From 1960, when the center's tally begins, through 2010, wildfires throughout the US burned an average of 4.2 million acres a year. Between 2000 and 2010, however, the average rose to 6.6 million acres a year. Six of the last 11 years saw from 7 million to nearly 10 million acres burned. Between 1960 and 2000, only two years reached the 6-million-acre mark.
So far this calendar year, wildfires in the US have burned 3.1 million acres, according to the NIFC.
Conditions leading to this year's fires along the southern tier include the persistence of long-term droughts, which in the Southwest in particular have lasted for a decade, although with some minor breaks, notes Tom Swetnam, a fire ecologist at the University of Arizona's Laboratory of Tree Ring Research.
In addition, he says, La Nina conditions – cooler than normal surface water – in the tropical Pacific, in place since October, have tended to drive storm tracks along the northern US. This has tended to further dry an already parched landscape.