Abstract
Lightning strikes are pervasive, however, their distributions vary both spatially and in time, resulting in a complex pattern of lightning-ignited wildfires. Over the last decades, lightning-ignited wildfires have become an increasing threat in south-east Australia. Lightning in combination with drought conditions preceding the fire season can increase probability of sustained ignitions. In this study, we investigate spatial and seasonal patterns in cloud-to-ground lightning strikes in the island state of Tasmania using data from the Global Position and Tracking System (GPATS) for the period January 2011 to June 2019. The annual number of lightning strikes and the ratio of negative to positive lightning (78:22 overall) were considerably different from one year to the next. There was an average of 80 lightning days per year, however, 50% of lightning strikes were concentrated over just four days. Most lightning strikes were observed in the west and north of the state consistent with topography and wind patterns. We searched the whole population of lightning strikes for those most likely to cause wildfires up to 72 h before fire detection and within 10 km of the ignition point derived from in situ fire ignition records. Only 70% of lightning ignitions were matched up with lightning records. The lightning ignition efficiency per stroke/flash was also estimated, showing an annual average efficiency of 0.24% ignition per lightning stroke with a seasonal maximum during summer. The lightning ignition efficiency as a function of different fuel types also highlighted the role of buttongrass moorland (0.39%) in wildfire incidents across Tasmania. Understanding lightning climatology provides vital information about lightning characteristics that influence the probability that an individual stroke causes ignition over a particular landscape. This research provides fire agencies with valuable information to minimize the potential impacts of lightning-induced wildfires through early detection and effective response.
Highlights
Lightning is a weather phenomenon that is episodic and highly variable in space and time [1]
Spatial Distribution The northern half of Tasmania experiences a larger number of CG lightning strikes compared to the southern part (Figure 2)
Geographical and seasonal variability of lightning activity over Tasmania is dominated by activity over the Western and Northern areas where the typical north-westerly to southwesterly airflow, combined with topographic influences [23] resulted in a clear seasonal signal reaching a maximum in the summer months (Figure 2)
Summary
Lightning is a weather phenomenon that is episodic and highly variable in space and time [1]. Wildfires have already caused extensive damage and concern, and an increase in fire danger or changes in the frequency, intensity, or timing of fires, will have substantial effects on natural systems [11] and human communities [12]. Individual weather elements directly influence ignition potential, largescale atmospheric features and processes are associated with lightning occurrence [13]. Lightning activity is formed due to development of atmospheric instability and to thermodynamic processes which influence its frequency and intensity [14,15]. Lightning activity is projected to increase with higher temperature and continuing climate change [16,17,18,19,20]. Topography in conjunction with favorable synoptic weather systems may trigger convection [22] resulting in thunderstorms [23] and lightning [24]
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