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| LIBYA: Land Cover Change Analysis |
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The land cover change assessment of Libya was conducted as one of the
activities of the "Mapping
of Natural Resources for Agricultural Use and Planning in Libya" (LIB/00/004)
project.
A comparative change detection analysis between the land cover visual
interpretation of 1980's, 1990's and 2000's Landsat dataset (MSS, TM, ETM)
and Ikonos satellite data was performed.
Four study areas representing the more sensitive situations to changes
in Libya were selected:
- Tripoli, to assess the impact of urbanization and estimate
the amount of tree plantation loss due to anthropogenic factors.
- Jafara Plain, to assess the rangeland changes due to pastoralism
(overgrazing).
- Tawarga, to assess the changes of the coastal and the sabkha areas.
- Jebel Akhdar, to assess the changes occurred on a portion of its
natural vegetation due to the anthropic impact.
In order to set up a methodology to be applied on the other selected areas,
priority was given to Tripoli, since it was the most interesting and
accessible area. The anthropic impact in terms of population and
urban expansion has been studied with the maximum care according to
the data available. Below are some details of the analysis over Tripoli.
Process
The first step was to collect all the available ancillary information,
in terms of images, historical data and personal knowledge.
The images used as interpretation basis for this application are:
- Landsat MSS of 29-01-1976
- Landsat TM of 29-03-1989
- Landsat ETM of 5-08-2001
In addition to the August image, the 2000's data set has been enriched
with two more images: a Landsat ETM of 23-03-2001 and an Ikonos of April
2002 (see figure below).
A portion of a high resolution Ikonos image was used to carry out the
interpretation of most of the Tripoli urban area. The area covered by the
Ikonos was mapped at a scale of 1:5.000, reaching a very detailed
interpretation especially as concern the urban area.
Results
The first comparison on the changes occurred in the Tripoli area was
obviously focused on the expansion of the urban area. Comparing the
images of the three available data, the immediate effect is chromatic,
clearly displayed by the increase of the urban-grey colour all around
Tripoli. Watching the numbers of the chart below, we realize that the
urban area of Tripoli doubled in the last 25 years; in fact from
the 11.587 ha of 1976, it reaches 22.534 ha in 2001. This is the
first worrying data on the expansion of the Tripoli population.
The increase of Tripoli population also means an increasing food demand.
The agricultural area shows a constant expansion following the urban
area spreading out. But, if the urban expansion affected especially the
agricultural land around Tripoli, the agricultural land grew up mainly
at the expenses of tree plantations. The chart below shows the evolution
over the three dates.
The clear victims of both urban and agriculture expansion around Tripoli
are the tree plantations. The disappearance of the tree plantations is
also linked to other reasons, always referable to the anthropic impact.
In fact, a portion of the plantations have been cut to produce firewood.
In some cases, the original tree plantation has been transformed in
rangeland with a low percentage of sparse trees remaining, as a mark of
the former tree plantation. Anyway, most of the previous tree plantations
have been replaced by new agricultural land.
The chart below provides summary figures and distribution over the three
dates:
In 1976 around Tripoli there were about 25 thousand hectares of tree
plantations. In 1989 the situation was already worst, since it decreased
of about 6 thousand hectares. But the drastic change in the tree plantation
coverage of the Tripoli area is between 1989 and 2001, when the remaining
tree plantations measure only 6 thousand hectares. It means that, on
average, more than 1 thousand hectares of trees per year disappeared
between 1989 and 2001. In few words, the total amount of tree plantations
around Tripoli decreased of three fourth in 25 years.
Click here to
display a summary of the change assessment results for each aggregated
land cover class.
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