Wildfires across the western United States have been getting bigger and more frequent over the last 30 years, according to a new study. The number of wildfires over 1,000 acres in size in the region stretching from Nebraska to California increased by a rate of seven fires a year from 1984 to 2011, according to a study accepted for publication in Geophysical Research Letters, a journal published by the American Geophysical Union.