As shown, the actual number of 2013 fire incidents is close to matching a historic low of the available dataset and represents a 60% reduction from the 30-year average ending in 1999.
Regarding total acres burnt in 2013 (YTD - Dec. 2013), the 4+ million acres is well below the 5-year moving average but remains higher than the 30-year simple average ending 1999. To put the year's 4+ million into context, a single Colorado fire in 1898 raged across 4 counties (10,088 square miles) representing some 6.4 million acres.
On the chart is a dashed black line indicating the year 1998. As the dataset reveals, the total yearly acres burnt started a continuous climb after 1997, peaking in 2006. Every year since 1998 has seen total acres consumed by fire exceeding the 30-year average ending in 1999.
Was this increase in total acres burnt due to the modern global warming affecting the U.S.?
The actual temperature data indicates the opposite. Since 1998, the U.S. temperature trend has been a negative 3.2F degrees/century - yes, that is a minus trend covering the 16-year period from December 1997 through November 2013. And as this recent article about Alaska's cooling since the turn of the century confirms, its forest fires have not been a result of 21st century "global warming."
In contrast, the U.S. did have a significant warming trend from the span of 1970 to 1997. The huge number of forest fire incidents during the late 1970s and early 1980s is clearly evident in the above chart. What is also clearly evident is that Republican President Ronald Reagan was able to mitigate with dispatch the awful malaise of the previous Democrat administration's (President Jimmy Carter) forest fires. ;-)