Impact of Climate Change on Weather Related Fire Risk in the Tasmanian Wilderness World Heritage Area. Climate Change and Bushfire Research Initiative

The Tasmanian Wilderness World Heritage Area Management (TWWHA) has been recognised for its outstanding universal values, with many of these values being dependent on specific fire regimes for their maintenance. For example, the highly fire sensitive palaeoendemics such as king-billy pine, pencil pine, huon pine and deciduous beech may be destroyed by a single fire, while in contrast, buttongrass moorlands and native grasslands may be lost if the period between fires is too long.

Climate Futures for Tasmania data indicates that climate change is highly likely to result in profound changes to the fire regime of the TWWHA, which therefore, has profound implications for values and management of the TWWHA.

The most significant factor which has the potential to impact on the values and fire management of the TWWHA is the projected very large increase in dryness. This increase in dryness is re ected in the increases in the Mount Soil Dryness Index (MSDI), the number of days in a season when the MSDI exceeds the critical threshold of 50 and the number of times in a season when there are greater than 30 days with less than 50 mm of precipitation.

In summer, these enhanced levels of dryness will mean that when bushfires occur (from whatever cause) the potential for the fires to burn into organic soils, rainforest and alpine areas will be greatly increased. In addition, by 2100 conditions typical of summer are projected to be about eight weeks longer. These changes are projected to start occurring in the near-future time period (ie 2010 to 2030) and get progressively worse by 2100.

The window within which planned burning can be reliably conducted will be greatly reduced. This will be due to spring being reduced in length by about two weeks and autumn by about six weeks. In addition, mean wind speeds are projected to significantly increase in spring (but less so in autumn and summer), further restricting the potential for planned burning. This will mean that by 2100 the number of days per season suitable for planned burning in the TWWHA will be reduced by about half.

The occurrence of dry lightning is projected to steadily decrease, however, it is likely that this will be more than offset by the very substantial increases in soil and fuel dryness. In addition, large outbreaks of dry lightning are projected to occur earlier in the season. As a result, the widespread fires ignited by these events are likely to be present in the landscape for more of the season leading to larger fire affected areas.

The increased potential for summer bushfires that result from the enhanced dryness has the potential to reverse the marked reduction in arson, accidental fires, and escaped management burns that have occurred in the TWWHA between the 1970s and 2010s. In doing so, it is possible this increase in fire potential will result in a return to the situation that prevailed over the 100 years prior to the 1970s when catastrophic impacts to fire sensitive paleoendemics occurred. These impacts included the destruction of about 30 to 50 % of king-billy pine, more than 50 % of pencil pine forest, and 10 % of huon pine, along with extensive areas of deciduous beech and organic soils.