Mapping and Monitoring salinity
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Maps showing areas affected by salinity can be
produced from satellite images |
Dryland salinity poses a major threat to many rural industries around
Australia. Farmer surveys have indicated that more than 1.2 million ha of productive land
are affected by salinity across Australia, with a further 1.6 million ha at risk. It is
estimated that $243 million a year is lost in agricultural production.
The Australian Bureau of Statistics conducted a farmer survey in 1993 which reported
that more than 500 000 ha (3.1%) of the land cleared for farming in Western Australia was
saline. Some shires reported that up to 9% of the previously arable land had been lost,
while individual property owners reported that up to 40% of their properties were
salt-affected.
These surveys are likely to underestimate the problem. new property owners do not
always know when areas have become saline. Emerging sites with reduced yields or which
support a cover of salt-tolerant species such as barley grass and saltbush are not always
included in farmer estimates of salt-affected land. While these surveys provide
statistical summaries of the amount of salt-affected land on a shire basis, they don't
produce maps of where the salinity is, where it is spreading, and how fast it is
spreading.
Salt-affected land has been mapped in different parts of the Western Australian
wheatbelt using Landsat TM satellite imagery.
Carefully calibrated sequences of images from 1987 to 1994 have been used to develop
procedures for discriminating between land in persistently poor condition due to salinity
and land exhibiting short-term decreases in productivity due to other factors.
Regional maps of salt-affected land can be produced by choosing appropriate image dates
within the growing season. The image data from two seasons have been combined with
landform maps to further reduce the confusion between seasonal and management effects.
These image maps can be compared through time to show where and by how much the
salt-affected areas are changing.
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Salinity change map 1987 - 1994:
red areas were saline in 1987
yellow areas became saline in 1990
blue areas became saline in 1994 |
On a more local scale, a series of calibrated images can be used to show the sequence
of changes that occur as known saline regions expand. The following images show an
expanding area of salt-affected land, and the salinity change map of the area
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1990 Landsat TM image
bands 7,5,4 in red, green, blue
the saline region shows as grey and blue |
1993 Landsat TM image
bands 7,5,4 in red, green, blue
the extended saline region shows as grey and blue |
Salinity change map 1987-94:
red areas were saline in 1987
yellow areas became saline in 1990
blue areas became saline in 1994 |
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