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The nation is closing in on its worst wildfire season in recorded history, with nearly 9.8 million acres already burned -- the equivalent of Massachusetts, Connecticut, Rhode Island and part of New Hampshire going up in flames.

Two large fires and more than 160 smaller ones remain active, and more fires are expected to be reported before the month ends. Together, they're likely to push the 2015 total past the record 9.87 million acres burned in 2006.

The extent of scorched earth reflects a warming trend that has made the United States considerably drier, scientists and fire expects say, with less mountain snowpack particularly in Alaska and the southwest.

Agriculture Secretary Tom Vilsack said in September that $200 million a week was spent to battle wildfires nationwide. All told, some 30,000 people in at least a dozen states have been deployed for that effort - the largest force since 2000.

And to date, 13 firefighters have lost their lives across the country. More than 4,600 structures have been destroyed.