Southern Great Plains Wildfire Outbreaks

Abstract

Destructive wildfire outbreaks are a preeminent natural hazard on the grass-dominated landscape of the southern Great Plains. These southern Great Plains wildfire outbreaks (SGPWOs) are characterized by tens of wildfires that evolve on spatial and temporal scales closely tied to the passage of midlatitude cyclones when dormant herbaceous vegetation is particularly dry and abundant. Ten SGPWOs inflicted tragic losses of life and property across eastern New Mexico, west Texas, and Oklahoma between December 2005 and April 2009. This study reviews the conditions that promoted these dangerous phenomena. Texas A&M; Forest Service records reveal that enhanced seasonal wildfire activity and increased potential for SGPWOs typically occurs during El Niño Southern Oscillation cold phases (La Niña), especially when preceded by positive growing-season rainfall anomalies. The antecedent state of predominately fine grassland vegetative fuels associated with SGPWOs is quantified per Energy Release Component (ERC, fuel model G). Average ERC values >50 (>70th percentile) supported the 2005-2009 SGPWOs on the Great Plains of Texas. Meteorological composites that quantify mean synoptic patterns during SGPWOs are generated via Rapid Update Cycle analyses, and averaged vertical temperature, moisture, and wind profiles are presented. Further analyses of subsynoptic low and midlevel tropospheric temperatures and winds illustrate a tendency for wildfires to occur near 2-m and 850-hPa thermal ridges when overspread by 500-hPa wind maxima. The juxtaposition of these atmospheric features appears to be a useful meso-α-scale predictor of heightened wildfire risks. Recognition of the presented seasonal indicators toward a fire-prone regime influenced strategic preparations for the historic 2011 Texas wildfires. Operational use of composite pattern recognition-based forecasts in tactical decision support is demonstrated for the 27 February 2011 “firestorm”, a particularly damaging SGPWO during an unprecedented fire season. Average ERC values >75 (>95th percentile) additionally supported prolonged burn periods with the passage of subsequent fire outbreak-bearing weather systems during the spring of 2011. Lastly, seasonal trends and the chronology of climatic and environmental signals prior to SGPWOs are highlighted, per a summary of conditions that preceded all of the 2005-2011 episodes.