Dry thunderstorms, Bushfires and Climate Change

The Wikipedia entry for dry thunderstorms refers mainly to North America. They note that in “areas where trees or other vegetation are present, there is little to no rain [in the dry storm] that can prevent the lightning from causing them to catch fire. Storm winds also fan the fire and firestorm, causing it to spread more quickly” and “dry thunderstorms generally occur in deserts or places where the lower layers of the atmosphere usually contain little water vapor…They are common during the summer months across much of western North America…” The entry makes no connection between this phenomenon and climate change.

But humidity was identified as a critical factor in Australian bushfires by Tom Beer et al in a 1987 paper which examined the relationship between the enhanced the Greenhouse effect and our bushfires. As predicted this century has seen a strong rise in the frequency and size of damaging bushfires in the east and south-east. In particular the fires of 2003, 2006/7, 2009 and 2019 have all been ‘unprecedented’ in some way. Of these fires 2006/7 was an, early then, December start and this year a November start – earlier still and indicative of a lengthening fire season.

On 8 January 2003 eighty-seven fires in the mountains were started by lightning in dry thunderstorms. Something similar, though not as large, has just occurred across east Gippsland and the north east. As in 2003 conditions were favourable for the rapid spread of fires with severe rainfall deficiencies over a number of years and a warm to hot November. The numerous blazes started by the lightning strikes created a logistical nightmare for fire-fighting authorities. The obvious response has been to fight those parts of the fire that threaten property. The downside of this is that those fires that are in remote, rugged country receive little or no attention and are allowed to grow in size and these can massively expand rapidly with the arrival of hot windy conditions.

Climate predictions have long been for warmer dryer conditions to increase. Studies of thunderstorms in relation to climate change have mostly been about their increasing frequency, severity, winds and hail size. An Australian study in 2013(Allen et al ) noted “significant increases to the frequency of severe thunderstorm environments will likely occur for northern and eastern Australia in a warmed climate”. From this we may draw the tentative conclusion that ‘dry thunderstorms’ will also increase.

A more recent study on ‘climate event attribution’ observed “overall bushfire risk depends on fuel type, fuel amount, fuel dryness, weather conditions and ignition sources including lightning and humans”. Beyond this I have been unable to find any evidence supporting links between dry thunderstorms, climate change and bushfire ignition.*

But we may ask were the current fires, and those of 2003, at least partially started by climate change, via these dry storms?  In 2003 the black humour went something along the lines of “the good news is there are less fires today, the bad news is they have joined together”. Fortunately for Gippsland, the conditions now (end of November) and weather predictions are benign for the immediate future, but a number of the fires are already large and may continue burning for some time.

*An article on Tasmanian bushfires earlier this year that confirms this link has been brought to my attention post publication. See here.