Forty years of micro-weather observations provide insights into variations of in-forest vapor pressure deficit (VPD) within a mixed eucalyptus foothill forest fire regime change

The threat to life and property, and the relationship between fire regimes and biodiversity, are arguably the most significant ongoing challenges facing managers of parks and forests. Fuel moisture is a primary driver of fuel flammability and subsequent fires and varies spatially and temporally across landscapes. Vapour Pressure Deficit (VPD) is a measure of atmospheric dryness that strongly influences dead fuel moisture content. Previous research has established strong links between VPD, burned area, and fire severity at broader spatial and temporal scales. More recent work has found in-forest VPD is generally a stronger predictor of ignition and sustained burning than broader landscape variables. Understanding the spatial-temporal trends and variability of VPD is crucial for understanding future wildfire risk and estimating what (if any) management actions can reduce risk.

This study utilizes a long-term (40 year) dataset of in-forest VPD collected from weather stations established in 1984 in eucalyptus forest in southeastern Australia. Data were analysed to map temporal variations in VPD across different microclimates within the forest. Thresholds from previous research were used to determine availability for ignition and spread. Seasonal analyses were undertaken to examine the potential for wildfires (summer) or prescribed fire (spring and autumn).

The number of potential wildfire days has increased in the summer period over the duration of the study, with an acceleration in the last twenty years.  Prescribed fire opportunities have also increased however these results should be cautiously interpreted as they may also represent an extension of the wildfire season compared to historic conditions. 

Long term micro-climate studies are rare, and these data provided unique insight into the spatial-temporal variations of VPD within a eucalyptus forest in southeastern, Australia. These data support the notion that changes in climate are a much greater driver of fire regime changes, compared to land management decisions.