The first Alaska wildfire of 2016 broke out in late February, followed by a second there just eight days later. New Mexico has had 140 fires this year, double the number in the same period last year, fueled by one of the warmest, driest winters on record. And on the border of Arizona and California this month, helicopters dumped water on flames so intense that they jumped the Colorado River, forcing the evacuation of two recreational vehicle parks. Fires, once largely confined to a single season, have become a continual threat in some places, burning earlier and later in the year, in the United States and abroad. They have ignited in the West during the winter and well into the fall, have arrived earlier than ever in Canada and have burned without interruption in Australia for almost 12 months.