The study suggested that the transformation may already be underway. The Southwestern United States has been in drought since 2000, although tree-ring records show there have been far drier periods during the last millennium.

Scientists said more persistent drought would inevitably lead to more fires, as long as intermittent periods of moisture allowed vegetation to grow as fodder for flames.

In Southern California, hillsides were ripe for fire because big rains two years ago allowed vegetation to flourish, then severe drought during the last year dried it out.

Norman Miller, a climate scientist at Lawrence Berkeley National Laboratories, published an analysis last year in Geophysical Research Letters predicting that rising temperatures, fueled by greenhouse gas emissions, would eventually push peak Santa Ana winds from mid-October to late November.

That could, over decades, make fires worse by giving the landscape more time to dry out. Global warming, he said, could intensify wind flow by increasing the difference between inland and coastal temperatures.