Wind Erosion Vulnerability and Rainfall Mapping in the Southwestern United States
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
Click on each of these images to see larger versions
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:
Determine the ability of the eolian algorithm to resolve sharp
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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