Fuel structure controls fire spread in managed urban vegetation patches: field characterisation and FDS simulations from Shanghai

Abstract

Fire risk in urban green spaces is increasing as managed vegetation patches become more exposed to dry conditions, human ignition sources, and dense built environments. Their fuel structure is shaped by planting design and maintenance, yet community-level controls on fire spread remain poorly understood. Using Shanghai as a case study, we combined field fuel characterisation, BehavePlus screening, and Fire Dynamics Simulator (FDS) simulations to examine fire spread in 11 urban plant communities. BehavePlus compared potential surface fire behaviour under controlled wind, slope, and fuel moisture scenarios and identified four high-response communities for FDS analysis. Lower fuel moisture consistently increased surface fire behaviour, while increasing wind speed produced strong increases in maximum rate of spread, fireline intensity, and flame length. Under wind-free conditions, increasing slope produced comparatively smaller responses. FDS simulations showed that spatial configuration influenced fire behaviour differently among communities. Greater horizontal fuel continuity was associated with more connected lateral flame pathways, while vertical fuel arrangement, crown base height, canopy openness, and local airflow were associated with differences in upward fire development. The strongest structural response occurred in a sparse Metasequoia glyptostroboides configuration, indicating that low planting density did not necessarily correspond to lower fire hazard. The findings support fuel-oriented management, including litter and dead fine fuel removal, lower-branch pruning, interruption of continuous shrub and herbaceous belts, and moisture management during dry and windy periods. The study highlights the importance of considering community fuel structure together with species characteristics and planting configuration when assessing urban vegetation fire behaviour.