David McNew, Reuters

A STRING of wildfires is raging in California. Six separate blazes have together scorched more than 55,000 hectares of land. As of 8 December, nearly 200,000 people had been evacuated.

The largest blaze is the Thomas fire (pictured), which has burned around 45,000 hectares. The long exposure in this photo shows how strong winds are spreading the embers between trees.


California is prone to wildfires, but 2017 may end up being the worst year on record, with enormous fires also breaking out in October.

A new analysis by Alexandra Syphard of the Conservation Biology Institute in Oregon and her colleagues examined the factors that have triggered US wildfires from 1972 to 2010. The team found that both climate and human activities have played significant roles in Californian wildfires over the years (PNAS, DOI: 10.1073/pnas.1713885114).

Climate is a key factor in California’s wildfire risk, agrees Stefan Doerr of Swansea University in the UK. “Superimpose a rather prolonged drought and the strong seasonal winds”, both of which have happened this year, he says, and “these fires are not unexpected”.

Humans have also exacerbated the problem in places, Doerr says, for example “by planting highly flammable alien tree species that produce very effective embers, such as palms”.

Photographer

David McNew, Reuters

This article appeared in print under the headline “Stoking the embers”