F2: Fire risk

Introduction

This indicator is assessed using the Fire Danger Index and the Fire Danger Ratings which are derived from the index. It should be noted that the Fire Danger Index and associated Fire Danger Ratings do not necessarily correspond to the incidence of bushfires, they only estimate the potential severity of bushfire occurrence given the predicted weather conditions. For more information see Background: Fire.

Fire severity risk

The ACT’s annual Fire Danger Ratings varied greatly over the 1994–95 to 2022–23 period in response to annual temperature and rainfall conditions (Figure 9). Elevated fire severity risk occurs during periods of drought and hot weather, potentially leading to more severe fires (if they were to occur) and an increased difficulty in fire suppression. There is a much lower severity risk of fire during wetter years (for example, 2010–11 to 2011–12 and 2020–21 to 2022–23).

The ACT’s Fire Danger Index and Fire Danger Rating data also shows that:

• Catastrophic ratings are rare in the ACT with only three days occurring between 1994–95 and 2022-23. However, all of these occurrences are linked to the ACT’s most severe bushfires with catastrophic conditions recorded on the first day of the 2003 bushfires (18 January 2003) and two recorded catastrophic conditions in the weeks leading to the Orroral Valley fire in January 2020.
• Extreme ratings are also rare with only eight days occurring between 1994–95 and 2022–23. Three of these occurrences were in the 2019–20 fire season.
• Days of increased Fire Danger Rating occur most often in January, followed by December and February. Increased fire severity risk conditions also occur frequently in November and March.

There is no apparent long-term increase in the overall number of elevated fire danger days, nor an increase in the number of days in the higher risk categories (very high, severe, extreme and catastrophic Fire Danger Ratings). Despite this, climate change is expected to increase the ACT’s fire severity risk in the future (see Climate change).

There has been an increasing number of consecutive fire seasons with elevated fire severity risk in the ACT. This is particularly evident for the 2012–13 to 2019–20 fire seasons which saw an increased number of days with elevated risk conditions over the entire period (Figure 9). Extended periods of elevated fire severity are likely to increase the chance of a significant bushfire occurring. This was certainly the case for the 2020 bushfires which occurred after eight years of elevated risk conditions.

This increasing duration of elevated fire severity risk is also evident in the ACT’s mean Fire Danger Index anomaly which shows that most years since 2000 had a greater fire severity danger than the long-term average (Figure 10). Prior to 2000, there were generally longer periods of reduced fire severity risk that were punctuated by short durations of high risk. However, increased temperatures and drought have led to longer periods of elevated fire severity conditions (see Climate change). The highest mean Fire Danger Index anomaly between 1950 and 2022 occurred in 2019. This is likely a factor in the severity of the 2020 bushfires.

Fire severity risk 2019–20 to 2022–23

Over the reporting period (2019–20 to 2022–23), the ACT saw highly variable fire severity risk conditions, from the elevated severity risk occurring in 2019–20 which led to the 2020 bushfires, to the greatly reduced risk in the wetter years since 2020 (Figures 9 and 10).

The fire severity risk conditions in 2019–20 were particularly elevated in the month leading up to the Orroral Valley fire and for the first days of the fire (Figure 11). Fire severity risk conditions included two catastrophic and two extreme risk days, seven severe days, ten very high, and nine high risk days. Such conditions significantly increased the severity and spread of the Orroral Valley fire, particularly through increased temperatures and the drying fuel loads.