Abstract

Climate dynamics at diurnal, seasonal and inter-annual scales shape global fire activity, although difficulties of assembling reliable fire and meteorological data with sufficient spatio-temporal resolution have frustrated quantification of this variability. Using Australia as a case study, we combine data from 4760 meteorological stations with 12 years of satellite-derived active fire detections to determine day and night time fire activity, fire season start and end dates, and inter-annual variability, across 61 objectively defined climate regions in three climate zones (monsoon tropics, arid and temperate). We show that geographic patterns of landscape burning (onset and duration) are related to fire weather, resulting in a latitudinal gradient from the monsoon tropics in winter, through the arid zone in all seasons except winter, and then to the temperate zone in summer and autumn. Peak fire activity precedes maximum lightning activity by several months in all regions, signalling the importance of human ignitions in shaping fire seasons. We determined median daily McArthur forest fire danger index (FFDI50) for days and nights when fires were detected: FFDI50 varied substantially between climate zones, reflecting effects of fire management in the temperate zone, fuel limitation in the arid zone and abundance of flammable grasses in the monsoon tropical zone. We found correlations between the proportion of days when FFDI exceeds FFDI50 and the Southern Oscillation index across the arid zone during spring and summer, and Indian Ocean dipole mode index across south-eastern Australia during summer. Our study demonstrates that Australia has a long fire weather season with high inter-annual variability relative to all other continents, making it difficult to detect long term trends. It also provides a way of establishing robust baselines to track changes to fire seasons, and supports a previous conceptual model highlighting multi-temporal scale effects of climate in shaping continental-scale pyrogeography.

Highlights

  • Landscape fires play a crucial role in the Earth system, influencing vegetation distribution and structure, the carbon cycle and climate (Bowman et al 2009)

  • Patterns in fire activity In all 61 climate regions, there are clearly identifiable fire seasons, given that there is a substantial part of a given year when there is little fire activity, a period when fires burn only in the day-time and a shorter period when fires burn at night as well as during the day

  • Fire seasons vary across a latitudinal gradient, from spring in the monsoon tropics to late summer and autumn in the temperate zone

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Summary

Introduction

Landscape fires play a crucial role in the Earth system, influencing vegetation distribution and structure, the carbon cycle and climate (Bowman et al 2009). A global study which combined modelled lightning projections under enhanced emissions scenarios with fire ignitions modelled through a land surface vegetation model (Krause et al 2014) found a 21.3% increase in cloud-to-ground lightning strikes over the coming century. This is predicted to increase the area burnt by lightning fires in Australia by 7.4%, concentrated in the north and in the arid interior. Amongst the many repercussions of increased fire activity due to longer fire seasons and increased lightning would be a release of more greenhouse gases to the atmosphere, intensifying the warming trend and creating a positive feedback with landscape fire

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