in the Puna area:
0 vegetation cover deterioration;
0 water erosion;
0 wind erosion;
0 salinization and alcalinization.
From the point of view of their quantitative importance, one
process can be mainly identified: water erosion.
This problem decreases land productivity . Changes due to
human action develop fast over short time intervals in
response to precipitation events of high intensity, becoming
evident as rills and gullies or as broad bare surfaces due to
intense sheetflow.
A management plan for this basin should be made on the
basis of a proper description and diagnosis of the different
levels of water erosion present in the area. At the same time
it should include appropiate provisions for the regulation of
land use in general and for the socio-economic development
of the population .Those activities should be promoted from
the point of view of the cultural traditions and pattern
behaviour of the inhabitants . The use of preventive measures
is very important in the areas not yet affected by
degradation processes or showing a minimum degree of
erosion.
It was not possible to separate the degrees of water ero-
sion in TM color composites of single bands (2,4,5 ;
3,4,5:3,4,7 )or in single indexes such as SAVI (8) or band
3/4 ratio.
The objective of this research was to develop an
enhacement to discriminate the earlier stages of water
erosion through Landsat Thematic Mapper images in
this particular region of Argentina because none of the
usual enhacements were good enough.
2.1.Background:
The Miraflores river basin is located between 22 and 25
Southern latitude and 65 to 67 Western longitude in the
Argentine Puna region .
The climate is semi-arid showing wide temperature
fluctuations between day and night. Winter is the cold and
almost dry season, with a mean rainfall of 10 mm; while
summer is relatively warm and rainy (290 mm)
The arid conditions produce a scant vegetation cover
which offers negligible protection against erosion.
The high erodability of the soils, also enhances the action of
the winds and torrential rains from November to March.
The semiarid steppe is mainly composed of tussock gras-
ses (Pennisetum chilense;Festuca scirpifolia) and shrubs
(Parastrephia | lepydophylla; Baccharis boliviensis and
Tetraglochin cristatum) with an average height between 40
and 80 cm.
In Winter the vegetation covers 40 to 60 % of the
ground. In Summer ( rainy season) the vegetation cover
increases up to 80%
Since the pre-colombian times, this region has been
subjected to the practices of shifting breeding of native
camelids,llamas and vicuñas in open fields. The few crops -
are grown in narrow terraces on the foot hills .
Spanish colonization and the beginning of sheep and beef
cattle augment the impact over this ecosystem with little
resilience . The introduction of pastures such as Eragrostis
curvula and the use of fences have increased the number of
cattle heards, especially beef leading to overgrazing, which
is considered the principal erosive factor (11) in this region.
3. METHODS:
3.1.Identifying water erosion degrees in the field:
After the stratification of the Miraflores river basin,
seven sampling areas (6)were choosen according to their
representativity , forty three "test sites"were selected (10). A
correlation test was performed between landfeature reflec-
tance and TM bands.
In RUSLE a subfactor method is used to compute SL as a
function of four subfactors :prior land use,canopy,ground
cover and within- soil effects.
Water erosion features were measured in the field according
to the "Desertification Method" 6).
3.2. Digital Analysis
Two sets of Landsat Thematic Mapper (TM) data were
used, one from the Winter dry season (October,1991) and
the other from the Summer rainy season (March,1993). Six
bands (except thermal band) from Landsat TM were used
for this study.
A regression analysis was performed with the objective of
384 International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998
sior
3,4,
3/4
