Effects of climate on the size of wildfires in the Eucalyptus camaldulensis forests and the dry lands of the Riverina Bioregion, Australia

Abstract

Wildfire affects ecosystem processes, threatens human lives and causes economic loss. In forested wetlands of inland Australia, a better understanding of fire regime pattern is required given the dense population of fire-sensitive species such as Eucalyptus camaldulensis (river red gum). This study aims to investigate wildfire characteristics and the effects and relative contributions of ambient weather and antecedent rainfall on fire size in forested wetlands and the surrounding dry lands of the Riverina bioregion, New South Wales, Australia. Fires burned entirely in forested wetlands (FEW), fires burned partly in forested wetlands (FPW) and fires that did not burn in forested wetlands (FNW), are progressively incorporated into statistical analyses, in order to explore the change of effects and contributions of factors as the fuel type changes from litter/grass to shrub/grass.Forested wetlands and dry lands experience summer and spring-summer fire regime, respectively. Higher cumulative rainfall conditions of the 6th, 13-14th and 17-18th months before fire drive a larger size of FEW, while a number of factors representing the cumulative rainfall after the 18th month before fire positively affect fire size when FPW and FNW are being modelled. A larger fire extent is also driven by severer ambient weather conditions. Forest Fire Danger Index (FFDI) is more powerful in explaining the size of FEW, while the daily temperature becomes more effective when FPW and FNW are gradually incorporated, which supports the use of respective factors as indicators of fire danger in the two diverse ecosystems.Antecedent rainfall factors are more powerful than ambient weather in explaining the size of FEW, while they become less important when the surrounding lands are incorporated. After a high level of rainfall and under similar ambient weather conditions, priority of fire risk management may be given to forested wetlands since fire size is more sensitive to biomass accumulation in forested wetlands than in the adjacent dry lands.