Search

Low-frequency changes (decades to years) in precipitation related to the El Nino-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) are known to influence wildfire variability across the southwest United States. Little work has been done to identify whether daily fire weather variability, also important to wildfire activity, is influenced by these same climatic phenomena. This study identifies the synoptic climatological conditions associated with extreme fire weather events in the Southwest and constructs an extreme fire weather frequency data set for the period of 1958–2003 using a logistic regression technique. Interannual changes in extreme fire weather day frequencies are not linearly correlated with either ENSO or PDO, but do show significant deviations from expected values when grouped by PDO phase (positive or negative) and further subgrouped by ENSO state (La Nina, El Nino or neutral). A higher number of extreme fire weather days occur during the negative phase of the PDO, especially when accompanied by a La Nina event. Copyright © 2010 Royal Meteorological Society

Extreme fire-weather conditions are usually thought of as discrete events rather than part of a continuum of meteorological and climatological variability. This study uses a synoptic climatological approach (weather typing) to examine the seasonal climatology of extreme fire-weather conditions across the southwest United States (Arizona and New Mexico) during the period of 1988–2003. Three key circulation patterns representing broad southwesterly flow and large geopotential height gradients are associated with over 80% of the extreme fire-weather days identified in this study. Seasonal changes in relative humidity levels, strength of height gradient, and geopotential heights all modulate the relationship between these key circulation patterns and extreme fire-weather days. Examination of daily incident summaries for three recent wildfires (May 2000, June 2002 and June 2003) shows that wildfire activity can be strongly regulated by these critical fire-weather circulation patterns. Copyright  2006 Royal Meteorological Society.