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After quarried areas, the most effected are the marginal lands,
where the overgrazing and the plowing of this type of land
cover are very intensive. Followed by, in order, irrigated area,
desert rangeland, orchards, rainfed agriculture areas, Western
rangeland, reserved areas, and forests. The third factor
indicating the vegetation degradation is the index of vegetation
cover calculated from the satellite image, where the NDVI can
assist to estimate the distribution of vegetation density over the
study areas.
6.2.4 Salinization
Soil salinity in the study area is the direct result of the irrigation
activity. This means that most important factors relevant to
salinity are ground water quality, productivity of irrigated fields,
soil type and climatic conditions (mainly rainfall and evapo-
transpiration). Examining these factors, it was found that the
irrigated lands are approximately under almost the same
climatic conditions and have same soil characteristics (desert
soil) except in a small area where solonchack soils exist. Also
the agricultural productivity in this case study strongly
correlates with water quality. Thus it is concluded that water
quality is the predominated factor to classify the salinity of
irrigated area. The water quality declined rapidly over time.
This conclusion permitted to classify the salinity of irrigated
lands into three classes: areas irrigated from the earliest times
up to 1985 (considered severely affected by salinity); those area
irrigated from 1985 up to 1989 (moderately affected); and those
area irrigated from 1989 up to 1997(slightly affected).
6.3 General Desertification map
The general desertification map, which synthesize all types of
land degradation, is achieved through the following three steps:
Stepl: Soil erosion map
Wind erosion map and the water map were combined to
produce by overlapping the soil erosion image. This procedure
creates a matrix of 16 combinations possible. As a general
decision rule, the slight degrees of wind erosion and slight of
water erosion are assigned to slight soil erosion, and the very
severe wind erosion combined with very severe water erosion
gives very severe soil erosion, and so on. Applying these rules
to the possible combinations lead to four classes of soil erosion
from slight to very severe.
Step2: combination of soil erosion with vegetation degradation
In this step we integrated the result of soil erosion with the
vegetation degradation map, obtained previously. In the same
manner as for combination of wind erosion and water erosion,
we obtained an intermediate desertification map with four
classes.
Step 3: Integration of salinization
This step is achieved simply by overlapping salinization map
with its different degrees with the result of step 2. The result
shows a general land degradation (desertification) map of the
study area. Figure 3 shows all types of land degradation
including the general desertification map.
7. CONCLUSION
Remote Sensing and Geographic Information System (GIS)
techniques allow the integration of many factors and data layers
with different forms, with potential applications in the design of
new methodologies for dealing with desertification problems.
The accuracy of data entered into the GIS in this study depends
IAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring", Hyderabád, India,2002
largely on the original form of data, whether it is digital satellite
data or hardcopy thematic maps. Other considerations are the
scale and resolution of data.
The layer of Desertification Mapping Units (DMUs) permits the
analysis and assessment of different types of land degradation.
Through this layer we may make queries (equations) about
desertification and others environmental features, and obtain
answers in form of maps, tables or charts. Desertification
analysis and mapping using via remote sensing and GIS
constitutes the originality of this research. There is a big lack in
desertification mapping using remote sensing and GIS, where
few studies were found to map desertification using such tools.
The study concluded that there is need to develop standard
methods and criteria for desertification studies. These methods
must apply remotely sensing data, in such way to map and
assess continuously and periodically land degradation
processes. An important area of research is the simulation of
satellite data (e.g. vegetation index) with desertification
processes.
Finally the statistical results of this study (Table 2) demonstrate
the severity of desertification at all levels. It is suggested that all
parts of the study area are suffering from desertification, mainly
by vegetation degradation process (86% of the study area is
severely to very severely affected), and wind erosion (56% of
study area is severely to very severely affected). One of the
results of this study is the estimation that 12% of the Mafraq
governorate is slightly desertified, 7% is moderately desertified,
35% is severely desertified and 44% is very severely desertified.
Without doubt, these results argue the severity of desertification
in the study area. The study of land characteristics has offered
answers to some serious problems, such as soil salinity, which
is due to the ineffective practices of irrigation and shifting
cultivation. The erosion analysis highlighted environmental
problems, such as the proliferation of quarries in areas better
suited to agriculture.
Table 2 Desertification Assessment by type of land degradation
Desertification Assessment by type of degradation
Degree of Slight | Moderate | High | Very
assessment high
Water Area | 16441 66793 | 18404 | 20628
erosion (he)
% 13.19 5337.) 1476 1..16.35
Wind Area | 30804 20028 | 19338 | 52097
erosion (he)
% 24.71 16.06 | 15.51 | 41.79
Vegetation Area 3610 10488 | 35451 | 72717
degradation (he)
227
% 2.90 8.41 | 28.43 | 58.33
Salinization | Area 7240 3636 5030 0
(he)
% 5.81 2.92 4.03 0
Soil erosion | Area 24258 22152 | 61376 | 14480
(he)
% 19.46 17,77} 49.23 | 1161
General Area | 106360 8644 | 43822 | 54328
Assessment (he)
% 12.41 6.93 | 35.15 |} 43.58
REFERENCES
CNT (Centre National De Teledetection, Tunis), 1992, Project
of Hill Dam Sites Location (Report).
