Severe fire weather

Key messages

  • The Forest Fire Danger Index (FFDI) is used to estimate fire weather risk.
  • Severe fire weather days (FFDI >50) are projected to increase across NSW throughout this century.
  • By the end of the century, severe fire weather days are projected to triple under a high-emissions scenario in some areas.
  • Regions west of the Great Dividing Range are projected to experience the greatest increases.
  • Coastal regions are projected to also see increases, especially under high-emissions scenarios.
  • NARCliM2.0 provides high-resolution climate change projections for NSW and south-east Australia

Context

What is Forest Fire Danger Index (FFDI)

The Forest Fire Danger Index (FFDI) represents an estimate of fire weather risk. FFDI is calculated from temperature, relative humidity and wind speed, as well as an index representing soil dryness.  

Impacts

Severe fire weather (FFDI > 50) is most likely to occur in summer and spring1. Increases in severe fire weather heightens the risk to communities, infrastructure and ecosystems. 

Severe fire weather days, which create the underlying conditions for large-scale bushfires, are expected to become more common in the future, particularly under a high-emissions scenario. Climate change is also expected to reduce the interval between severe fire weather, increase fire intensity and shorten the window for safe fire management activities2. 

For communities on the bushland-urban interface, the increased occurrence of severe fire weather heightens risks to people, homes and infrastructure3.

Key findings

Climate projections

The NSW and Australian Regional Climate Modelling (NARCliM)2.0 projections show that the number of severe fire weather days (FFDI > 50) will increase across NSW throughout the century under a low- (SSP1-2.6) medium- (SSP2-4.5) and high-emissions (SSP3-7.0) scenario (Figure 1 and 2). 

During the baseline periodi, 1990–2009, NSW had on average 9.5 severe fire weather days per year. 

By the middle of the centuryii

map of NSW future projections for fire
Figure 1. Projected change to average annual number of severe fire weather day by 2040-2059 (compared to 1990-2009 baseline period) under a low (left), medium (centre) and high (right) emissions scenario.

The average number of FFDI days is projected to increase by:

  • 3.2 per year under a low-emissions (SSP1-2.6) scenario
  • 3.4 per year under a medium-emissions (SSP2-4.5) scenario
  • 5.3 per year under a high-emissions (SSP3-7.0) scenario

By the end of the centuryiii

Figure 2. Projected change to average annual number of severe fire weather day by 2080-2099 (compared to 1990-2009 baseline period) under a low (left), medium (centre) and high (right) emissions scenario.

The number of FFDI weather days is expected to have an even greater increase by the end of the century under a medium-emissions (SSP2-4.5) scenario and a high-emissions (SSP3-7.0) scenario.

The average number of severe fire weather days is projected to increase by:

  • 3.5 per year under a low-emissions (SSP1-2.6) scenario
  • 7.2 per year under a medium-emissions (SSP2-4.5) scenario and
  • 9.4 per year under a high-emissions (SSP3-7.0) scenario

The projections show that:

  • the number of severe fire weather days is projected to increase during spring and summer. The largest increases are typically expected in summer, although some regions have a greater increase during spring.
  • increases to severe fire weather days will occur across most of NSW, with many regions projected to experience a doubling or even tripling of severe fire weather days by the end of the century under a high-emissions scenario.
Figure 3. Historical and projected change in annual number of severe fire weather days – NSW under a low-, medium- and high-emissions scenario.


 

Geographic impacts – FFDI

While fire plays a key role in the natural cycles of NSW4, increases in the number of FFDI occur in all regions of NSW with the greatest increases occurring in areas west of the Great Dividing Range (Figures 1 and 2). 

Areas such as Bourke in the Far West region are projected to experience 7.6 additional severe fire weather days under a low-emissions scenario, 14.8 additional severe fire weather days under a medium-emissions scenario and 19 additional severe fire weather days under a high-emissions scenario – the number of severe fire weather days is approximately double Bourke’s baseline period average of 18.8 severe fire weather days per year.

Some coastal regions are also projected to experience increases in severe fire weather days under a medium-emissions scenario and a high-emissions scenario, with limited changes expected under a low-emissions scenario. By 2090, Nowra in the Illawarra Shoalhaven region is projected to experience 0.8 additional severe fire weather days per year under a low-emissions scenario, 1.8 additional severe fire weather days under a medium-emissions scenario and 2.1 additional severe fire weather days per year under a high-emissions scenario. During the baseline period, Nowra experienced an average of 2.1 severe fire weather days per year, and a high-emissions scenario could double the number of severe fire weather days per year.

Applications and adaptation

Risk assessment and climate modelling

The FFDI plays an essential role in fire risk assessments by providing a quantifiable, real-time measure of fire danger, which helps in mobilising resources, issuing warnings, and implementing fire bans during periods of high risk. 

It also enables long-term climate and fire risk modelling; as climate change leads to increased temperatures, altered rainfall patterns, and drought conditions, the FFDI has shown an upward trend, indicating rising fire danger over time. FFDI and projections can be used by emergency services and communities to help prepare for bushfire threats, response planning, climate and hazard assessments, and long-term fire risk trends.

In climate risk assessments and modelling, FFDI can be used to project future bushfire risks under various climate scenarios helping identify risk, allocate resources and develop strategies for mitigation and adaptation. 

By understanding the number of days per month or year of severe or greater fire danger rating, emergency services and communities can better prepare for bushfire threats and plan response. It also contributes to the understanding of how ecosystems may need to respond or adapt to changing probable fire conditions in the future. However, it may not be comparable across different bioclimatic zones and regions.

Further reading and information

Technical Description

FFDI is a widely used metric in Australia that estimates the potential severity of bushfires on a given day and location. It was developed by CSIRO scientist A.G. McArthur and is a key component of the country's fire danger rating system. 

Number of days where FFDI is greater than 50 (FFDIgt50)

Description: The Forest Fire Danger Index (FFDI) represents an estimate of fire weather risk. The FFDI is calculated from temperature, relative humidity and wind speed, as well as a number representing fuel dryness. This index is simply the number of fire days with and FFDI rating of 50 or greater. It includes Severe, Extreme and Catastrophic ratings.

Units: Number (days)

Frequency in NARCliM2.0: Monthly and Yearly

References

  1. Bin Wang, Allan C. Spessa, Puyu Feng, Xin Hou, Chao Yue, Jing-Jia Luo, Philippe Ciais, Cathy Waters, Annette Cowie, Rachael H. Nolan, Tadas Nikonovas, Huidong Jin, Henry Walshaw, Jinghua Wei, Xiaowei Guo, De Li Liu, Qiang Yu, Extreme fire weather is the major driver of severe bushfires in southeast Australia, Science Bulletin, 2022, Volume 67, Issue 6, Pages 655-664, https://doi.org/10.1016/j.scib.2021.10.001.
  2. Hennessy, K., B. Fitzharris, B.C. Bates, N. Harvey, S.M. Howden, L. Hughes, J. Salinger and R. Warrick, 2007: Australia and New Zealand. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden and C.E. Hanson, Eds., Cambridge University Press, Cambridge, UK, 507-540.
  3. IPCC 1997, The regional impacts of climate change: an assessment of vulnerability. Cambridge University Press, UK.
  4. N.D. Burrows, Linking fire ecology and fire management in south-west Australian forest landscapes, Forest Ecology and Management, Volume 255, Issue 7, 2008,
    https://doi.org/10.1016/j.foreco.2008.01.009.
Time periods in this document

i. Baseline period: The modelled average for each climate variable from 1990–2009, used for comparison with future projections.

ii. Middle of the century: The projected annual average for severe fire weather days (FFDI >50) for 2040 to 2059. This is compared against a historical model baseline period of 1990 to 2009 (9.5 days). The projections for each time period represent averaged data across all 10 NARCliM climate models.

iii. End of the century: The projected average for severe fire weather days (FFDI >50) for 2080-2099. This is compared against a historical model baseline period of 1990 to 2009 (9.5days) The projections for each time period represent averaged data across all 10 NARCliM climate models. 

NARCliM2.0

New South Wales and Australian Regional Climate Modelling (NARCliM)2.0 provides nation-leading climate model data that spans the range of plausible future changes in climate. It offers:  

  • climate projections to the year 2100, and simulations of the past  
  • 4-km scale projections for south-east Australia, 20-km scale projections for the broader Australasian region
  • projections under low (SSP1–2.6), medium (SSP2–4.5), and high (SSP3–7.0) emissions scenarios to understand how climate risk differs depending on emissions pathways (Shared Socioeconomic Pathways, SSPs). 
NARCliM2.0 Resources (Adapt NSW)

Regional Climate Change Snapshots: The NARCliM2.0 projections are summarised as snapshots to provide accessible climate information that can support NSW communities to understand and plan for the impacts of climate change

Interactive Climate Change Projections Map: Select the region, climate variables and timescale in your area to explore what your region may look like in the future.

Climate Data Portal: The NSW Climate Data Portal variables dictionary provides technical descriptions and applications for each index 

NSW Government, The NARCliM modelling methodology, Adapt NSW

NSW Government, NARCliM data processing, testing and validation, Adapt NSW

Linked Datasets