U.S. Joint Fire Science Program


Date of this Version


Document Type



Fire Science Brief, Issue 32, January 2009


US government work.


The Northern Rocky Mountains have sustained wildfi re for centuries. Fires are widespread throughout the region during certain years, most recently in 2000, 2003, 2006, and 2007. However, until very recently there was little understanding of whether such years of widespread fi re occurred prior to the 20th century or of the role of climate in the occurrence of such years. Penny Morgan, Emily Heyerdahl, and Carol Miller used fi re atlases, fi re scars, vegetation, and climate data to address this question. They found that climate is clearly associated with the occurrence of widespread fi res in the Northern Rockies throughout the 20th century and in prior centuries. Years of widespread fi res had warm springs, followed by warm, dry summers. In addition, during the 20th century, widespread fi res occurred during the positive phase of the Pacifi c Decadal Oscillation (PDO). A gap in years of widespread fi re occurred during the mid-20th-century in part because climate conditions were generally not conducive for widespread fi re. Given projections of future climate change, years of widespread fi re are likely to continue to occur. However, simulation results suggest that land management objectives can be met even with substantial increases in fi re activity over 20th-century levels.