Most of the great deserts of the world occurred as a result of natural processes that occurred over long intervals of time. According to NASA online, desertification refers to the reduction in productivity on the land that cannot be reversed when the land cannot support the same plant growth it had in the past, and the change is permanent on a human time scale. Human activities on the natural environment cause desertification (ACSAD, 2004). Since early 1920s, the desertification is an environmental problem that has raised interest of environmentalists as well as the scientific community globally. However, only in these last decades the problem has been considered a serious environmental issue because of the social-economic impacts (Xue and Shukla, 1993). Desertification has a greater impact in developing countries, where poor agricultural practices lead to extremely serious consequences of draught and famine (Sardinha, 2008). However, desertification also affects the developed nations because of unsustainable practices in Agriculture and Forestry sectors combined with poor land management and weak government policies (Clark, 2001).
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Lack of proper action will cause many people worldwide be displaced by desertification and land degradation in the next few years (Desertification in the Arab Region, 2007).
Aim of the study
This literature review aims to examine the current scientific knowledge of desertification: the causes of desertification and implication of desertification. The research discusses desertification processes in the Western Tabuk province, Saudi Arabia. The main objective was to investigate and analyze desertification processes through using Landsat TM imagery from 1988 and to 1999 and ancillary data, in conjunction with fieldwork to detect vegetation sites and human impact. The results showed that spectral reflectance for dry soil and desert vegetation was considered an indication of desertification. Ratio vegetation index (RVI) was utilized to produce the image of vegetation change and delineate degraded areas from non-degraded area. Grazing and woodcutting have been observed to be leading to affect the certain vegetation sites in the study area (Al-Zookah, 2002).
Definition of desertification
Desertification is caused by natural occurrences, such as drought and human induced activities. Climatic variations make the fragile soils vulnerable to erosion and desertification (Dragan, et al, 2005). According to UNCCD (1994), desertification refers to land degradation in arid, semi-arid and sub-humid regions. These conditions result from various factors such as climatic variations and anthropogenic activities (Chandra and Ghosh, 2006). Other definitions refer to processes that alter the productive deserts into non-productive deserts due to unsustainable and poor land-management practices (El Hassan, 2004).
The consequences of desertification are diverse. For instance, it reduces the ability of land to support life, affecting biodiversity, agricultural crops and humans. The reduction in plant cover as a result of desertification results into soil erosion (Emgaili, 2003).
Human induced activities that result into desertification include over cultivation, overgrazing, deforestation and poor water management (UNCCD, 2004). Overgrazing animals and removal of vegetation cover for firewood collection accelerated desertification. On the other hand, overstocking of animals makes soil become compacted by hard-footed animals, hence becoming less able to soak up rain exposing the soils to agents of erosion (Pereira, et al, 2006). This further reduces plant growth. High demands for the limited surface and groundwater reserves lead to overuse and further salination (The Joint Committee on Environment and Development in the Arab Region (2007).
Desertification is a serious environmental problem that threatens the future of human beings. Desertification usually affects the vegetation cover and increased soil erosion as the bare soil is exposed to wind and water erosion. The resulting soil degradation that commonly occurs in regions of grazing or marginal rain-fed farming leads to desertification. These create desert-like conditions that might be irreversible (Xue, et al, 1991). The impacts of desertification lead to serious threat to the world especially the developing countries and cause long-term problems in economic activity, human health and famine as well as food security. Moreover, desertification affects the physical infrastructure, natural resources and the environment, national and global security. Desertification occurs as a result of increase in human population, intensive subsistence of agriculture practices, deforestation and overgrazing.
In Africa the problem of desertification is complex and overlapping problem. Approximately two thirds of the continent is classified as deserts or drylands (Viterbo and Beljaars, 1995). According to Abouzed (1998), it is believed that the Sahara desert has been advancing towards the Sahel. The widespread of desertification led to many deaths of men and livestock. Desertification led to social and economic tragedies represented by famine and economic collapse. Moreover, this led to immense economic loses as well as a threat to social organizations from villages to the national level (Joly, 1990). In the last two decades satellites have begun to provide the global monitoring that is of considerable importance to improving the understanding of desertification. Moreover, Landsat images indicated changes in the susceptibility of the land to desertification. Most studies using the Landsat data assist in demonstrating the impact of desertification on people and animals on the Earth. There are different types of remote-sensing systems, land-monitoring networks and global data bases of field observations that are necessary in understanding the processes and problems of desertification.
In China, remote sensing techniques such as Landsat TM and Landsat ET have been used to detect processes and impacts of desertification. The index of the GSI (grain size index) that is proposed in this study can be of significant assistance in detecting the abundant fine-sand area and to indicate the potential for monitoring the desertification process in arid regions (Hill, 2004). In America and Australia desertification is also a critical environmental problem. In Latin America desertification has expanded in both Brazil and Mexico (UNCED, 1992). For instance, in Mexico the land area comprises of a large share of ASALS (United Nations and the Economic and Social Commission for Western Asia, 2005). The impact of desertification has forced many people to migrate to cities in search for jobs because the arable lands had lost productivity due to desertification. In many countries overpopulation of human and livestock has accelerated desertification (United Nations, Economic and Social Affairs, 2002). In Latin America, the widespread of desertification has caused many people to migrate to Brazil and Mexico. A larger portion of lnd is affected by desertification, and degradation of arable land has increased to approximately 60 million hectares.
In the Middle East a large stretch of land from the Atlantic to the Persian Gulf is classified as drylands or deserts (Arab League and Arab Organization for Agricultural Development, 2003). Dry lands cover over 60% of the region. In Iran many people migrated from drylands because of their reduced productivity and the encroachment of the desert conditions. Desertification caused massive losses of livestock in Iran and profoundly affected the economic prosperity of the region since people depend on the goats and sheep for economic activities. According to a report from Iran’s Anti-Desertification Organization, sand storms buried many villages in Sistan-Baluchistan in 2002. Thus, many people were forced to abandon the drifting sands that also covered the grazing areas. Livestock were affected, hence depriving the villagers of their source of livelihood. In Iran most people abandoned their homes because of the encroachment of deserts. Desertification spread to other countries such as Nigeria, where famers and herders were forced to migrate from their villages in search for safer places where they got squeezed in productive lands. Moreover, desertification forced many people to be environmental refugees while other migrated to other cities or abroad.
In Saudi Arabia, there were debates concerning the causes and impacts of desertification in the Tabuk region using Landsat TM imagery. These debates were started from 1988 to 1999 with ancillary data that were employed to detect and monitor desertification. It was discovered that spectral reflectance for dray soil and desert vegetation indicated the occurrence of desertification. Scientists used a Ratio Vegetation Index ((RVI) that produced images of vegetation change. Moreover, it was found that the changes in vegetation were a result of overgrazing and woodcutting which affected the vegetation cover (AL-Balooshi, 2003). The fluctuations in rainfall on various regions and the lack of restrictions on the carrying capacity of grazing lands in a grazing area over a given period, or lack of resilience period during a certain period of up to four times contributed to the deterioration of the pasture quality as well as quantity.
Desertification in Tabuk Province
The climatic condition in Saudi Arabia is classified as arid with an exception of the Asir province. The rainfall is sparse with an average annual of approximately 100 mm. more that half of the total area of Saudi Arabia being desert. The region is characterized by significant amounts of rainfall that occurs in the northern, western, and eastern region, during winter. Saudi Arabia is mostly experiencing scarcity of natural water resources with low irregular rainfall that increasing the problems of desertification. However, despite the awareness of desertification in Saudi Arabia, the country is yet to put into place. The problem of desertification in Saudi Arabia is not a new phenomenon but has grown to be a serious environmental threat, particularly to the delicate desert ecosystem, as well as, the urban and the industrial area. This had been aggravated by the movement of sand. According to AL-Balooshi (2003), a relatively small area that receives the most rain is experiencing congestion as the majority of the urban and economic centres are centred that are concentrated in areas which contain forests and are utilized as fruit farms. Al-Zookah, (2000), the area is mostly characterized by tropical warm climates except for the high mountain ranges and the Northern areas situated at the North of latitude 30o N where the climate are moderate. According to Abouzed (1998), in 2000, the demand for water was 127 m3 but is expected to increase to 176 m3 by 2035. The application of remote sensing provides a wide range of opportunities as well as advantages in the monitoring of desertification monitoring since it provides a large scale, repetitive and an accurate coverage. In the Tabuk Province, there are several factors that contribute to desertification. Increase in population increases pressure on the limited natural resources and the indiscriminate exploitation without consideration about sustainability; therefore lack of specialized and competent staff in the field of natural resources protection and management as well as in combating. The increase in the population size and requirements caused by the major imbalances in the environment. The major causes of desertification are overstocking that leads to overgrazing, overexploitation of land, poor agricultural practices and spread of mechanized farming, particularly in the marginal areas as well as the misuse of water resources (The Joint Committee on Environment and Development in the Arab Region (2007).
Natural causes of desertification
The Tabuk province mostly experiences scarcity of water and other natural resources. In the consequences of dry periods, the water sources are depleted and deteriorate in quality. Moreover, through the geologic times climate change has also played a critical role in the emergence of desertification in the ASALS that are characterized by poor vegetation cover. Dry lands in the Tabuk area receive fluctuated amounts of rainfall hence leading to a draught mostly associated with land degradation. Previous work on factors causing desertification: land desertification is the result of environmental degradation influenced by an arid and windy climate. Human causes of desertification include population that leads to serious imbalances in the environment. Anthropogenic activities that have dramatically led to desertification include cutting down vegetation, overstocking that leads to overgrazing, overexploitation of land, poor irrigation, as well as spread of mechanized farming, particularly in the marginal areas.
Desertification detection and monitoring in Tabuk Province using remote sensing and GIS
The technique involving GIS and remote sensing provides effective information and significant contributions in the assessment and monitoring of desertification processes by offering a spatial information required for a regional scale analysis of the relationship between climate change and desertification processes. The processes require proper measurement as well as interpretation. These could also be evaluated to a large extent with the help of remote sensing techniques and GIS. When using the Landsat, it is vital to use images that cover the study area. These images are obtained from the internet. The images are then subjected to various digital processes and analyses at the Remote Sensing Laboratory. This is done to enable a suitable image in the creation of a composite colour. The Landsat composite colours are the Near Infra-Red, Red and Blue that can be combined to make false-colour composite images. In this case the colour bands are combined to make false-composites. This makes image analysis and involves calculation of histogram for each of the bands followed by linear stretching. The colour composites are created to provide a better visual impression of the image surface in comparison with the use of a single band. Changes in the composition of the top soil as well as vegetation cover compositions can be identified through analysis of the colour composites. Thus the concept of the land use and land cover changes can be analyzed for the applicability in ASALs environmental change indicators through the use of remote sensing and GIS technologies and change detection techniques. Moreover, there are other GIS techniques that are used in the analysis and mapping applications as well as i the monitoring of natural processes. These techniques are derived from a high resolution satellite imagery derived from satellite sensors like such QuickBird, IKONOS, SPOT-5, GeoEye-1, WorldView-2 as well as, Worldview-1.
History of monitoring the technique used on GIS and remote sensing
In the ancient times, the issue of desertification assessment had been approached from a site specific perspective. Initially, there had been a lot of difficulties in understanding desertification due to the difficulties in understanding the link between what is understood to be desertification and the measurements have been obscured. However, the historical development of GIS can be traced back in early 1960’s when researchers began to make use of a computer based GIS. The initial development began in the North America, and its development was initiated in Canada by the Canadian Geographic Information System (CGIS). Other stakeholders included the United State Bureau of Census, the United States Geological Survey, and the Harvard Laboratory for Computer Graphics and Environs, the Natural Resource Research Centre (NREC) as well as the Department of Environments of UK. Remote sensing refers to the collection of data concerning an object from a distance. Man and other animals undertake this task by using their eyes or through the sense of smell as well as hearing. Initially, geographers applied remote sensing to measure phenomena that lies deep within the earths crust, the biosphere, hydrosphere as well as the atmosphere. The application of remote sensing began in 1960, where its application employed space satellites that had an extended view of the earth’s surface. a second revolution of remote sensing technology that incorporated the Landsat satellites, in the 1970’s. Since then, the application of remote sensing technology had been used in the monitoring the changes that occur in land and water resources.
Other developments were also initiated in India where major developments occurred in the last ten years in the initial stages. The technique was applied for the management of nature, however, presently; India has made tremendous development in the application of GIS in areas such as monitoring of infrastructural development, business market applications as well as facility management. Currently, the application of GIS technology incorporates a common data base operation like statistical analysis with unique visualization, as well as, the benefits of geographic analysis offered by maps. These characteristics make GIS to be different from other technologies and make it helpful various applications for explaining events, predicting outcomes, and in planning strategies. In addition, other attempts to quantify desertification took place for the United Nations Conference on Desertification (UNCOD, 1944) in response to the 1970’s drought of the Sahel region. Most studies suggested that the southern limit of the Sahara was expanding by more than 5.5 km per year. The discussion concluded that over 3900 million hectares were experiencing the encroachment of desert (Nahal, 1987). Despite the development of a provisional methodology for assessing and monitoring desertification by the FAO and UNEP in the 1980s, reliable data were still lacking at national and global scales and global assessments were still not based on systematic measurements. There were many challenges by a series of detailed remote sensing studies that showed the extent to which the location of desert margins can change in response to rainfall variability (Werth and Avissar, 2002).
Implications of desertification phenomenon affecting Tabuk province
Desertification has impacts on affected populations and affected countries (Wieringa, 1986). Desertification has some negative environmental, economic and social impacts. Impacts associated with desertification may be direct and indirect, all of which affect human life (Niama, 2003). For instance, desertification affects soil fertility as well as chemical and physical properties of the soil. The production per hectare in the Tabuk province has significantly reduced (Viterbo and Beljaars, 1995). In addition, the deterioration of the pastoral lands causes a reduction in the productivity of livestock as well as the productivity of other animals, hence reducing the production of meat and milk. Economically desertification affects the forest lands and the natural pasture hence reduces the economy of the region through the reduction of income from the natural based products. Environmental impacts associated with desertification include the formation of sand dunes and the encroachment of sand on urban areas and farms as well as roads (Tolba et al, 2001). Other environmental impacts include air pollution, dust and reduction of the biodiversity due to reduction of natural habitats for biodiversity as well as microorganisms. Degradation of natural environments leads to the migration of pastoralists, nomads and residents of rural areas to urban areas in search for better place. Migration affects economic as well as social lives of the nomads since it affects the younger generation who are the active and energetic groups of the society (Millennium Ecosystem Assessment, 2005).
Modelling the impact of climate change and desertification in to the future, 30-50 years
Modelling desertification in the future is faced by challenge since there is lack of an adequate reference situation against which the actual desertification can be compared. Moreover, the challenges appear as a result of the difficulties that appear when desertification operates through structural rather than functional ecosystems. However, in the next three to five decades, desertification will increase at a higher rate since, it is projected that the world is loosing approximately 6 million of its land to desertification yearly. It is predicted that these lands are different from the naturally occurring deserts because the causes are attributed to anthropogenic activities. Since, roughly 70 m2 is the minimum area of land required feed each individual, it is projected that even a medium-rate increase in population increase will lead to land scarcity for many people by the year 2050. The forecasting on the spread of desertification depends on availability to model interactions between land surface and atmosphere in the global climate models. In the future it is necessary to have high quality model-derived climate projections that will be crucial for sustainable environmental management. The improved techniques will improve reporting of the crucial components of the land surface system in the standard model output (Menson, 1998).