Show simple item record

dc.contributor.advisorWalker, S.
dc.contributor.authorElhag, Muna Mohamed
dc.date.accessioned2015-08-19T12:16:15Z
dc.date.available2015-08-19T12:16:15Z
dc.date.issued2006-11
dc.identifier.urihttp://hdl.handle.net/11660/945
dc.description.abstractEnglish: 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 vi 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 miimum 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 vii 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 3×3 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 ndicated 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 “Tashur”. 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.en_ZA
dc.description.abstractAfrikaans: Verwoestyning is een van die ernstigste omgewings- en sosio-ekonomiese probleme van ons tyd. Verwoestyning beskryf omstandighede van land-degradasie in ariede, semiariede en droë sub-humiede streke wat voortspruit uit klimaatsveranderings en menslike aktiwiteite. Die fundamentele doel van hierdie verhandeling was om die graad en omvang van die land-degradasie te monitor en om klimaatsveranderlikheid en -verandering in die Butana-gebied van noordoos Soedan te ondersoek. Die klimaatsveranderlikheid en –verandering ten opsigte van reënval, temperatuur en ariditeitsindeks is ondersoek vir die tydperk wat strek van 1941 tot 2004 deur die maandelikse en jaarlikse tydreeks van vier weerstasies (El Gadaref, Halfa, Wad Medani en Shambat) regoor die Butana-gebied te ontleed. Die neiging vir reënval by Wad Medani en Shambat dui betekenisvolle afname, terwyl dié van Halfa en El Gadaref geen noemenswaardige afname of toename toon nie. Die Kumulatiewe Reënvalafwyking (KRA) was gebruik om die tydperke van skielike veranderinge in die reënval tydreeks uit te wys. ʼn Beduidende toename in die jaarlikse reënval was by Shambat (p = 0.00135) en Wad Medani (p = 0.0005) waargeneem van 1968 tot 1987, waarna die reënval na aan die lang-termyn gemiddeld is. In El Gadaref was daar ʼn afname in die jaarlikse reënval van 1971 tot 1974 (p = 0.35), maar dit was nie betekenisvol nie, met ʼn herstel van 1975 tot 1982 na ʼn waarde hoër as die lang-termyn gemiddeld, gevolg deur ʼn verdere afwaartse neiging tussen 1983 en 1994. In Halfa was daar ʼn beduidende afname (p = 0.0304) van 1982 tot 1993. Die neigings van maksimum en minimum temperature is ondersoek vir die ix somer- (Maart-Mei), herfs- (Junie-Oktober) en winterseisoene (November-Februarie) vir die vier weerstasies. By Halfa en Shambat was daar ʼn nie-betekenisvolle maar stygende neiging in die maksimum en minimum somer- en wintertemperature, terwyl ʼn betekenisvolle toename wel in Wad Medani waargeneem is. El Gadaref het ʼn betekenisvolle toename in maksimum en minimum temperature (p = 0.00005, p = 0.00016) respektiewelik, getoon. Die minimum herfstemperature vir Halfa het beduidend toegeneem, terwyl dit die geval vir beide die minimum en maksimum herfstemperature by Shambat en Wad Medani was. Hierdie beduidende styging in temperature wat met herfs geassosieer word, is deels te wyte aan droë toestande wat gedurende die laat 1960s voorgekom het. Die verwantskap tussen 8 km2 AVHRR/NDVI en reënvaldata (1981-2003) is getoets in die Butana-gebied. Die verwantskap was sterk tussen die piek-NDVI (einde van Augustus tot begin September) en kumulatiewe Julie/Augustus reënval, maar swak wanneer jaarlikse reënval en kumulatiewe NDVI gebruik is. Die Afwyking Gemiddelde Plantegroei Metode het getoon dat die gebied ʼn hoë afwykingspersentasie het wat sowat 40% van die lang-termyn gemiddeld gedurende die droogtejare bereik en dat die NDVI gedurende die volgende jaar herstel het wanneer die reënval bo-gemiddeld was. Daar was stygende neigings in NDVI in die studiegebied gedurende die tydperk wat strek van 1992 tot 2003 al was daar sommige jare in hierdie tydperk wat hoër afwykings getoon het en hoewel daardie afwyking minder was as wat gedurende 1981-1991 waargeneem is. Om die impak van menslike aktiwiteite op land-degradasie te monitor, is dit noodsaaklik om die invloede van reënval op plantegroeibedekkings te verwyder. Deur gebruik te maak van die Residuele Neigingsmetode is die verskille tussen die waargenome piek-NDVI en die reënvalgebaseerde piek-NDVI bereken vir elke beeldelement. Hierdie metode het gedegradeerde areas uitgewys wat negatiewe neigings in NDVI het. Die menslike impak is duideliker in die noordelike deel te bespeur.Satellietbeelde verskaf die geleentheid om roetine monitering van natuurlike hulpbronne vir die kartering van land-degradasie oor ʼn groot gebied soos Butana oor ʼn lang tydperk te ondergaan. Dit bewerkstellig effektiewe besluitneming vir hulpbronbestuur. Vyf klasse van landgebruik is met behulp van onbegeleide klassifikasie daargestel, waarna ʼn x beeldverskiltegniek vir 1987-1996 en 1987-2000 toegepas is. Die ontleding het getoon dat die kaal en geërodeerde grond met 3-7% toegeneem het, terwyl di plantegroeibedekte area afgeneem het met 3-6%. Wanneer die lugfotos (1960s en 1980s) vir Shareif Baraket, Kamlin en El Maseid met Landsatbeelde (2000) vergelyk is, is daar gevind dat ernstige degradasie van die plantegroeibedekking in die drie lokaliteite voorgekom het. Die Bewegende Standaardafwykingsindeks (BSAI) is bereken deur ʼn 3×3 standaardafwyking venster oor die band 3 Landsatbeeld (1987, 2000) te beweeg. BSAI het geblyk om ʼn kragtige indikator van landskaptoestand vir die studiegebied te wees. Die BSAI het aansienlik toegeneem van 1987 tot 2000, veral vir Sufeiya, Sobagh en Banat-areas, waarna as ernstig gedegradeerde plekke in die literatuur verwys word. Die Kaalgrondindeks (KGI) ondersteun die bevindinge van die BSAI. Die KGI vir die gedegradeerde Sufeiya, Sobagh en Banat het toegeneem van 0-8 in 1987 tot 32-40 in 2000. Die beeldverskil van die KGI het getoon dat die indeks met sowat 14-43 toegeneem het oor die 13-jaar tydperk. ʼn Microsoft Excel makro, genaamd ‘Tasahur’, is ingespan om die algoritmes te skryf vir die besluitneming ondersteuningshulpmiddel wat die faktore wat tot verwoestyning in ariede en semi-ariede gebiede aanleiding gee, in berekening bring. Reënval, ariditeitsindeks en NDVI is gebruik om die toestand van die landskap te evalueer. Indien hierdie drie parameters alleen nie voldoende is om ʼn besluit te neem nie, moet grond en menslike aktiwiteitparameters geraadpleeg word om meer betroubare besluite te neem. Daar word verwag dat hierdie eenvoudige en bondige makro ʼn reeks norme aan beplanners en besluitnemers sal bied. In die Butana-gebied is daar verskeie ekosisteme wat aan verskillende vorme van degradasie onderwerp word. Die verwoestyning het gelei tot sandkruip en versnelde duinontwikkeling asook verhoogde watererosie in die noordelike deel van die gebied. Die gebied is ook onderwerp aan ʼn transformasie in die plantegroeibedekking. Weivelde het ernstig agteruit gegaan in terme van kwaliteit en kwantiteit, maar in baie dele is die degradasie steeds omkeerbaar indien landgebruik en waterpunte georganiseer word.
dc.language.isoenen_ZA
dc.publisherUniversity of the Free Stateen_ZA
dc.subjectDesertification -- Sudan -- Butanaen_ZA
dc.subjectArid regions -- Sudan -- Butanaen_ZA
dc.subjectClimatic changes -- Sudan -- Butanaen_ZA
dc.subjectThesis (Ph.D. (Agrometeorology))--University of the Free State, 2006en_ZA
dc.titleCauses and impact of desertification in the Butana Area of Sudanen_ZA
dc.typeThesisen_ZA
dc.rights.holderUniversity of the Free Stateen_ZA


Files in this item

Thumbnail

This item appears in the following Collection(s)

Show simple item record