A 78- Year Climatology of Aeolian Dust in El Paso, Texas: Relationship to Drought and Large-Scale Teleconnections

Thomas Gill 1, David J. Novlan2, Joe D. Collins1, Marisela Montelongo1, Matthew Baddock3
1University of Texas, Dept. of Geological Sciences, El Paso, Texas, USA, 2National Weather Service, Santa Teresa, New Mexico, USA, 3Loughborough University, Dept. of Geography, Loughborough, Leicestershire, UK

El Paso, Texas is the largest city in the USA portion of the Chihuahuan Desert, and arguably the dustiest city in North America.  Its metropolitan area (contiguous with Ciudad Juarez, Mexico: combined population ~2.1 million) lies ≤ 200 km away from numerous dust-emissive playas, alluvial deposits, and sand sheets, and experiences frequent strong synoptic-scale winds under clear skies during the dry season (typically November- May) and haboob-producing thunderstorm outflows during the North American Monsoon (typically July- September). The USA National Weather Service documented and catalogued 1,966 individual dust or sand weather events, with associated meteorological data, at El Paso between 1932 and 2009.  Here, we relate these data to meteorology, seasonality, drought status (PDSI) and planetary-scale climate indicators including ENSO and the PDO.

Although dust events happen throughout the year, the number of events and total duration of dusty conditions during both dry and wet years and regardless of ENSO or PDO state are strongly peaked in March and April (the peak dry, windy season) and reach a minimum in August and September (peak of the rainy season), showing the dominant relationship of dust to annual weather patterns.  Dust hours maximized during the 1930s Dust Bowl and 1950s drought, and were minimal during the 1980s- early 1990s wet period, although the number of discrete dust events peaked in the 2000s (more frequent but shorter in duration). Overall dust frequency and duration is strongly skewed towards negative PDSI categories, further confirming that dust in El Paso is generally associated with drought.  However, dust events are most prevalent during only mild to moderate drought conditions (even more so when concurrent with La Niņa episodes) and are relatively less frequent during extreme droughts (which may be generally less windy): however, dust events which do occur during extreme drought periods are the longest-lasting.  Blowing dust still occurs during many wet and El Niņo periods, suggesting aeolian activity in the northern Chihuahuan Desert is transport-capacity and sediment-availability limited.  Of the four wind quadrants (NE, SE, SW, NE), southwest winds are dominantly associated with dust events at El Paso regardless of PDSI and ENSO category: southwest winds prevail generally in the region regardless of dustiness, and have an open fetch to highly wind- erodible landforms. However, dust arrives with NE winds 19% and 22% of the time during moderate and severe droughts respectively, indicating long-distance advection of dust from the Great Plains (especially during the 1930s Dust Bowl).  Back trajectories (modelled with HYSPLIT) confirm the predominance of dust with air masses arriving from the southwest across the erodible lands of northwest Mexico’s Chihuahuan and Sonoran Deserts, regardless of ENSO or PDO state.