ACTIVIDAD ECONÓMICA

4.4.1 Fire severity

The Fire Danger Index (FFDI) offers the foremost assessment of potential rate of spread and fire intensity in Australia. It originates from the studies of rates of fire spread utilising a mixture of wind speed, temperature, relative humidity and a drought index. The FFDI ranges from 0 to 100 but can be categorised beyond that limit and values >100 are conceivable during catastrophic weather conditions as seen with the 2009 Victorian fires recording a value greater than 150 (Enright and Fontaine, 2014). Figure 4.2 illustrates the Australian fire seasons with the South West and South East of the country recoding the highest risk to fire events.

Figure 4.2: Australia’s fire seasons highlighting summer and autumn extreme periods in Southern Australia

McCarthy and Tolhurst (2001) studied over 100 bushfires in south eastern forests for the 1990s period and determined as the fire danger increases, the gains from mitigation and suppression strategies reduces. Weather conditions become more significant than fuel parameters in terms of successful risk reduction operations. While uncontrolled fires differ between regions, resources are often concentrated near urban areas and not in natural forests resulting in reliance towards preventative measure such as fuel load management. The current premise is that response mitigation strategies should be directed to protecting human life and assets but these high-risk environments necessitate improved preventative interventions. The Roleystone and Margaret River fires of 2011 have raised uncertainties about the effectiveness of fire mitigation strategies in the southern areas of Western Australia, and highlight this complex relationship between fire, people and the environment (Enright and Fontaine, 2014).

4.4.2 Climate change

Australia is currently experiencing consequences of climate change. Since 1910 Australia has warmed 0.9◦C, greater than the international average of 0.7◦C for the equivalent period. The bulk of this warming has occurred after 1950, with each decade being warmer than the former; the amount of record-breaking hot days has also risen every decade since the 1950s (Head, Adams, McGregor, and Toole, 2014). This increased warmth has altered climate zones for 10.5–29.5◦S south by over 100km along the west coast of Australia. The southwest of Western Australia has also experienced a steady regression in rainfall since the mid-1970s with a 15% decrease in seasonal rainfall. This has resulted in a 60% decline in river flows (Enright and Fontaine, 2014; Head et. al., 2014).

Historically climate trends have been warming, with rainfall increases in northern areas and rainfall decreasing in southern areas. For the forty-year period to 2000, 30% of years were warmer and drier than the previous overall average resulting in the mean fire rate of spread being 66% higher in the December warm-dry years (Matthews, Sullivan, Watson, and Williams, 2012). Forecasted climate changes will have major impacts on Australia’s agriculture, flora and fauna. In southern areas life threatening weather events such as bushfires are likely to increase in intensity and frequency, mostly clustered in summer (Head et. al., 2014). Many people believe that the prospect of preventing climate change entirely has lapsed and increases in the intensity and frequency of climate related events will create new demands and vulnerabilities (Enright and Fontaine, 2014; Head et. al., 2014)

Current climate change predictions for southern Australia include even higher temperatures with reduced rainfall periods resulting in longer dry spells. This is likely to increase the fire risk in areas that are already susceptible to high-intensity bushfires (Hollis et. al., 2011; Keelty, 2011; Drollette, 2005).

Future climate change influences will intensify many of the current trends as it is expected that by 2020 Australia’s climate is will dry further by 10% and 32% by 2050 with significant increases occurring in the southern summer fire season (Enright and Fontaine, 2014; Matthews et. al., 2012). Fire behaviour is controlled by topography, fuel and weather. Of these, fuel and weather are both vulnerable to climate change (Matthews et. al., 2012). The increased occurrence of fire signifies shorter fire intervals and is likely to have major impacts on the age-distribution, composition and structure of forests (Enright and Fontaine, 2014; Williams, Karoly, and Tapper, 2001).

Society is confronted with the challenge of increased risk of uncontrolled fires due to increased fire conducive weather, and asset development in fire prone areas (Enright and Fontaine, 2014; Tonmoy et. al., 2014). There will be more high risk fire days and the moisture content on those days will be lower, with corresponding adverse implications for fire behaviour (Matthews et. al., 2012).

The overall effects on fuel load are uncertain, a warmer and drier climate in southern Australia could lead to reduced overall plant growth and slower rates of litter accumulation (Matthews et al., 2012). Increasing atmospheric CO2 improves

plants water use efficiency which may lead to increased fuel loads due to reduced organic breakdown as a result of a drier climate (Enright and Fontaine, 2014).

Climate change is anticipated to produce modifications in both the extent and composition of vegetation profiles. Fuel load patterns are likely to remain similar to current levels, so that weather will increasingly become the significant factor influencing fire behaviour (Enright and Fontaine, 2014). A reduced winter period associated with lower fuel moisture levels and greater number of fire days will result in an escalation of the rate of spread thus having an adverse impact on fire behaviour (Matthews et. al., 2012).

4.4.3 Prevention measures

Prescribed burning is premised on the theory that fuel age and accumulation rate is important in deciding the fire danger. Fuel loads normally grow with the time since the previous fire, increasing quickly in the first few years until reaching equilibrium where gains from litter production are counterbalanced by losses through decomposition. Because of this, the effectiveness of prescribed burns in

relation to bushfire control decreases as the time since last fire increases (Enright and Fontaine, 2014)

There are a numerous restrictions placed on the areas that can be managed by prescribed burns. These include the planning and endorsement procedures, weather conditions permitting burn activity, potential smoke pollution, and level of resourcing. Weather conditions are important as prescribed burns cannot commence under elevated fire risk weather conditions due to the risk of fire escaping, so the number of burning days available may be low relative to the required area that needs to be burnt (Enright and Fontaine, 2014).

In the forested areas of south west Australia, DPAW plans to burn around approximately 8% or 200 000 Ha of the jarrah (Eucalyptus marginata) forests annually to keep fine litter fuel load below 8 t Ha−1. Increasing the required burn areas to achieve specified management objectives may not be. Recurrent fire intervals of less than 5 years in forests in the south west of Australia are likely to lead to biodiversity losses and vegetation structure alterations (Enright and Fontaine, 2014).

Climate change is predicted to increase the number of catastrophic fire days per year resulting in higher fire intensities compounding the perceived necessity for further prescribed burn activities with shorter intervals. Fire intervals of less than 10 years are liable to cause vegetation losses, especially after drought years. With increased burning, the understorey of the forest is substituted by shrubs and grasses so that fine-fuel accumulation rates are likely to increase rapidly increasing the risk of high-intensity fires that could occur every 2 to 4 years (Enright and Fontaine, 2014).

Chapter 5:

Methodology

This chapter outlines the methodology of the study of ground leaf litter and ash generated from the fire. It includes study design, the area under study, approval requirements and the study methodology.