Impacts of Climate Change and Land Use on the Southwestern United States
Wind Erosion Vulnerability and Rainfall Mapping in the Southwestern United States

Eolian Mapping

Many factors influence the amount of wind erosion that occurs. Two critical factors are the percent of vegetation cover and the type of surface soils. Using satellite digital multispectral data, a simple model has been developed that allows an image to be generated that emphasizes areas with low vegetation density and high reflectance soils. Generally, this automatically maps two important eolian erosion parameters (i.e., amount of vegetation cover/density and general surface soil type). In arid and semi-arid environments the soils most vulnerable to wind erosion usually have low vegetation cover and bright reflectance. At this stage, the bright reflectance aspect is mostly an empirical observation and a more scientifically based explanation, such as the relationship of soil brightness to gain size and soil type, has not been examined yet. An image is generated using this model that shows areas where these two conditions occur together. In this image, various shades of yellow indicate different levels of low vegetation density and high reflectance soils, and serve as a guide to the relative level of erosion potential/vulnerability to wind. These can be used to generate an Eolian Mapping Index (EMI) value at each pixel. In the Landsat MSS images shown below, the brighter yellows have a higher erosion potential than the more dull yellows, with the non-yellows having little or no wind erosion potential.

Click on each of these images to see larger versions (1000K, 786K)
Northern Arizona -- MSS Yuma -- MSS

The image results shown above are for the Northern Arizona (left image) and Yuma, Arizona (right image) test sites. The brighter yellows have a higher eolian erosion potential than do the more dull yellows, and the non-yellow areas have little, if any, eolian erosion potential.

Current analysis and field work are used to evaluate the accuracy of the model by validating and quantifying wind erosion susceptibility. Several sites in Northern Arizona that show transitions between eolian and non-eolian materials, or between eolian and vegetated eolian materials are being studied to:

  1. Determine the ability of the eolian algorithm to resolve sharp transitions.

  2. Determine in a quantitative way whether or not surface material is vulnerable to eolian erosion. This is done using a 500-micrometer sieve to measure the first 1 cm of the soil to compute the percentage of material less than 500-micrometer in diameter. Particles with less than 500-micron diameter are readily eroded by the wind; therefore, this gives an approximate measure of its eolian composition and related eolian vulnerability. These data will be correlated with the various eolian erosion image products being generated using the Landsat MSS and TM images.

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