The University of Arizona

Droughts and Wildfires in Western U.S. Rangelands

John Derek Scasta, John R. Weir, Michael C. Stambaugh


• Because fire activity fluctuates with short- and long-term term weather and climate trends, understanding trends relative to climate forecasts is critical to mitigating the loss of life and property and rapid vegetation state changes.
• Through the analysis of charcoal and trees scars, historical droughts and fire patterns can be quantified retrospectively for hundreds of years. This evidence suggests that generally fire was most frequent during warm-dry periods as opposed to cool-moist periods. However, arid regions may see an increase of fire activity with an increase of moisture due to inherent fuel load limitations.
• Using federal wildfire and weather data from 2002 to 2015 for New Mexico, Nevada, Oklahoma, and Wyoming, we demonstrate that the worst wildfire activity occurred after average or above average precipitation years followed by drought in Oklahoma and Wyoming. Nevada wildfire activity was correlated with precipitation the preceding year, and NewMexico wildfire activity was not correlated with annual
precipitation or preceding year precipitation.
• The effects of future drought on fire intensity and severity are projected to be highly variable because they are both a function of fuel load. However, the potential for very large wildfires is predicted to increase; fire weather is expected to create hotter and drier conditions that start earlier and last longer; and the relative changes may be most noticeable in cooler regions that are of higher latitude and elevation.

Keywords: climate cycles, disturbance, fire, forest, rangeland, weather variability.

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