure, and reducing vulnerability through evidence-based prevention.