The extreme fires ravaging California, which have burned over 1,500 structures and killed at least 15 people, are not a coincidence. Evidence and long-term climate projections indicate that such apocalyptic fires result from just the right combination of ingredients. Mashable journalist Andrew Freedman breaks down the biggest factors that led to California’s latest disaster and uncovers how climate change helped set the stage:

• A Wet Winter Followed by a Hot Summer 

The firestorm is occurring on the heels of the warmest summer in California’s history, which featured numerous record-shattering heatwaves, including one that set a new all-time heat record for downtown San Francisco, at 106 degrees Fahrenheit. Five months of unusually hot and dry weather following the state’s record wet winter ensured a ready supply of combustible vegetation. The frequency of these extreme conditions is becoming the new normal , as climate change alters long-term climate and raises the odds of both extreme precipitation events and heat waves.

• Multi-Year Drought

In addition, the longer-term context of record multi-drought just a year ago reduced the net ‘fuel moistures’ (the amount of water in vegetation) were at or near record low values when the wind-driven fires ignited, which likely contributed to the extreme rate of spread and the likelihood of spot fire ignition during the firestorm, according to Daniel Swain, a climate scientist at UCLA.

• ‘Diablo Winds’

Perhaps the biggest factor: hot, dry, and powerful winds from inland areas to the coast that help rapidly propel the fires across lands. Such air currents are known as “Diablo” winds in Northern California, and Santa Ana winds in southern parts of the state. As Swain explains, “These winds were a necessary condition for the fires’ rapid spread, but the broader climate context certainly set the stage for the event to be as bad as it was.”