Desertification is one of the most serious environmental and socio-economic problems of
our time. Desertification describes circumstances of land degradation in arid, semi-arid
and dry sub-humid regions resulting from the climate variation and human activities. The
fundamental goal of this thesis was to monitor the extend and severity of the land
degradation and examine climate variability and change in the Butana area of northeastern
Sudan.
To explore the climate variability and climate change in terms of rainfall, temperature
and the aridity index for the period from 1941 to 2004, the monthly and annual time
series for four weather stations (El Gadaref, Halfa, Wad Medani and Shambat) across the
Butana area were analysed. The trend of the rainfall at Wad Medani and Shambat shows
significant decline, while that of Halfa and El Gadaref does not show a significant
decrease or increase. The Cumulative Rainfall Departure (CRD) was used to detect the
periods of abrupt changes in the rainfall series. A significant decrease in the annual
rainfall was observed at Shambat (p = 0.00135) and Wad Medani (p = 0.0005) from 1968
to 1987, there after the rainfall amount is close to the long-term mean. In El Gadaref there
was a decline in the annual rainfall from 1971 to 1974 (p = 0.35) but it was not
significant, with a recovery from 1975 to 1982 to a value higher than the long-term mean,
followed by another downward turn from 1983 to 1994. In Halfa there was a significant
decrease (p = 0.0304) from 1982 to 1993. The trends of maximum and minimum
temperature were examined for the summer (March-May), autumn (June-October) and
winter (November-February) seasons for the four weather stations. At Halfa and Shambat
the trend of maximum and minimum summer and winter temperature was increasing but not significant, while in Wad Medani there was a significant increase for summer and
winter minimum temperatures. El Gadaref station showed a significant increase in
maximum and minimum temperature (p = 0.00005, p = 0.00016) respectively. The
minimum autumn temperature for Halfa increased significantly, while this was the case
for both the minimum and maximum autumn temperature at Shambat and Wad Medani.
This significant increase in temperature, associated with autumn, is partly due to dry
conditions observed during the late 1960s.
The relationship between 8 km2 AVHRR/NDVI and rainfall data (1981-2003) was tested
in the Butana area. The relationship was strong between the peak NDVI (end of August
through the beginning of September) and cumulative July/August rainfall, but weak
relationships resulted when annual rainfall and cumulative NDVI were used. The
Departure Average Vegetation method showed that the area had a high percentage of
departure, reaching about 40% of the long-term average during the drought years and the
NDVI recovered during the following year if the rainfall was above average. There were
increased trends in NDVI in the study area during the period from 1992 to 2003, despite
some years during this period having higher departure although that departure was less
than for the period 1981-1991. To monitor the impact of human activities on land
degradation it is essential to remove the effects of rainfall on vegetation cover. Using the
Residual Trend Method the differences between the observed peak NDVI and the peak
NDVI predicted by the rainfall was calculated for each pixel. This method identified
degraded areas that exhibit negative trends in NDVI. The human impact is more clear in
the northern part.
Satellite imagery provides an opportunity to undertake routine natural resource
monitoring for mapping land degradation over a large area such as Butana over a long
time period. This facilitates efficient decision making for resource management. Five
classes of land use were achieved using unsupervised classification, whereafter an image
difference technique was applied for 1987-1996 and 1987-2000. This analysis showed
that the bare soil and eroded land increased by 3-7% while the vegetated area decreased
by 3-6%. Also when comparing the aerial photographs (1960s and 1980s) for Shareif Baraket, Kamlin and El Maseid with Landsat images (2000) severe degradation of the
vegetation cover was visible at all the three sites.
The Moving Standard Deviation Index (MSDI) is calculated by performing a 3Ã3 moving
standard deviation window across the band 3 Landsat images (1987, 2000). MSDI proved
to be a powerful indicator of landscape condition for the study area. The MSDI increased
considerably from 1987 to 2000, especially for Sufeiya, Sobagh and Banat areas, which
are referred to as severely degraded sites in the literature. The Bare Soil Index (BSI)
supports the finding from the MSDI. The BSI for the degraded sites Sufeiya, Sobagh and
Banat increased from 0-8 in 1987 to 32-40 in 2000. The image difference of the BSI
indicated that the index increased by about 14-43 over the 13 years.
A Microsoft Excel macro was used to write the algorithms for a decision support tool
relating the factors that trigger and propagate desertification in arid and semi-arid areas.
This was named âTashurâ. Rainfall, aridity index and NDVI were used to evaluate the
condition of the landscape. If these three parameters alone were not sufficient to make a
decision, then soil and human activity parameters need to be consulted for more reliable
decision making. This simple and concise decision support tool is expected to provide
guidelines to planners and decision makers.
Different ecosystems in the Butana area are subjected to various forms of site
degradation. The desertification has led to sand encroachment and to accelerated
development of dunes and also increased the water erosion in the northern part of the
area. The area has also been subjected to a vegetation cover transformation. Pastures have
deteriorated seriously in quality and quantity, but in many parts the degradation is still
reversible if land use and water point sites are organized.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-07302007-140717 |
| Date | 30 July 2007 |
| Creators | Elhag, Muna Mohamed |
| Contributors | Prof S Walker |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-07302007-140717/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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