California is once again confronting a rapidly escalating wildfire season fuelled by extreme heat, drying vegetation, drought and strong winds.

As of 24 July, the state has recorded more than 3,800 wildfires so far this year, burning approximately 79,000 hectares. The largest active blaze, in Lassen County, had grown to more than 28,000 hectares.

The immediate images are familiar to Australians: towering smoke columns and orange skies. But these wildfires are not simply the result of hot summer weather. They are driven by a chain of interacting climatic, environmental and human factors.

In Australia, a powerful El Niño and the possible emergence of a positive Indian Ocean Dipole would bring drier, warmer weather. This could create similarly dangerous conditions in southern and eastern Australia this spring and summer.

A hot, dry landscape primed to burn

In southern California, persistent drought, abundant grass growth and low coastal moisture have accelerated the drying of vegetation. In the north of the state, early–season dryness and the development of “flash drought” conditions have pushed some landscapes towards critical fire danger.

As temperatures rise, warm air can draw more moisture from plants and soils. This means that even if it rains, vegetation cannot replace the water it loses. Even living plants can dry enough to burn fiercely.

Warm nights — a product of global heating — are another concern. Previously, cool and humid overnight conditions give firefighters a chance to strengthen containment lines. When nights........

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