Dust emission and deposition in southwestern United States - integrated field, remote sensing, and modeling studies to evaluate response to climatic variability and land use

Document Type

Article

Journal/Book Title/Conference

Desertification in the Third Millennium, Proceedings of an international conference, February 12-15, 2000, Dubai, United Arab Emerites

First Page

271

Publisher

Swets & Zeitlinger, The Netherlands

Last Page

282

Publication Date

2000

Abstract

Geomorphic processes in arid regions are particularly sensitive to climatic variability. In this context, integrated shldies are being conducted to understand the response of dust emission and deposition to climatic and land-use change in the arid southwestern United States. Several approaches are taken to monitor wind erosion and characterize modem dust - its sources, flux, and composition - to document the potential for desertification under future climatic conditions. Wind erosion is monitored at ecologically sensitive sites, using meteorological stations that measure sand flux within the saltation layer. Dust deposition is also monitored at these and many other sites using different types of dust collectors. In addition, new remote sensing methods detect the location, frequency, magnitude, and duration of large dust-emission events. Remotely sensed images ofvegetation change, combined with those that illustrate high soil reflectivity, complement dust-detection methods to identify areas especially susceptible to wind erosion. Dust trapped in collectors and in snow is characterized for its physical, mineralogic, and chemical properties. Combined with soil and weather data, such characterization sheds light on: (1) the relation between dust storms and synoptic climatic conditions; (2) the importance of Owens (dry) Lake (California) as a dominant source of southwestern U.S. dust. for as much as 400 km downwind; (3) the impacts of human disturbances in the desert, revealed by signatures of agricultural and construction dust; and (4) the composition and flux of regional background dust composition and flux. Past dust flux is studied from late Quaternary eolian deposits, partly using a new combinaticn of magnetic and chemical methods developed to recognize eoFan dust in soils and surficial deposits over large regions. Such studies have applications to understanding current plant distribution, substrates for biologic soil crust, and paleoenvironmental histories of ecosystems.

A wind-erosion model based on wind strength, atmospheric shear stress on the surface, and almospheric stability is being developed. This model will be constrained by remote sensing and ground-based observations and will then be linked with a regional climate model and interactive vegetation package to forecast how various climatic and land-use scenarios interact with critical wind speeds required to move surface materials. \Ve will attempt to answer the following questions: How does wind strength vary with natural climate cycles on decadal and cenhlry time scales? To what extent will winds become stronger or weaker under future climate scenarios? How have soil moisture and vegetation changes affected wind erosion in the past, and what can we expect in the future? As an example of possible future conditions, projections of doubled atmospheric CO2 (above preindustrial levels) for the southwestern U.S. suggest a decrease in winter soil moisture. which may enhance wind erosion.

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