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Desertification - time for an assessment?
Abstract
UNEP considers desertification to be one of the major environmental problems of our time. According to UNEP, 35% of the world's land surface is currently at risk and more than 20 million ha are reduced annually to near or complete uselessness. The desertification phenomenon is considered to be mainly man-made. The prevailing concept of desertification, status and rate of change has been seriously challenged during the 1980s by a growing number of individuals, research groups and international organisations. It has even been questioned whether desertification is actually occurring and the word "myth' has been mentioned. There is a lack of data to substantiate the hypothesis of a secular, mainly man-made, trend towards desertlike conditions in the Sahel. -from Author
... Desertification has been defined as land degradation in arid, semi-arid, and dry sub-humid areas resulting from various factors, including climatic variations and human activities (IPCC, 2001). Another definition of desertification is the spread of desertlike conditions of low biological productivity due to human impact under climatic variations (Helldén, 1991;Reynolds, 2001;Reynolds and Stafford Smith, 2002). ...
... Source: Revised by the author The most severe drought occurred in 1980-1984, and was accompanied by widespread displacement and localised famine. Localised and less severe droughts (affecting between one and five states) were also recorded in 1967-1973, 1987, 1989, 1990, 1991, 1993and 2000(Reynolds, 2001IPCC, 2001). ...
... Recent research has indicated that the most likely cause of these historical droughts was a medium-term (years) change in ocean temperature, rather than local factors such as overgrazing (Helldén, 1991;Reynolds, 2001). Therefore, the potential for such droughts to recur remains. ...
... Despite the confusion and different interpretations of what desertification actually means, alarming numbers on the extent of desertification were published. Estimates of 50% and more of the drylands being affected to some extent by desertification were published [3,4], but these numbers were heavily criticized by scientists actually working in dryland environments [5]. ...
... Others criticized these assessments and found no evidence for large scale movement of the desert boundary but stated that the boundary between the Sahara desert and the more moist Sahelian zone is dynamic. That is, the alternation of dry and wet years results in commensurate movement of the apparent Saharan boundary, driven by rainfall anomalies [5,21,22]. But this view was in its turn criticized by other studies [23,24] which pointed at methodological flaws, and illustrated the controversy about desertification assessment. ...
... Several studies, as summarized in Helldén [5] and Verón et al. [35], have criticized the dramatic desertification numbers of the 1970s, 1980s, and early 1990s [3,4,25,27,28,29]. Research in Sudan neither found any evidence for desert encroachment nor for the establishment of permanent desertlike conditions around villages and water holes [5]. ...
Desertification is defined as land degradation occurring in the global drylands. It is one of the global problems targeted under the Sustainable Development Goals (SDG 15). The aim of this article is to review the history of desertification and to evaluate the scientific evidence for desertification spread and severity. First quantitative estimates of the global extent and severity of desertification were dramatic and resulted in the establishment of the UN Convention to Combat Desertification (UNCCD) in 1994. UNCCD's task is to mitigate the negative impacts of desertification in drylands. Since the late 1990s, science has become increasingly critical towards the role of desertification in sustainable land use and food production. Many of the dramatic global assessments of desertification in the 1970s and 1980s were heavily criticized by scientists working in drylands. The used methodologies and the lack of ground-based evidence gave rise to critical reflections on desertification. Some even called desertification a myth. Later desertification assessments relied on remote sensing imagery and mapped vegetation changes in drylands. No examples of large areas completely degraded were found in the scientific literature. In science, desertification is now perceived as a local feature that certainly exists but is not as devastating as was earlier believed. However, the policy arena continues to stress the severity of the problem. Claims that millions of hectares of once productive land are annually lost due to desertification are regularly made. This highlights the disconnection between science and policy, and there is an urgent need for better dialogue in order to achieve SDG 15.
... Desertification has been defined as land degradation in arid, semi-arid, and dry sub-humid areas resulting from various factors, including climatic variations and human activities (IPCC, 2001). Another definition of desertification is the spread of desertlike conditions of low biological productivity due to human impact under climatic variations (Helldén, 1991;Reynolds, 2001;Reynolds and Stafford Smith, 2002). ...
... Source: Revised by the author The most severe drought occurred in 1980-1984, and was accompanied by widespread displacement and localised famine. Localised and less severe droughts (affecting between one and five states) were also recorded in 1967-1973, 1987, 1989, 1990, 1991, 1993and 2000(Reynolds, 2001IPCC, 2001). ...
... Recent research has indicated that the most likely cause of these historical droughts was a medium-term (years) change in ocean temperature, rather than local factors such as overgrazing (Helldén, 1991;Reynolds, 2001). Therefore, the potential for such droughts to recur remains. ...
Problem statement: Sudan is the largest (2.5 million km2) country most seriously affected by desertification in Africa. The arid and semi-arid lands cover an area of 1.78 million km2, which represents about 72% of the country’s total area1. Sudan has collaborated with and contributed to the International efforts to combat desertification. It is one of the first countries that signed the United Nations Convection to Combat Desertification (UNCCD) and assigned the National Drought and Desertification Control Unit (NDDCU) for the coordination of programmes to mitigate the effects of drought and to combat desertification as a focal point. Since the 1930s, programmes to combat desertification and its component projects and interventions have been launched in Sudan through technical and financial assistance (local and international) to improve land resources, production systems, and protection of the environment. Sudan, like other African countries, needs plant cover: an earlier study for the UN Food and Agriculture Organization (FAO) indicated that Sudan has lost between 250,000 and 1,250,000 hectares of the total area of its forests since 2005; this is the main reason for the expansion of the desertification phenomenon. Therefore, unless serious and immediate action is pursued, the gap between the sustainability of resources and the degree of exploitation will widen further2. Objectives: The objective of this paper is to review the efforts taken by Sudan in combating desertification from governmental and private sectors, and to assess the reasons for the failure of past efforts to combat desertification. Methodology: Previous acts and agreements from National and International sources have been collected. The hazards of desertification and their impacts on economic and social lives have been evaluated. Findings: Many conclusions and lessons emerged from previous experiences of government, NGOs, civil society and private sectors in implementing desertification programmes in Sudan. The analytical review of Sudan desertification policies showed a lack of an intersectoral approach that integrates forestry activities and land use into the social, economic and developmental process of the country. They also lacked linkages to other sectors that use and actually compete for the available natural resources. Values: Therefore it was recommended that capacity building, public awareness, and integration of NGOs, governmental sectors including research institutions, ministries and international organisations is urgently needed.
Keywords: Sudan; desertification; conflicts; environment
... Despite its acknowledged importance, the nature and causes of land degradation have remained stubbornly intractable (Thomas & Middleton 1994;Reynolds et al. 2002;Nicholson 2011a). This has been more evident in the Sahel region of Africa than in any other part of the world where divergent assessments have led to more disagreement and controversy than consensus (Helldén 1991;Nicholson et al. 1998). Much of the controversy, it is generally agreed, have resulted from unwarranted extrapolations from limited data or subjective "expert" opinions, from the lack of a consensus definition, and from the confusion between climate-induced short-term ecosystem dynamics (e.g. ...
... On the other hand, claims of widespread rangeland degradation through overgrazing run counter to long term increases in livestock populations (Sullivan & Rohde 2002;Mortimore & Turner 2005). Extensive studies in the Sudan (Olsson 1985;Ahlcrona 1988;Helldén 1991) (Tucker & Nicholson 1999;Eklundh & Olsson 2003;Herrmann et al. 2005a;Olsson et al. 2005;Heumann et al. 2007a;, suggesting that the perceived widespread degradation in the Sahel can be largely attributed to climate variability and not to irreversible changes in land productivity (Prince et al. 1998;Herrmann et al. 2005a;. Furthermore, interannual variations in agricultural yields per unit cultivated area in Burkina Faso and Nigeria; two countries identified by the GLASOD study as the most degraded in the Sahel; have been found to be strongly related to rainfall variability (Niemeijer & Mazzucato 2002). ...
... provided the opportunity to expand on previous studies of vegetation responses to climate variability Helldén 1991;Olsson & Rapp 1991;Nicholson 2001;Nemani et al. 2003;Herrmann et al. 2005a;Olsson et al. 2005;Helldén & Tottrup 2008;Hiernaux et al. 2009c;Beer et al. 2010). ...
There is a great deal of debate on the extent, causes and even the reality of land degradation in the Sahel. On one hand, extrapolations from field-scale studies suggest widespread and serious reductions in biological productivity threatening the livelihoods of many communities. On the other hand, coarse resolution remote sensing studies consistently reveal a net increase in vegetation production exceeding that expected from the recovery of rainfall following the extreme droughts of the 1970s and 1980s, thus challenging the notion of widespread, subcontinental-scale degradation. Yet, the spatial variations in the rates of vegetation recovery are not fully explained by rainfall trends which suggest additional causative factors. In this dissertation, it is hypothesized that in addition to rainfall other climatic variables and anthropogenic uses of the land have had measurable impacts on vegetation production. It was found that over most of the Sahel, the interannual variability in growing season sum NDVI (used as a proxy of vegetation productivity) was strongly related to rainfall, humidity and temperature while the relationship with rainfall alone was generally weaker. The climate- sum NDVI relationships were used to predict potential NDVI; that is the NDVI expected in response to climate variability alone excluding any human-induced changes in productivity. The differences between predicted and observed NDVI were regressed against time to detect any long term (positive or negative) trends in vegetation productivity. It was found that over most of the Sahel the trends either exceeded or did not significantly depart from what is expected from the trends in climate. However, substantial and spatially contiguous areas (~8% of the total area of the Sahel) were characterized by significant negative trends. To test whether the negative trends were in fact human-induced, they were compared with the available data on population density, land use pressures and land biophysical properties that determine the susceptibility of land to degradation. It was found that the spatial variations in the trends of the residuals were not only well explained by the multiplicity of land use pressures but also by the geography of soil properties and percentage tree cover.
... Nonetheless, Helldén [43] noticed that there is a synergy between climate and anthropic drivers of environmental change in Africa. Assessing the effect of each driver requires supplementing the vegetation trend analyses with a series of LULC change analyses over a long period of time [44]. ...
... Understanding the long-term LULC changes/transitions and the underlying driving factors in Africa may serve as a springboard to identify and separate the effect of climate drivers (e.g., variation in rainfall pattern) of environmental change from anthropic drivers, e.g., expansion of human settlements and croplands [9,10,19]. This is critical in Africa, where it has been established at the local level that anthropic factors may play a central role in land degradation/environmental change, and it is a big challenge to disentangle the effects of anthropic drivers of environmental change from climate drivers [43]. ...
Post-classification change detection was applied to examine the nature of Land Use Land Cover (LULC) transitions in West Africa in three time intervals (1975–2000, 2000–2013, and 1975–2013). Detailed analyses at hotspots coupled with comparison of LULC transitions in the humid and arid regions were undertaken. Climate and anthropic drivers of environmental change were disentangled by the LULC transitions analyses. The results indicated that human-managed LULC types have replaced the natural LULC types. The total vegetation cover declined by −1.6%. Massive net gains in croplands (107.8%) and settlements (140%) at the expense of natural vegetation were detected in the entire period (1975–2013). Settlements expanded in parallel with cropland, which suggests the effort to increase food production to support the increasing population. Expansion of artificial water bodies were detected in the humid regions during the period of 1975–2000. Nonetheless, shrinking of water bodies due to encroachment by wetlands and other vegetation was observed in the arid regions, coupled with net loss in the whole of West Africa. The results indicate deforestation and degradation of natural vegetation and water resources in West Africa. Underlying anthropic drivers and a combination of anthropic and climate drivers were detected. LULC transitions in West Africa are location specific and have both positive and negative implications on the environment. The transitions indicate how processes at the local level, driven by human activities, lead to changes at the continental level and may contribute to global environmental change.
... It mutated to a general discussion of regeneration potential of the ecosystems and the possibilities to find production modes for the necessary food production. Moreover, conservation and nature protection were discussed and great projects were initiated [1][2][3][4][5][6][7][8][9][10][11][12][13]. ...
... The area is structured by a system of wide basins and ridges often topped by mountains of more than 4000 m. Climatically, it is characterised by the Vegetation -Natural and Cultivated Vegetation in a Changing World 6 interaction of the Westafrican monsoon and the tradewinds -see below. However, the most important feature is the general lack of water -a fact, which all living organisms have to cope with. ...
... Monitoring of these changes is ideally accomplished from multi-temporal remotely sensed data [12]. Aerial photographs and multitemporal Landsat data are used to study land use transformation [12,13,14,15]. ...
... Monitoring of these changes is ideally accomplished from multi-temporal remotely sensed data [12]. Aerial photographs and multitemporal Landsat data are used to study land use transformation [12,13,14,15]. The result from multi-temporal remotely sensed images are usually compared with each other to detect the change area and to assess the severity of desertification. ...
... The lack of precipitation puts indigenous species of plants and animals in semi-arid environments under unusual stress and the parallel habitat loss might pose a threat to local biodiversity [16]. Under these circumstances, having educated guesses of the potential vegetation biomass responses in semi-arid landscapes to long term changes in precipitation could serve to put forward the design of adaptation and conservation policies [9]. The estimation of the expected time of transition to a desert state (or bare-soil), as a conceivable measure of those responses, presents difficulties due to the complexities associated with specific water-vegetation systems. ...
... 3. Simulations. We use the stochastic differential equation (9) to simulate the water-vegetation system and obtain averages of the expected time to desertification (see [10] or [13] for a quick or an extensive introduction respectively to the numerical solution of stochastic differential equations). By identifying the parameters of the nondimensional deterministic (non-spatial) model in [12] with the mean field system obtained above (A v = A v (ρ) and A w = A w (ρ), where ρ = (ρ v , ρ w )) we obtain S = AR 1/2 J/L 3/2 andd = M/L, with the meaning and realistic values for these parameters listed in Table 3 Klausmeier assuming that the equilibrium of water (in his deterministic model) is at w * = 75 mm, and then computing the associated evaporation rate given the averaged annual precipitation, [12]. ...
Current climate change trends are affecting the magnitude and recurrence of extreme weather events. In particular, several semi-arid regions around the planet are confronting more intense and prolonged lack of precipitation, slowly transforming part of these regions into deserts in some cases. Although it is documented that a decreasing tendency in precipitation might induce earlier disappearance of vegetation, quantifying the relationship between decrease of precipitation and vegetation endurance remains a challenging task due to the inherent complexities involved in distinct scenarios. In this paper we present a model for precipitation-vegetation dynamics in semi-arid landscapes that can be used to explore numerically the impact of decreasing precipitation trends on appearance of desertification events. The model, a stochastic differential equation approximation derived from a Markov jump process, is used to generate extensive simulations that suggest a relationship between precipitation reduction and the desertification process, which might take several years in some instances. © 2018 American Institute of Mathematical Sciences. All rights reserved.
... The soil degradation occurs in whatever portion of the earth's surface, but it is fixed as "desertification" when it occurs in arid, semi-arid and sub-humid dry areas, derived from the human impact (Helldén, 1992;Reynolds et al., 2007). Desertification is not just a problem of soil loss, but it touches on the stability and development of human populations. ...
... The results of this work show that there was an increase in the vegetation when it increased precipitation and that this period followed a prolonged dry spell between 1980 and 1984. Other studies were supported by the analysis of photographs, field work and implementation normalized index (NDVI), to demonstrate the reversibility of the coating degradation vegetation (Helldén, 1992). ...
The aim of this study is to establish if the San Luis Potosi Plateau (SLPP), which is part of the southern edge of the Chihuahuan Desert, is generating desertification processes, indicating a progression of the desert toward the central part of Mexico. Therefore, we analyzed the temporal evolution of four environmental indicators of desertification: Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), Iron Oxides Index (IO) and Surface Temperature (ST). Landsat TM images are used to cover a period from 1990 to 2011. A new equation of total balance is proposed to generate an image of the overall evolution of each factor which is applied to get a probability map of desertification. The evolution of NDVI, NDWI and IO shows a behavior almost stable over the time. In contrast, the ST shows a slight increase. The outcomes of this study confirm periods of vegetation re-greening and 8.80% of the SLPP has the highest probability to develop desertification. The most affected area is the portion west of the region, and the east and south are the least affected areas. The results suggest a slight advance of the desert, although most of the area doesn’t have the necessary conditions to develop desertification.
... Desert lands occupy over one-third of Earth's terrestrial surface. Land degradation by desertification has devastating consequences, impacting over one-quarter of global land and one-fifth of the world population (Helldén 1991). For example, the Sahara desert alone engulfed as much as 65,000 km 2 of fertile land in the Sahel region, with an average encroachment of 5-6 km per year (Darkoh 1989). ...
... Deserts are mature ecosystems with very low desirable productivity due to severe freshwater limitations prompted by natural and sometimes anthropogenic low-precipitation and high-evaporation conditions, according to The Arid Lands: History, Power, Knowledge (MIT Press, 2016) by Diana K. Davis. Interestingly, the application of aerial and orbital remote sensing technology to major desert and desertification studies only commenced around 1991 [54]. Some experts now suggest a comprehensive reorganization of human civilization's food-production by prioritizing optimal food-growing regions via mechanized farming and irrigation [55]. ...
Resumo: Processos naturais e atividades antropogênicas afetam de forma variável a diversidade climática e ecossistêmica das nações ao redor do Golfo Pérsico-Arábico. O Magic Carpet Giga-Project, proposto como uma contramedida de enfrentamento da aridez dos ambientes regionais, é concebido como uma vasta jangada flutuante com painéis fotovoltaicos, disposta sobre o Golfo. Conectada por cabos elétricos a instalações terrestres, a energia poderia ser fornecida para cidades e para aplicações industriais que incluiriam enormes usinas de dessalinização de água do mar para uso municipal em geral. A adaptação espacial e marítima na forma de caminhos de aproximação e desvios será necessária em razão das rotas marítimas existentes, bem como do acesso adequado às plataformas da indústria petrolífera offshore que pontilham o Golfo. Os macroprojetos "The Line" e "The Loop" serão áreas bem delimitadas com vegetação controlada pelo clima, enquanto o "Magic Carpet" pode se tornar um esteio de dessalinização e fornecimento de eletricidade para a futura infraestrutura básica de cada estado do Golfo. Palavras-chave: Macroengenharia, Arábia Saudita, NEOM, jangada fotovoltaica flutuante, Golfo Pérsico-Arábico, Golfo da Califórnia. Abstract: Natural processes and anthropogenic activities variably affect climate variability and meteorological drought in ecosystem-nations surrounding the Arabian-Persian Gulf. The Magic Carpet Giga-project, proposed as a counter measure to aridification of the regional environments, is envisaged as a vast floating PV-panel studded raft in the Gulf. Connected by electrical cables to land-based facilities, power could be provided for cities and industrial applications that would include enormous seawater desalination plants for municipal and commercial applications. Spatial and sea lane accommodation in the form of approach ways and bypasses will be necessary for designated sea-lanes, as well as according access to in-place offshore petroleum industry platforms dotting the Gulf. "The Line" and "The Loop" macro-projects are to be climate-controlled, vegetated enclosures whilst the "Magic Carpet" may become an electricity-desalination mainstay of the future basic infrastructure of every Gulf ecosystem-state. 1 Nomenclature: E electrical energy provided by the whole PV array, kWh global heat transfer coefficient from the photovoltaic cell to the environment medium through the glass cover, W/(m 2 K) daily solar global irradiation, kWh/m 2 I solar global irradiance, W/m 2 P daily electrical PV energy per unit surface area, kWh/m 2 temperature, °C global heat transfer coefficient of the PV module, W/(m 2 K) heat transfer coefficient from the photovoltaic cell to the environment through the Tedlar layer Subscripts c solar cell g glass m solar module med medium/mean ref reference T Tedlar Greek letters absorptance packing factor PV cell efficiency transmittance
... The manifestation of land desertification in aeolian environments (Helldén, 1991) mainly induces surface morphological changes caused by sand drifts (Zhenda et al., 1984). The complex nature of this process renders such changes difficult to quantify, and a quantitative assessment of aeolian desertification processes is required to allow the development of aeolian desertification prevention and control strategies (Canora et al., 2015). ...
Aeolian desertification is a severe ecological and environmental problem in arid regions. Research on its spatio‐temporal distribution, modelling, and driving force is necessary to prevent the development of aeolian desertification. In this study, the Moltsog dune field in Mongolia and the Ujimqin dune field in China were selected as the study areas, as both contain dunes under similar physical conditions. Using Landsat data from 1988, 1995, 2002, 2009, 2016, and 2020, the spatial‐temporal distribution and the degree of development of aeolian desertification in the two dune fields over the past 30 years were compared. Two periods of high‐resolution images were then used to compare the surface morphological changes induced by aeolian desertification in these dune fields. Climatic and socio‐economic data of the same period were used to compare and analyse the potential causes of changes in aeolian desertification in these regions. The results show that: (1) Over the last 30 years, the degree and development rate of aeolian desertification in the Ujimqin dune field were generally higher than those in the Moltsog dune field, and the former had a high degree of fragmented aeolian desertification patches with an expanding range. (2) The main form of aeolian desertification is reactivation of fixed dunes, which includes the development of blowouts on the flat grassland under the influence of human activities in the Ujimqin dune field. (3) Desertification in Moltsog is mainly affected by climatic factors, while that in Ujimqin is mainly driven by anthropogenic activities. The latter is specifically affected by the high grazing intensity before 2000 and increased mining activities after 2000. These findings provide a reference for comparing the aeolian desertification process and meaningful information for preventing and controlling aeolian desertification and enabling the sustainable development of dune fields in arid regions. This article is protected by copyright. All rights reserved.
... In fact, our results can help to explain abrupt changes in dryland ecosystems in the past. For example, we could explain why rapid desertification that occurred in the Sahel in the 1970s [a zone with aridity values around 0.8, whose drought in the 70s actually gave birth to the term of desertification, (32)] recovered so fast after wet years during the 1980s (33). Evidently, we cannot conclude that crossing aridity values of 0.8 a given year would lead to abrupt shifts in productivity, which should be studied by examining the relationship between dynamical changes in aridity and productivity taking into account both how strong is the change in aridity and its duration. ...
The constant provision of plant productivity is integral to supporting the liability of ecosystems and human wellbeing in global drylands. Drylands are paradigmatic examples of systems prone to experiencing abrupt changes in their functioning. Indeed, space-for-time substitution approaches suggest that abrupt changes in plant productivity are widespread, but this evidence is less clear using observational time series or experimental data at a large scale. Studying the prevalence and, most importantly, the unknown drivers of abrupt (rather than gradual) dynamical patterns in drylands may help to unveil hotspots of current and future dynamical instabilities in drylands. Using a 20-y global satellite-derived temporal assessment of dryland Normalized Difference Vegetation Index (NDVI), we show that 50% of all dryland ecosystems exhibiting gains or losses of NDVI are characterized by abrupt positive/negative temporal dynamics. We further show that abrupt changes are more common among negative than positive NDVI trends and can be found in global regions suffering recent droughts, particularly around critical aridity thresholds. Positive abrupt dynamics are found most in ecosystems with low seasonal variability or high aridity. Our work unveils the high importance of climate variability on triggering abrupt shifts in vegetation and it provides missing evidence of increasing abruptness in systems intensively managed by humans, with low soil organic carbon contents, or around specific aridity thresholds. These results highlight that abrupt changes in dryland dynamics are very common, especially for productivity losses, pinpoint global hotspots of dryland vulnerability, and identify drivers that could be targeted for effective dryland management.
... The amount and distribution of rainfall plays an important role in the environmental and the economic aspects of the country especially pastoralism and rain fed agriculture (MOIWR, 1999;Adam, 2000). In this respect studies based on remotely sensed data showed that the vegetative cover expands and contracts significantly following the erratic nature of the rain fall (Hellden, 1991;Giannini et al., 2003). According to Abdalla et al., (2011) the average annual discharges of the River Nile and its tributaries are as follows: The River Nile 83billion cubic meters (bcm) (at Aswan) Blue Nile 50.7 bcm White Nile 27.8 bcm (at Malakal) Bahr El Jebel 26 bcm (at Mongalla) Dindir River 3 bcm Rahad 1.09 bcm Atbara 12 bcm (7 bcm from setit and 5 bcm from Atbara) ...
Although Africa’s share to the causes of Climate Change is insignificant yet, the continent is the most vulnerable to the impacts of the phenomenon. The Nile Basin witnesses very high population growth rates, severe impacts of climate variability and change and severe food insecurity. About 94% of the Sudan is located in the arid and semiarid regions. Desertification, climate change and other forms of environmental degradation strongly contribute to poverty, displacement and conflicts. Separation of south Sudan imposed huge economic hardships to the country which was formerly reported to achieve economic stability due to the implementation of the Comprehensive Peace Agreement. Recent projections showed that the Sudan will witness severe water shortages of about 30 billion cubic meters by the year 2027. Different factors like the ENSO Event were found to contribute to the variability of the country’s rain fall and consequently, severe droughts, devastating floods and substantial socioeconomic impacts were incurred. Due to Climate Change the rain fall of the country showed 19% reduction and increased variability. Meanwhile, further reduction in rain fall coupled with south ward shift of agro-climatic zones and reduced crop productivity were anticipated. Climate resilience is maintained by creating conducive policy environment, strengthening relevant institutions and early warning systems and implementation of the relevant programs and projects. In addition to that basin (regional) cooperation is of vital importance especially promotion of regional trade, coordinated reservoir operation and joint research. The Higher Council for Civil Defense is the apex body to coordinate disaster management in the Sudan. The paper recommends that the efforts to craft the national water policy, other sectoral policies, the national IWRM plan and the NAP are to be urged.
... This study used Normalize Difference Vegetation Index (NDVI) measurements obtained from the National Oceanic and Atmospheric Administration Advance Very High-Resolution Radiometer (NOAA/AVHRR) and its relationship with rainfall gradients to analyse the vegetation production to determine desertification presence and associated risk to the deep well areas in the Senegalese side of the Sahel (Hanan et al., 1991). Hellden in the same year conducted a study in the Sudan side of the Sahel region to analyse NDVI trends, obtained also from NOAA/AVHRR, from 1981 to 1987 and compare his results with other research and results on the same area They established the need of a scientific based assessment of desertification, given on the lack of field data in the area and of the topic itself (Helldén, 1991). ...
The study and assessment of desertification and/or the advance or retreat of arid areas as a function of natural and anthropogenic causes is necessary for the prediction of future risks from climate change, and to support policymaking, action plans, and mitigation measures that can be taken at local and global scales. Remote sensing enables modelling, monitoring, and prediction of the behaviour of several elements of desertification. There have been numerous approaches to study desertification using remote sensing over the years. This research explored the timeline and global distribution of studies using remote sensing in studying desertification. Additionally, the review evaluated the key methods and variables that have been used to study desertification from remote sensing data.
The use of remote sensing for desertification studies can be trace back to 1991. From 2015 to 2020, more than 40 articles were published per year, showing that there has been a recent increase in the use of remote sensing techniques and its availability for monitoring desertification. Most regions of the world affected by desertification are being studied using remote sensing, however, there is a marked geographical variation between the number of studies in various regions, with Asia having disproportionately high number of studies compared to America or Africa. The country with most studies of desertification using remote sensing is China.
In terms of satellite data, Landsat images provide the bulk of data used to study desertification, especially the Thematic Mapper (TM) sensor. Classification and change detection are the most used methods to study desertification from remote sensing data. Additionally, land cover/land use change and vegetation and its attributes (e.g., Normalized Difference Vegetation Index - NDVI) are the most used variables to study desertification using remote sensing techniques. Finally, the review found major differences in terms of the ranges or thresholds applied to these variables when determining the presence or risk of desertification. Therefore, there is a need to develop thresholds and ranges of changes of key selected variables, which can be used to determine the presence of desertification.
... Rhodes 1991 "Desertification, as well as land degradation, has different meanings for different people and a variety of definitions and concepts of desertification and land degradation exist." Helldén 1991 "But no satisfactory evaluation system (exists due to several factors, including) multiple definitions of the desertification concept, …." Rubio and Bochet 1998 "Desertification … (is) difficult to precisely define… " Mainguet and Da Silva 1998 2000s "This plethora of definitions might give the impression that (desertification) is well-understood, but that is a myth. In reality, it hides a lack of knowledge of what it is. ...
Since its origins, the concept of desertification has been shrouded in controversy and ambiguity. As a result, no single definition of the term has been acceptable; there is no agreement on its extent or seriousness; and the solutions proposed are often disparate and counterproductive. This essay suggests all of this is due to the concept of desertification being a permanent ‘prisoner of history’, a historical process led by the United Nations Convention on Desertification (UNCCD). In this essay, I describe why the prisoner of history narrative applies to the concept of desertification. To do this, I review the historical events that built a metaphorical prison for desertification; show why definitions of the term ‘desertification’ are products of this prison; describe how so much misunderstanding and confusion in this field has led to real, negative consequences; and lastly, provide recommendations to young scientists as to how to avoid becoming incarcerated in this prison.
... Desertification is defined as land degradation in the drylands (Helldén, 1991) such as the Jordanian Badia. It is characterised by a loss of biological productivity and is broadly caused by a loss of soil nutrients (Veron et al., 2006). ...
Arid regions cover around one third of the Earth’s land surface, including 80% of Jordan. These regions may be suitable for the storage of carbon in their soils, providing environmental and economic benefits. This study was conducted to quantify the potential for soil carbon sequestration in dryland micro-rainwater harvesting (Vallerani) structures. The effect of changing climatic and land management conditions was investigated at the International Centre for Agricultural Research (ICARDA) field site in Al Majidiyya, Jordan. Field data was combined with modelling of carbon stocks using RothC-26.3 to meet this aim. Upscaling of the results and consideration of resultant ecosystem services was completed using the inVEST modelling tools. Results suggest that implementing Vallerani structures can lead to an increase in carbon stocks of 1.75 t/ha at the structure ridge and 4.26 t/ha in the structure furrow over a ten-year period. Upscaling these results shows a sequestration potential of 7.9 ± 0.76 t C at the study site, and almost 3 million tons across the Badia as a whole. Ecosystem service modelling demonstrates a potential economic cost of this sequestration to Jordan of as little as $17/ha, covering a large proportion of the implementation costs, even before benefits from increased food production, habitat improvement and other ecosystem services are considered. These results demonstrate that dryland water harvesting offers the potential for significant carbon sequestration compared to natural conditions. Further work should focus on constraining the economic costs and benefits to further expanding the water harvesting structures, as well as the impact of climate change on these predictions.
... Despite the fact that methods for large scale degradation/desertification assessments are widely employed and well developed, however, monitoring at appropriate spatial and temporal scales and with adequate remote sensing methodologies is still uncommon. This problem is well documented in numerous publications discussing the severity of land degradation/desertification impacts from regional to global scale (e.g., [8][9][10][11]). Accordingly, impact assessments, of land degradation and desertification necessitate a thorough quantification of indicators in the context of global change research, as these processes inherently feedback into the integral development of global economy [7]. ...
Remote sensing and thematic data were used to provide comprehensive views of surface conditions related to land degradation and desertification, considered environmental extremes in arid and semi-arid regions. The current work applies techniques, starting with simple visual analyses up to a parametric methodology, adopted from the FAO/UNEP and UNESCO provisional methodology for assessment and mapping of soil degradation. Egyptian case studies are highlighted to insinuate on studied aspects. Variable satellite imageries (MSS, TM, and ETM) and aerial photographs were utilized to provide data on soil conditions, land cover, and land use. IDRISI and ArcGIS software were used to manage thematic data, while ERDAS IMAGIN was used to process satellite data and to derive the normalized difference vegetation index (NDVI) values. A GIS model was established to modify the universal soil loss equation (USLE) calculating the present state and risk of soil degradation. The study area is found exposed to slight hazard of water erosion, however, and to high risk of wind erosion. It is also threatened by a slight to high salinization and slight to moderate physical degradation. It is recommended to use a GIS in detailed and very detailed studies for evaluating soil potentiality in agricultural expansion areas.
... La desertificación, fue descripta en la década de los 70, como la expansión de las condiciones de desierto en áreas áridas o semiáridas debido a la influencia del ser humano o del cambio climático (Rapp, 1974;Helldén, 1991), también se la definió como la disminución o destrucción de la actividad biológica potencial de las tierras, provocando en última instancia condiciones de desierto (UNCOD A/CONF, 1977), o como un proceso de empobrecimiento de ecosistemas áridos, semiáridos y algunos subhúmedos por los impactos combinados de las actividades humanas y las sequías (Dregne, 1976). Se diferencia del término desertización, en tanto que desertificación refiere a los procesos que involucran un mal uso de sistemas secos, y desertización sólo para procesos naturales de aridización del clima (Abraham, 2003). ...
In this thesis, different aspects of Puna pastoral systems were analysed, based on natural vegetation and its relationship with traditional livestock management. Data were collected in Santa Catalina, Jujuy province, taking into account seasonality in precipitation regimes. Vegetation units were mapped through georreferenced sampling units and satellite products, as vegetation indexes and band combinations. Each vegetation unit identified was described through its plant cover, aerial biomass and species composition, evaluating separately the two strata present in Puna vegetation, high and low. High stratum species were also measured (height, maximum and perpendicular diameter) in order to develop predictive equation of the plant biomass by species and life form. A carrying capacity model was developed specifically for this region, taking into account its environmental characteristics and based on the ecological theory of predator-prey interaction. Results showed that vegetation is influenced by climate (mainly precipitations) and geomorphology. The most productive vegetation units, considering aboveground primary production and carrying capacity, were chillaguales, vega and peladares. These units had also the higher animal stock (sheep and llamas) and wild herbivores (vicuñas), although the presence of vicuñas was influenced by human activities.
In the study area a varied group of pastoral systems were analyzed: local producers cooperative (COOPASAC), an indigenous community and private producers. Livestock management did not show differences among productive units, being the most relevant problems for the activity the reduced forage and water availability for animals during dry periods. These problems were severe in the last year, due the small amount of precipitation in the wet season, causing a management oriented to reduce stock numbers.
Diverse evidences of land degradation were found, especially symptoms of water and wind erosion at some vegetation units, associated, in part, to a heterogeneous livestock habitat use. The results obtained contribute to the knowledge of a region scarcely studied from a plant-herbivore interaction perspective, and how it is influenced by local pastoral activity. Based on the information obtained, future studies at a higher time and space scale, are needed to develop adequate animal stock in the area, preventing land degradation processes.
... Desertification conditions are to a certain extend man-made. They are caused by one or a combination of the following: transient (patchy) tillage (agriculture), over-grazing, lumbering and deforestation of perennials; drought, agriculture mismanagement practices, fire, Aeolian sand deposition and dune formation; soil erosion, water logging and soil salinization (Helldén 1991). ...
This chapter analyzes, generally, the problems of desertification and land degradation, highlighting the difference between the two terms and aspects to be assessed. The common land degradation/desertification processes, in Egypt will be highlighted, however the current chapter, as a start of an articles series focusing on desertification, will only consider three important processes (i.e. urban encroachment, salinization and wind erosion) to be detailed studied. Both the descriptive and quantitative approaches will be followed and merged, showing advantages of combining both approaches in assessment, sizing and combating preparedness. Regional assessment scale for the whole territory of Egypt, in addition to some detailed case studies will be introduced, with adaptation of indicators scale. Remote sensing, in addition to thematic maps, may supply valuable information concerning landscape features, vegetation type and quality and land use/cover, as inputs of the FAO-UNEP provisional methodology to assess aspects of different desertification processes. Multi scale and multi spectral satellite sensors supply reliable data sources to point out variable indicators needed to evaluate the present status and risk of different degradation/desertification processes. Multi temporal satellite imageries and thematic data make it possible to detect temporal land use/cover changes, hence compute the annual rate of a desertification process. The EU-MEDLUS methodology assessing the environmental sensitivity to desertification is rather due to the use of remote sensing data in computing the Soil Quality Index (SQI), Vegetation Quality Index (VQI), and Management Quality Index (MQI). Climate Quality Index (CQI) may be computed, using meteorology satellites data. The Geographic Information System (GIS) is a valuable tool to store, retrieve, update and manipulate the huge amount of data needed to map aspects if each desertification process. The system also facilitates computation and mapping environmental parameters of different quality indices, hence determining Desertification Sensitivity Areas (DSA’s). The Egyptian territory is susceptible to very high-to-high desertification sensitivity. However the Nile Valley is moderately sensitive due to cultivated vegetation cover. Combating desertification measures are essential for the sustainable agriculture. Special concerns have to taken at the desert oases, wadis and interference zone due to their rule in decreasing food gaps and accelerating agriculture expansion. Operational innovative monitoring is recommended to an early control of desertification sensitivity. Defining and followup the Environmentally Sensitive Areas (ESA’s) are needed to point out the risk, magnitude and causes of land degradation and desertification processes. Combining both descriptive and quantitative desertification approaches may grantee full sizing of desertification impacts.
... A few decades later, with the droughts in the Sahel in the 1970s and 80s, desertification became known as an environmental issue of global concern, which gradually achieved a worldwide iconic status. Although comparisons of aerial photos and satellite images over time soon came to undermine this idea (Helldén, 1991;Tucker, Dregne, & Newcomb, 1991) demonstrating in contrast that most of the Sahel was 'greening' mainly due to increased rainfall (Dardel et al., 2014;Hutchinson, Herrmann, Maukonen, & Weber, 2005;Olsson, Eklundh, & Ardö, 2005), desertification has continued to live on as an institutionalised fact in the UN system, among international aid donors and African governments (Benjaminsen & Hiernaux, 2019;Davis, 2016). Figure 2. Forest landscapes of the past (above) and present (below) as a result of human-induced degradation in West Africa, according to Aubréville (1949). ...
Visual representations remain under-studied in environmental discourse analysis. Drawing on Barthes’ notions of denotation, connotation and myth in visual communication, I provide three examples of images of landscape degradation, which are responsible for spawning degradation myths: cracked soil demonstrating desertification in the West African Sahel, fence-line contrasts showing degradation of communal rangelands in South Africa, and colour maps as evidence of overstocking in Sámi reindeer husbandry in Norway. In all three cases, degradation images are used to uphold a myth about pastoral mismanagement of the environment. The cases also reveal the use of images as powerful tools to ‘problematise’ pastoralism, whereas technical measures, such as implementing carrying capacities, are presented as solutions, despite scientific evidence questioning the idea of general overstocking. In addition, we see that connotative meanings of images have been pivotal in all the cases producing the myths on which policymakers have tended to base their decisions.
... A result of such fluctuation could be alteration in ecosystem function . Variation in climate is a major driver of environmental change in the dry land which could lead to a naturally occurring phenomenon as desertification (Adamu & Dejenie, 2013;Hellden, 1991). For example, an increase in annual average temperature and a decrease in annual average rainfall of about 1.1°C and 81 mm respectively were reported in Borno and Adamawa States which has resulted in the drying up of water sources and poor vegetation growth, leading to observed desertification (Onyeanusi & Otegbeye, 2012). ...
Northern Nigeria is faced with the global environmental problem of desertification. With the rate of desert encroachment of about 0.6 – 0.7Km per annum and 63.83% of the total area being impacted upon. Climatic factors such as increased annual average temperature and decreased annual average rainfall are the causes of desertification. Other causes are anthropogenic factors such as deforestation, cultivation on marginal land and overgrazing. Desertification as impacted negatively on biodiversity including health and livelihood. Over the years there have been government interventions aimed at combating desertification. Despite these efforts, the problem still persists due to inconsistent, poor implementation and management of these interventions. This paper discussed the challenges in tackling the problem of desertification such as over dependency and erratic nature of afforestation projects including improper planning of irrigation projects. Also discussed are possible solutions in mitigating the problem and how Nigeria can localize the Chinese model of desertification control. Such models as mechanical and biological measures have been practically implemented in various desert prone areas in China. Also, such recommendations and the Chinese model will assist in promoting mitigations and fighting against desert encroachment in northern Nigeria.
KEYWORDS: Desertification, northern Nigeria, Dry-land ecosystem, Chinese model, livelihood
... Using vegetation indicators-such as biomass, coverage, or productivity-as diagnostic indicators of the health status of grassland ecosystems may result in the mistaking of natural vegetation growth for dynamic and grassland degradation, thereby complicating the process of soil degradation monitoring. In view of this, some studies have regarded the recuperability after a drought [47,48] or precipitation utilization [49,50] as land degradation diagnostic indicators. However, these indicators only consider precipitation, which is suitable for hot arid and semi-arid areas because of its absolute effect on vegetation growth. ...
In this study, we proposed climate use efficiency (CUE), a new index in monitoring grassland ecosystem function, to mitigate the disturbance of climate fluctuation. A comprehensive evaluation index (EI), combining with actual vegetation net primary productivity (NPP), CUE, vegetation coverage, and surface bareness, was constructed for the dynamic remote sensing monitoring of grassland degradation/restoration on a regional scale. By using this index, the grassland degradation/restoration in the Three-River Source Region (TRSR) was quantitatively evaluated during 2001–2016, which has been an important ecological barrier area in China. Results showed the following: During the study period, the grassland of Yellow River source (SRYe) had high vegetation coverage, NPP, CUE, and low bareness, whereas Yangtze River source (SRYa) had low vegetation coverage, NPP, CUE, and high bareness. The vegetation coverage and CUE of the grassland showed upward trends, with annual change rates of 0.75% and 0.45% year −1. The surface bareness and NPP showed downward trends, with annual change rates of −0.37% year−1 and −0.24 g C m−2 yr−2, respectively. Assessment of EI revealed that 67.18% of the grassland of TRSR showed a recovery trend during the study period. The overall restoration of the SRYe was the best, followed by SRYa. However, the status of Lancang River source (SRLa) was poor.
... This view of grazing induced degradation in the Sahel has since been questioned: First, the very concept of desertification has been criticized (Behnke & Mortimore, 2016;Helldén, 1991;Hiernaux, Dardel, Kergoat, & Mougin, 2016;Rasmussen, 1999;Rasmussen et al., 2016). Second, it has been shown, at the scale of the entire Sahel, that most of the variation in grazing land production (one of the measurable indicators of 'land degradation') during and after the Sahel droughts in the 1970s and 1980s could be explained by rainfall variations (Fensholt et al., 2012;Fensholt et al., 2013;Huber, Fensholt, & Rasmussen, 2011). ...
It has been widely asserted that a high grazing pressure has led to a reduction in vegetation production at decadal time scales, implying land degradation, in African drylands, and in the Sahel in particular. We test this hypothesis by analyzing spatio‐temporal patterns of vegetation production in the north‐western Ferlo in Senegal. Normalized Difference Vegetation Index (NDVI) patterns, here used to represent vegetation production, were determined on the basis of Earth observation MODIS and PROBA‐V data. Furthermore, woody cover was assessed by very high spatial resolution (VHR) imagery. Since livestock is concentrated around deep wells in the dry season for watering, while for management they concentrate daily around pastoral family settlements or camps all year round, we studied the dependence of NDVI on distance from deep wells and camps. Locations of wells and camps were determined by visual inspection of VHR images. We found that ‘inverse grazing gradients’, defined as decreasing NDVI/production with increasing distance, dominated both around wells and camps. Further we found neither decrease nor increase in woody cover with distance to wells. Both positive and negative trends in wet season NDVI over the period 2000‐2016 were identified within the study area, yet temporal trends were predominantly positive in proximity to deep wells. Around pastoral camps, positive NDVI trends were generally elevated relative to the regional average. The results question the validity of claims that high grazing pressure causes land degradation at the landscape scale, yet they show that grazing does lead to substantial spatial redistribution of vegetation production
... The first drought period in the past century lasted from 1909-1915 ( Nicholson, 2012) but the early researchers neglected the fact that the data for such a short time span would rather indicate only climatic fluctuations instead of real climatic crisis ( Mainguet, 1991). A new paradigm regarding desertification emerged at the beginning of the 1990s: the "re-greening Sahel" ( Helldén, 1991;Thomas and Middleton, 1994;Nicholson et al., 1998;Mainguet, 1999;Herrmann and Hutchinson, 2005;Olsson et al., 2005;Helldén and Tottrup, 2008;Knauer et al., 2014;Behnke and Mortimore, 2016). This new paradigm is predominantly based on studies using coarse satellite remote sensing data (NOAA-AVHRR) monitoring the period from 1981 until today ( Anyamba and Tucker, 2005;Nicholson et al., 2012;Dardel et al., 2014b). ...
Since the turn of the millennium various scientific publications have been discussing a re-greening of the Sahel after the 1980s drought mainly based on coarse-resolution satellite data. However, the author's own field studies suggest that the situation is far more complex and that both paradigms, the “encroaching Sahara” and the “re-greening Sahel”, need to be questioned.
This paper discusses the concepts of desertification, resilience, and re-greening by addressing four main aspects: (i) the relevance of edaphic factors for a vegetation re-greening, (ii-iii) the importance of the selected observation period in the debate on Sahel greening or browning, and (iv) modifications in the vegetation pattern as possible indicators of ecosystem changes (shift from originally diffuse to contracted vegetation patterns).
The data referred to in this paper cover a time period of more than 150 years and include the author's own research results from the early 1980s until today. A special emphasis, apart from fieldwork data and remote sensing data, is laid on the historical documents.
The key findings summarised at the end show the following: (i) vegetation recovery predominantly depends on soil types; (ii) when discussing Sahel greening vs. Sahel browning, the majority of research papers only focus on post-drought conditions. Taking pre-drought conditions (before the 1980s) into account, however, is essential to fully understand the situation. Botanical investigations and remote-sensing-based time series clearly show a substantial decline in woody species diversity and cover density compared to pre-drought conditions; iii) the self-organised patchiness of vegetation is considered to be an important indicator of ecosystem changes.
... Mainly, several studies have shown the importance of remotely sensed data to quantify desertification change at a large scale for long and short time period. The majority of these studies have been focused on green mass (vegetation) [3][4][5]. Furthermore, where the sand presents a high spectral reflectance than vegetation in the desert areas (Figure 1), other studies have been concentrated on this material to quantify and track sand dunes encroachment variability with time in order to assess and track desertification [6][7][8]. ...
The purpose of the present work is to assess desertification change in the Tarfaya basin (Morocco) based on quantifying sand dunes mass change at the corridor scale using two Panchromatic bands of Landsat ETM+ and OLI with 15 m of resolution covering the study area for ten years (2005–2016). In this work, the sand dunes quantification is qualitative and is based on automatic extraction and classification of sand dunes shape using co-occurence texture filters and Support Vector Machine (SVM) classifier. The statistical results show that the area covered by sand was increased during the last ten years, which reveal that desertification becomes more intense.
... 10 (Helldén, 1991;Thomas and Middleton, 1994;Nicholson et al., 1998;Mainguet, 1999;Herrmann and Hutchinson, 2005;Olsson et al., 2005;Helldén and Tottrup, 2008;Knauer et al., 2014) .This new paradigm is predominantly based on studies using coarse satellite remote sensing data (National Oceanic and Atmospheric Administration -Advanced Very High Resolution Radiometer -NOAA-AVHRR), monitoring the period 1981 until today Nicholson et al., 2012;Dardel et al., 2014b). Since the millennium 15 additional data like MODIS and SPOT Vegetation (VGT) NDVI data have been used (e.g. ...
Since the turn of the millennium various publications have been discussinga re-greening of the Sahel after the 1980's drought mainly based on coarse-resolution satellite data. Recent field studies show a more differentiated picture questioning both paradigms, the Encroaching Sahara and the Re -greening Sahel.
The author set out this article to discuss the concepts of Desertification, Resilience and Re-greening by addressing three main aspects: (i) relevance of edaphic factors for a vegetation re-greening, (ii) importance of the selected observation period in the debate of Sahel greening or browning, and (iii) modifications in vegetation pattern as possible indicators for ecosystem changes (shift from originally diffuse to contracted vegetation patterns).
The data used in this article cover a period of more than 150 years and include the author's own research results from the early 1980s until today. A special emphasis, apart from field work and remote sensing, is laid on the analysis of historical documents.
The key findings summarised at the end show the following: (i) a vegetation recovery predominantly depends on soil types; (ii) when discussing Sahel greening vs. browning, the majority of research articles only focuses on post-drought conditions. However, if pre-drought conditions (before 1980s) are analysed, remote sensing based time series and botanical investigations clearly show a substantial decline in diversity of woody species and cover density, compared to pre-drought conditions; (iii) self-organised patchiness of vegetation is considered to be an important indicator for ecosystem changes.
... In the 1990s, the desertification paradigm was questioned (e.g. Hellden, 1991;Nicholson, Tucker, & Ba, 1998;Thomas, 1993) and finally replaced by a new paradigm, the greening Sahel (e.g. Dardel et al., 2014;Fensholt et al., 2012;Hutchinson, Herrmann, Maukonen, & Weber, 2005). ...
In recent years, many regions in sub-Saharan Africa have experienced growing contestations of existing livelihood practices and massive environmental change. This has been accompanied by what has sometimes been described as a ‘respacing’ of Africa, i.e. an increasing blurriness of the nation state and social relationships becoming more and more interconnected on the local to global scales, rendering conventional concepts of space and territory obsolete. In this introductory essay, we briefly discuss notions of this ‘respacing’ process, highlight its validity but also its ambiguity, and thus lay the ground for the ensuing compilation of papers on social, environmental, and spatial change in sub-Saharan Africa.
... Overgrazing, fuelwood cutting and cultivation pressure brought intense processes of environmental degradation to nearly all of the rangelands in Saudi Arabia (Heady, 1963;Batanouny, 1991;Al-Rowaily, 2003;Chaudhary, 2010;Dregne, 2002;El-Keblawy et al., 2009). Increased human activity tends to over-stress land and vegetation which has increased steadily across the entire Arabian Peninsula leading to resources degradation, salinization, and erosion (Kingery, 1971;Khan, 1982;Hellden, 1991;Oatham et al., 1995;Ghazanfar, 2003;Kharbotly et al., 2003;Geist and Lambin, 2004). The result has been a drastic reduction of species diversity, density, composition and reduction of plant cover (Barth, 1999;Al-Rowaily, 1999). ...
Saudi Arabia rangeland ecosystems have undergone intense processes of degradation for many decades because of extreme climate and human activities such as overgrazing and socioeconomic changes. In this study, Hail and Qassim Regions of Saudi Arabia covering an area about 79610.73 km² were selected to study the rangeland vegetation and condition. Haloxylon salicornicum was the most dominant species, covering more than 56% of the total area. The second prominent community was Acacia-Lycium shawii, which covers about 21% of total area. It was found that about 65% of vegetation in the surveyed area is in good or very good condition compared with about 31% in poor or deteriorated condition. Effective measures such as determination of carrying capacities and development of grazing systems have to be implemented to ensure resources sustainably.
... Attributing this present state of apparent degradation to anthropogenic factors, such as overexploitation of natural resources by mobile pastoralists, is too short-sighted. For example, there was great alarm over land degradation after the great Sahel droughts of the 1980s, but evidence showed that the vegetation re-established itself in pastoral areas in subsequent years (17). The areas where grassland recovery was most significant were found in the northern Sahel, where grazing dominates over cropping. ...
This paper argues that pastoral commons are under increasing pressure not just from overuse by pastoralists themselves, but from land management policies. Since colonial times, these have been based on a persistent misconception of the nature of pastoral economies and combined with increasing land alienation and fragmentation through government policies and covert privatisation of pastures. The paper focuses especially on pastoral populations in African drylands and is based on long-term research by independent researchers summarising some of their experiences in western, eastern and southern Africa. Most of them are organised in the African Drylands Dialogue, trying to shed some light on the developments in these areas. Before discussing the actual situation of African pastoralists, the authors focus on basic institutional features of the political and economic management of common grazing lands. This is followed by an overview of land alienation processes in colonial times, which serves as a basis for understanding the current land alienation constellations. The paper then moves on to explain how and why pastoralists are framed by the national discourses as the 'other' and the 'troublemaker', even being labelled as terrorists in nation state contexts. This goes hand in hand with a new wave of land alienation in the form of large-scale land acquisitions or 'land grabbing' (including water grabbing and 'green grabbing' processes). The paper then outlines different coping and adaptation strategies adopted by pastoral groups in a context in which a range of different global and local political, economic and ecological situations interrelate ('glocal'). Finally, the paper discusses the way in which pastoralism could be reframed in a participatory way in the future.
... Firstly, already in the early 1990s, Helldén (1991) claimed that there was a lack of data to substantiate the hypothesis of a human-induced trend towards desertification in the Sahel. The causes of land-cover change are complex, and the relationship between human activities and habitat degradation in the Sahel is uncertain. ...
The links between conservation and livelihood concerns remain much debated, and there is no agreement about the degree to which these concerns are linked, and how they should be tackled together. The main objectives of this study are to uncover the local values of birds, the environment and conservation for rural people in Burkina Faso’s Sahel region, and to increase insights into interventions that aim to achieve integrated (migrant bird) conservation and sustainable development objectives in this area. By focusing on issues like local perceptions, local participation, local institutional arrangements and the role of birds, this study adds new insights to the existing literature and knowledge. The study demonstrates that both birds and the environment are valued in many ways and are strongly linked with local livelihoods. At the same time, the study shows that serious environmental problems exist, and that both local livelihoods and birds are negatively impacted. This has created conservation incentives among the local population, which is a major contributing factor for conservation organizations seeking local motivation and participation to combat environmental issues. In fact, the study provides a strong argument for the need to increase local participation, and demonstrates several ways to do so.
... Despite the general awareness that desertification is a serious natural and human problem in the drylands, it is not so clear what actually causes this desertification (Helldén, 1991). It is usually not a single cause, but most often a combination of factors that may change over time and can vary spatially. ...
... The degradation process of these landscapes has been a matter of preoccupation for the inhabitants of such regions, but especially for the technical and scienti c community worldwide. Searching for a solution to this problem, the dryland degradation process studies have evolved each day into greater integration of remote sensing and the Geographical Information System (GIS) (Breininger et al. 1991, Hellden 1991, Price et al. 1992, Ringrose et al. 1997. ...
... The degradation process of these landscapes has been a matter of preoccupation for the inhabitants of such regions, but especially for the technical and scienti c community worldwide. Searching for a solution to this problem, the dryland degradation process studies have evolved each day into greater integration of remote sensing and the Geographical Information System (GIS) (Breininger et al. 1991, Hellden 1991, Price et al. 1992, Ringrose et al. 1997). A large number of change detection techniques has been developed to obtain operational monitoring since the advent of the orbital system (Lillestrand 1972). ...
In developing countries, both deforestation and forest degradation are of serious environmental concern due to various driving factors. This can be more difficult to manage due to the lack of quality data and the unavailability of appropriate mapping techniques. Based on remote sensing data, this study examined an integrated approach to improve the mapping capability of forest change monitoring for data deficient areas. The study is carried out integrating ground-based information with Landsat 5 TM, Landsat 8 OLI and TIRS in the Man River Basin, India. The findings of the current study suggest that the integrated approach enhances the ability of modeling to estimate deforestation and forest degradation associated with responsible drivers, especially in countries such as India where grassroots data are infrequent.
Patterning of vegetation in drylands is a consequence of localised feedback mechanisms. Such feedbacks also determine ecosystem resilience ‐ i.e. the ability to recover from perturbation. Hence the patterning of vegetation has been hypothesised to be an indicator of resilience, i.e. spots are less resilient than labyrinths. Previous studies have made this qualitative link and used models to quantitatively explore it, but few have quantitatively analysed available data to test the hypothesis. Here we provide methods for quantitatively monitoring the resilience of patterned vegetation, applied to 40 sites in the Sahel (a mix of previously identified and new ones). We show that an existing quantification of vegetation patterns in terms of a feature vector metric can effectively distinguish gaps, labyrinths, spots, and a novel category of spot‐labyrinths at their maximum extent, whereas NDVI does not. The feature vector pattern metric correlates with mean precipitation. We then explored two approaches to measuring resilience. First we treated the rainy season as a perturbation and examined the subsequent rate of decay of patterns and NDVI as possible measures of resilience. This showed faster decay rates ‐ conventionally interpreted as greater resilience ‐ associated with wetter, more vegetated sites. Second we detrended the seasonal cycle and examined temporal autocorrelation and variance of the residuals as possible measures of resilience. Autocorrelation and variance of our pattern metric increase with declining mean precipitation, consistent with loss of resilience. Thus, drier sites appear less resilient, but we find no significant correlation between the mean or maximum value of the pattern metric (and associated morphological pattern types) and either of our measures of resilience.
This book examines the technical, market, and policy innovations for unlocking sustainable investment in the energy sector. While finalizing this book, the COVID-19 pandemic is cutting a devastating swath through the global economy, causing the biggest fall in energy sector investment, exacerbating the global trade finance gap, worsening signs of growing income inequality, and devastating the health and livelihoods of millions. What is the parallel between the COVID-19 pandemic and the climate change crisis? The impacts of the global pandemic are expected to last for a few years, whereas those associated with the climate crisis will play out over several decades with potentially irreversible consequences. However, both show that the cost of inaction or delay in addressing the risks can lead to devastating outcomes or a greater probability of irreversible, catastrophic damages. In the context of sustainable energy investment and the transition to a low-carbon, climate-resilient economy, what ways can financial markets and institutions support net-zero-emission activities and the shift to a sustainable economy, including investment in energy efficiency, low-carbon and renewable energy technologies? This book provides students, policymakers, and energy investment professionals with the knowledge and theoretical tools necessary to address related questions in sustainable energy investment, risk management, and energy innovation agendas.
States tend to see mobile livestock production based on herding as unproductive, ecologically destructive and the cause of land-use conflicts. Governments therefore seek to actively control and govern pastures and pastoralists through quantifiable indicators often justified by ecological succession theory. But this theory has been challenged by alternative ideas about non-equilibrium ecosystems in many pastoral areas. This chapter presents examples from African drylands and reindeer husbandry in the Arctic that question top-down state governance and the views that it is based on. It also illustrates two central themes in political ecology—a deconstruction of the idea of widespread environmental degradation caused by smallholders, and an analysis of how these already marginalized producers are subject to further marginalization through persistent and flawed attempts to modernize their production.
Continuing the focus on conservation, this chapter introduces feminist political ecologies, which combine elements of feminist thinking and political ecology. Studies in countries in the Global South tend to reveal large gender inequalities in local governance on questions about conservation, and the chapter provides examples of such inequalities from Senegal, India and Nepal. In the Global North, however, many take it for granted that women have gained a high degree of equity in political representation in all fields. However, through studies of local representation in processes to extend protected areas, the chapter shows how rural Norwegian women have systematically been denied their legal rights of representation. The use of a ‘chain of explanations’ reveals how elements from different local and national levels together have caused this discrimination.
Desertification and its causes are dynamic processes, which therefore make it necessary to discuss the factors that drive desertification in a specific spatiotemporal sense. Here the temporal trends in potential evapotranspiration (PE) and precipitation were selected as climate change indicators, five possible scenarios were established and relationships between desertification and the climate change indicators were examined for different time periods across northern China. The results indicate that climate change was the primary or one of drivers of desertification reversion in the northeastern and northwestern regions of China between 1975 and.
1990, whereas the desertification reversion near Mu Us Desert was influenced primarily by human intervention. Climate change triggered desertification variation across the entire region, including the Hulenbur, Otigdag, Horqin, Horbq, and Mu Us deserts and the Sounite Grassland between 1990 and 2000. However, the desertification reversion near the Otindag, Mu Us and Horqin deserts was due primarily to human intervention. Desertification reversion occurred across 54,609 km² between 2000 and 2005 in northern China and climate change was thought to be related to majority reversion, whereas the regions that experienced desertification development and aggravation, including the areas near the Hulunbuir and Nengjiang deserts, were influenced primarily by human intervention. Broad desertification reversion occurred across the North China region between 2005 and 2010, with 45,787 km² experiencing desertification reversion compared with only 8026 km² experiencing desertification development and aggravation, however, climate change had a limited effect on desertification in this period. The study provides a new understanding of the causes of desertification, and an easier and more effective framework for determining the role of climate change on desertification.
In this chapter we show that the development of plant communities in time must be known if we want to understand their actual floristic and structural composition. The first section describes the development of plants during earlier geological times, where temporal vegetation dynamics were largely influenced by tectonic and climatic events. In particular, the worldwide periodic fluctuations between cold and warm periods in the Pleistocene led to strong vegetation changes and resulted in spatial separations of different vegetation types. Today, intended or unintended human influences on vegetation are becoming increasingly important, leading to changes in vegetation structure, composition and the loss of plant species, as well as to a growing number of invasive species. We exemplify these aspects by discussing anthropogenic influences on vegetation in more detail for the Mediterranean, Saharan and tropical environments. In the following section, we present general aspects of temporal vegetation dynamics, including primary succession and secondary succession following more or less natural or human-made disturbances. Examples are given for mosaic cycles, cohort dynamics and the carousel model. We discuss different plant strategy models, which can be related to successional dynamics (r and K, CSR, resource-ratio, facilitation-tolerance-inhibition). The final section deals with aspects of ecological stability and the influence of disturbances, introducing the concepts of resistance, resilience, robustness, variability and persistence of plant communities.
Following a 25 years of below average annual rainfall in Sahel during the 1970-1995 period , the return to more humid conditions led to a rapid post-droughts recovery of the woody cover. However, the increase of the woody cover is not spatially homogeneous raising questions about the resilience of some woody vegetation types. Based on the analysis of field and remote sensing data collected on the tiger bush systems in northern Mali, this study pointed out the current and persistent degradation of the tiger bush systems in Sahel since the 70s in spite of the recent improvement of rainfall since mid-1990s of rainfall and the general Sahel regreening. Following 25 years of below average rainfall amounts, profound changes in the woody population pattern, tree density and cover, and floristic composition took place regardless of the site location along the rainfall gradient. Associated to definite structural changes of the woody population, surface hydrologic processes converted from a sheet to concentrated run-off accelerating the collapse of the patterned woody population. Nowadays, there is no evidence in favour of a reversibility of the current degradation process at least at a decadal scale although a very sparse recolonization by a pioneer vegetation has been observed in the driest sites along recently formed gullies. These observations support the hypothesis of an ecosystem shift, with long term implications on structure and functioning of the ecosystem but also at the whole landscape scale through, for example, the increase of run-off leading to stronger water flows in enlarged wadis, aggravating soil erosion upstream and sediment deposition downstream, enhancing water storage in ponds and the recharge of aquifers.
Case studies on desertification in northern Burkina Faso, in the Western Sahel, using satellite-aided ground navigation technology, have shown that a noticeable environmental degradation took place from the late 1960s to 1990. Analyses of aerial photographs and satellite images indicate that the most severe land degradation occurred during the first of a series of droughts, which started in the late 1960s, when large areas with bare ground developed. Despite increased rainfall since 1985, the areas with bare ground have not recovered. The main cause is to be found in a combination of human impact and of repeated droughts.
IntroductionApproaches to desertification indicatorsGlobal and regional indicators of land degradation and desertificationApplying selected concepts in practiceDesertification, resilience and stabilityThe soil and water conservation and protection functionsSpatial variability and discontinuityHydrological indicators of desertificationWater in the soil and landscapeReferences and further reading
The nature of desertificationThe links between global and local desertificationDiscussion: desertification as a world-wide and historical phenomenonDiscussion: life and its feedback with the environmentDiscussion: the adaptation of people and cultures to desertificationDiscussion: Data and evidence for land degradationConclusion: why land degradation and desertification occurReferences and further reading
Drylands cover 40 % of the earth’s surface and provide the basis for the livelihoods of 2 billion people, many of whom belong to the poorest of the world. Dryland forests provide these people with woods, fruits, fibre and pasture. Drylands are among the poorest and most problem-ridden areas of the world. Therefore a different approach to drylands and dryland forest management is needed. The chapter develops a framework for analysing dryland forest management departing from a forestry approach to a landscape approach putting the diversity and interconnectedness of different forest and non-forest resources in the centre of analysis. It departs from the assumption that dryland ecosystems are not in equilibrium and extremely dynamic. Therefore, management should focus on forest ecosystems as providing a large diversity of resources niches in time and space for diverse groups of users, ranging from pastoralists to smallholders, men and women, indigenous peoples and caste. Rules of access and resource tenure should take account of this diversity.
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