RELATIONSHIPS OF SUBALPINE FOREST FIRES IN THE COLORADO FRONT RANGE TO INTERANNUAL AND MULTI-DECADAL SCALE CLIMATIC VARIATION

SIBOLD, J.S. AND VEBLEN, T.T.

Department of Geography, University of Colorado, Boulder

The purpose of this study was to identify relationships of wildfire variability in subalpine forests in the Colorado Front Range to climate variability, broad-scale climate drivers, and phase combinations of climate drivers at interannual to centennial time scales. We compared widespread fire years for the subalpine zone of southern Rocky Mountain National Park with climate variables including measures of drought and climate drivers including El Niño-Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), and the Atlantic Multidecadal Oscillation (AMO). Large fire years are significantly related to extreme drought conditions, the La Niña phase of ENSO, the negative phase of the PDO, and the positive phase of the AMO. The co-occurrence of the phase combination of La Niña-negative PDO-positive AMO is more important to fire occurrence than the individual influences of the climate patterns. Low-frequency trends in the occurrence of this climate driver phase combination, resulting from trends in the AMO, is the primary driver of periods of high fire occurrence (1700-1789 and 1851-1919) and low fire occurrence (1790-1850). The controlling influence of AMO on drought and years of large fires in the subalpine forests of the Colorado Front Range probably applies to an extensive area in western North America.