Source : Landsat image interpretation dated (19:5),
v
Saeed Mosmar Alawad, Saeed
Satellite images analysis for land use/land cover mapping that refers to transformation of sensed data into
usable and readable information. According to Lillisand and Keifer (1994) there are two methods for extracting
information from remote sensing data Visual image interpretation and image analysis using computer environment.
Visual interpretation was followed using simple equipment and facilities (e.g. optical magnifiers, light table,
ProComp etc. For land use/land cover mapping classification system were established and developed to arrange
information into groups and mapping units. Using this system land use/land cover categories can be recognized,
recorded and tabulated. The step results in multi date land use/land cover and drainage network maps.
Image interpretation for soil degradation refers to the mapping of areas that affected by process of removal of
the topsoil by water. The final map zones suffer from erosion hazards in 1993.
Map production after field verification is stop taken for map compilation, edditing, layout and design.
The final stage is the analysis of the cartographic products for assessing and monitoring the land degradation.
6. Results and discussion
Complex database displayed in cartographic forms as shown in figures 2 and 3 shows the land use/land cover changes
over the two decades. Changes are present statistically in table 1. Overlay of the two maps, the baseline land use/land
cover map dated 1973 superimposed with 1993 land use/land cover map confirmed the trends in land use/land cover
changes and practices. Figures 4 and 5 displayed the drainage densities and system in the area. Figure 6 present areas
suffer from erosion hazards in 1993.
Table 1: Land use/land cover changes between 1973-1993 in Gedaref Region
Land use/land cover categories | Areain 1973 | Areain 1993 | %ofareain 1973 | % of area in 1993
Agricultural land
-Semi mechanized farm
*demarcated 1259020 2012855 14.4 28.0
* undemarcated 0042480 2292900 00.5 26.0
- Small scale rainfed farm 1201130 1504755 13.7 17.0
Sub total 2502630 5810510 28.6 66.2
Forest land
-Natural forest 4464666 1366381 51.1 15.9
-Reserved forest 0147775 0261800 01.7 03.0
Sub total 4612441 1678181 52.8 18.9
Grazing land 1007830 0729470 11.5 08.3
Kerrib land 0360750 0300520 042 05.3
Jebel (hills) pedmont/bareland 0256350 0271320 02.9 03.1
Total area 8740001 8740001 100 100
Note: percentage is out of the total land of the study area 8740001 Feddans
The results represent two factors that occur in the region, which affect land resources. These are:
1. Land use/land cover changes:
Examination of the cartographic and statistical data shows very clear distinct features, of the spread of semi-mechanized
farm and deforestation at the expense of natural forest. The increasing needs for agricultural lands, fuel and woody
materials for commercial and domestic uses aggravated by economy-political forces are the main causes of the land
use/land cover changes and land degradation in the region. The changes are abrupt extending over larger areas. The
(1973) land use/land cover map (Figure 2) shows that most of the Gedaref Region carried open to dense natural
vegetation. The transformation of natural forest to traditional rainfed namely burned system of cultivation (Hariq
system of rainfed cultivation) was concentrated along the central part of the region and mainly around settlements. On
the contrary 1993 land use/land cover map (Figure 3) indicated substantial increases and encroachments of semi
mechanized rainfed cultivation in the expenses of natural green cover. The maps indicated that land clearing for rainfed
cultivation practices is progressing from north and is approaching southwards towards river Rahad. The semi-
mechanized area has already invaded the buffer zone ofthe Dinder Game Reserved Area (Park) the main and well-
known natural game reserved aréa in the Sudan. Calculated areas of land use/land cover according to planimetric
measurement shown in table 1 disclosed that the rainfed areas increased to cover about 66%of the total area in 1993
compared to 28% in 1973. In 1973 forest area covered about 52.8% of the total area in the region. This has decreased to
cover only 18.9% in 1993 map, with a decrease of about 46% in twenty years. The grazing land has also been degraded
by the invasion of the rainfed cultivation. In 1973 map pastureland covered about 11.5% of the total area. By 1993 it
covered about 8.3% with a decrease of 26% in twenty years.
2. Surface runoff erosion: : :
Precipitation, vegetation cover, soil characteristics and topography are the factors that affecting surface water erosion
(Hudson, 1986). Increasing in drainage density was performed forces in assessing water erosion because it is generally
correlated to be the most simple and an effective tools using remotely sensed data. The consequences of land use/land
cover changes 1973-1993 was a reduction in infiltration capacity of the soils and increasing over land flows that
International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000. 1297
