Northern California was bracing for a fresh round of electric storms on Sunday, as a wave of wildfires sparked by lightning a week ago looks likely to set records in a state suffering increasingly serious seasonal blazes.

Nearly 600 fires sparked by an unusually fierce series of storms a week ago have since consumed more than 1m acres, or an area nearly a third larger than the state of Rhode Island. Two of the conflagrations have grown to rank among the three biggest ever recorded in California.

Coming even before the official start of the wildfire season, when strong autumn winds fan flames at the end of a long dry season, the unusual August outbreak has been the latest incident to expose what state leaders have blamed on the worsening ravages of climate change.