RELATIONS AMONG DUST EVENTS, WIND SPEED, AND PRECIPITATION AT MESQUITE LAKE PLAYA, MOJAVE DESERT

Dust events in the Mojave Desert are responsible for periodically diminished regional air quality, highway traffic accidents, and potential effects on human health. Mesquite Lake playa straddles the California/Nevada border to the southwest of Las Vegas, NV and is a source of dust that raises PM10 levels in that city. To identify the conditions associated with dust from Mesquite Lake playa, several field campaigns have been conducted and two cameras with anemometers were established to record dust emission. Based on camera records from January, 2008 to May, 2010, more frequent and intense dust events occur in April, and to a lesser degree, March and May. A monthly dust score was calculated based on the qualitative, ordinal intensity of dust events and their frequency. Correlations between the dust score and wind parameters (monthly median of hourly maximum wind speeds or monthly median of daily average wind speeds) were generally low (<0.1). Correlations between the dust score and same-month precipitation or the standard precipitation index found negative correlations at timescales of one month (-0.38 to -0.47) and positive correlations at timescales of 6-12 months (0.43 to 0.5). These associations indicate that rainfall suppresses dust in the short term and enhances dust at time scales from six months to a year after rains. Surface measurements taken several times during the study period found that moderately thick (3-14 mm) surface crusts form following wet periods, possibly due to re-precipitation of salts and gypsum. These measurements found that during the dustiest time of the year (April), the most actively deflating areas had the thinnest (or non-existent) crusts. Based on these measurements and correlations, it is likely that precipitation influences the vulnerability of the surface by stimulating the formation of protective crusts at the surface that then break down over a period of months to leave the surface vulnerable to wind erosion. These results indicate that the wind-erosion vulnerability of playa surfaces is dynamic and highly dependent on moisture in surface sediments. Therefore, climate cycles such as ENSO can be significant drivers of the temporal variability in intensity and timing of dust emitted from playas in the Mojave Desert.