Desertification Trends Research Articles

Sandy desertification trend in western Northeast China Plain in the past 10 years

The west sandy land of the Northeast China Plain is located in the eastern huge sandy belt of mid-latitude in Eurasia and the eastern fringe of desertified land with best bio-climatic conditions in China. With rapid economic development, the deterioration of eco-environment has occurred and the desertification becomes very obvious. The first part of this paper studies the regional differences of landscape patterns and explores the regional differences of desertification. The second part aims to reveal the dynamics of desertification in the 1990s by using NOAA/AVHRR data and thematic data in GIS database. This work lays a scientific basis for the rehabilitation and development of the sandy lands.

Assessment of the effectiveness of desertification rehabilitation measures in Yulin, north-western China using remote sensing

In China tremendous efforts have gone into the rehabilitation of desertified land for productive use such as grazing, crop cultivation and afforestation. In this study the effectiveness of these agro-ecological measures to combat desertification in Yulin, Shaanxi Province of north-western China, is evaluated from multi-temporal aerial photographs in a geographical information system (GIS). The trend of desertification between 1960 and 1987 is modelled from changes in other land covers. It is found that desertified areas have decreased by 717.91 ha during the study period as a result of rehabilitation efforts. Plantation of grass is the least effective measure for halting sand dune encroachment whereas the planting of shrubs is the most effective. The trend of desertification is most accurately modelled from the changes in grassland and farmland at an R 2 value of 0.90.

Application of NOAA-AVHRR NDVI time-series data to assess changes in Saudi Arabia's rangelands

The primary objective of this study was to assess the condition of a portion of Saudi Arabia's rangelands and evaluate the effects of grazing by the animal herds of indigenous nomads over the last decade. Because of the desertic condition of these rangelands, changes in vegetation cover are more subtle than would be the case for other, less arid areas. Consequently, a new analytic methodology for the detection of desertification of arid and hyper-arid rangelands was developed specifically for this project. The conceptual framework for the analysis is the use of the coefficient of variation (COV) of the monthly Normalized Difference Vegetation Index (NDVI, maximum-value composite) as a measure of vegetative biomass change. A higher NDVI COV for a given pixel (excluding cases of changes in land use) represents a greater change in vegetation biomass in the ground area represented by that pixel. Linear regression was used to determine the trend in COV values for each pixel over the 12-year period for which data was available; pixels with a negative slope are considered to represent ground areas with decreasing amounts of vegetation. Results were validated by tests of statistical significance and by comparison of the theoretical results to vegetation change and land-cover data from the remote sensing systems and from reconnaissance flights over select areas. These desertification trend results were then combined with land-cover information to provide an assessment of desertification status.

Irrigation expansion and dynamics of desertification in the Circum-Aral region of Central Asia

The aim of this paper is to examine the causes and dynamics of desertification in one of the world's worst disaster areas, the Aral Sea region. During the 1960s, a large-scale irrigation campaign aimed at achieving independence in cotton production was launched in Soviet Central Asia. From 1960, ever-increasing water withdrawal from the two inflowing rivers—the Amudarya and Syrdarya—has resulted in the dramatic decline of the level, area and volume of the sea. Desiccation was accompanied by the development and further acceleration of various desertification processes. The study reveals that, for different reasons, the predominant direction and trends of desertification have been changing during each of the four identified periods from 1961 to 1995. The main desertification processes recorded in the Circum-Aral region (‘Priaraliye’ in Russian) were a decline in the groundwater level, increased mineralization and chemical pollution of watercourses, soil salinization, the spread of xerophytic and halophytic vegetation, and deflation and aeolian accumulation, with the development of salt storms. Recent improvements in the situation are also discussed, along with their causes. Zonation of Priaraliye is carried out and an outlook for the future is given.

Desertification indicators as diagnosis criteria for desertification risk assessment in Europe

Despite the seriousness of the environmental and socio-economic impacts of desertification, few efforts have been made to devise diagnostic and monitoring techniques for appraising the status and trend of desertification. Indicators are integrated and synthetic information that can provide data on threshold levels, status and evolution of relevant physical, chemical, biological and anthropogenic processes. Existing studies have taken a global perspective, and most have dealt with rangeland conditions. Moreover, the zones usually studied have included countries whose socio-economic and cultural backgrounds differ from those prevailing in Europe. This paper presents a methodology and discussion of indicator requirements, selection and definition, procedures for measuring or making estimates, sensitivity, range of values and interactions. Emphasizing the need to use indicators to develop a system of desertification evaluation, this paper outlines the advantages and difficulties of using such an evaluation system.

Perspectives on desertification: south-western United States

Several climatic changes occurred in the northern Chihuahuan Desert and other parts of the south-west United States during the last 12,000 years leading to a markedly warmer and drier climate. Vegetation changed in response to this climatic shift. Generally, this transition was from coniferous woodland to grasslands and eventually to the present day desert scrub. Pre-Columbian inhabitants of this region adapted by changing from hunter-gatherer to primarily agrarian economics. European immigration into the south-west U.S. beginning in the mid 1500s greatly affected this region. The greatest impact occurred after the U.S. Civil War in the 1860s. Before that time land use tended to be localized near small agricultural areas, mines, and military installations. The post-war range livestock industry expanded dramatically, especially during the 1880s—a period of general abuse of arid lands in the region. Recognition of this abuse and the deteriorating productivity of the land led to greater government involvement, including establishment of experimental stations and eventually management of the public domain by governmental agencies. Fire suppression, mismanaged grazing, changing climatic conditions, loss of soil and increasing atmospheric CO2concentrations, mainly due to the burning of fossil fuels, are among the probable causes of continued desertification trends. Urban and rural populations, presently technologically isolated from their environment, need to better understand the dynamic nature of their environment. A greater degree of co-operation among diverse entities will be crucial.

The causes and developmental trend of desertification in the middle reaches of the Yarlung Zangbo River and its two tributaries in Xizang

The middle reaches of the Yarlung Zangbo River and its two tributaries are an important development and construction region in Xizang (Tibet) in recent years, but the fast development of desertification has caused immense damages to its social and economic development, so the study on desertification in this region is significant. The paper studies the causes and development trend of desertification in this region through analysis of natural and human factors as well as their relationship. It can be concluded that desertification in the study area is one process which is accelerated and intensified by human activities on the basis of the slow natural desertification process. It is resulted from the dislocation of irrational and intensive human activities, fragile eco-environment and meagre natural resources, and tends to become more wide and severe.

Satellite monitoring of desert plant community response to moisture availability

Our study demonstrates the utility of coarse spatial-resolution satellite spectra for analysis of vegetation phenophases and response to moisture availability in an arid ecosystem. We show the feasibility of deriving information on vegetation parameters such as stress and growth patterns in arid regions through the use of satellite-derived vegetation indices, despite the usual problems associated with a high ratio of soil to vegetation cover. Vegetation in our study area consists of Chihuahuan Desert grassland and scrub, including extensive zones of mixed desert scrub and grassland. Historic vegetation change has been well documented and is exemplified by decreasing grass cover and increasing shrub cover, a general trend of desertification. Our analysis suggests that satellite-based inputs can be used to improve our understanding of the spatial dynamics of climatic impacts on natural vegetation and to help us distinguish these processes from human-caused desertification.

Desertification in North China

Arid and semi-arid regions occupy nearly half the area of China, where there are abundant natural resources and a great potential for development. However, these regions have been seriously troubled by sandy desertification which has become an important restricting factor for local development. On the basis of research and practice over many years, we believe that sandy desertification is environmental degradation indicated by wind erosion resulting from excessive human activities. The degraded land is desertified land. Between the important human and natural contributing factors, the former is the more crucial. The evolution of sandy desertification depends on the process of wind erosion after the ecosystem has been destroyed by humans, and its indicator is mainly presented by wind-erosion landforms. Sandy desertification leads to a rapid decline in the biomass production and the potential productivity of land, and even loss of land resources. The trend of sandy desertification will depend fundamentally on the human impact in coming decades. A number of typical examples have proved that the desertified land can be restored to its potential productivity for agriculture and animal husbandry through different harnessing measures.

Precipitation trends, evapotranspiration and the ecological zones of Nigeria

An attempt is made to use the ratio⋋ of precipitation to potential evapotranspiration to qualify earlier climatic classifications of Nigeria for proper ecological zonation. Results show that in the pure forest belt located south of latitude 7° N the⋋ value is greater than 0.75, while in the middle belt (7–10° N) belonging to the wooded savanna and in areas further north gradually approaching steppe-type vegetation of pure Sahel, the values of⋋ below 0.40. Modulations of⋋ values (hence the eco-zones) appear to be responses to variable precipitation, especially in drought years. It is suggested that this notwithstanding, irreversible trends in land-surface degradation are mainly due to uncontrolled human interference in relation to large-scale agriculture in areas where⋋ is less than 0.40 in the Sudan-Shael belt of Nigeria. This needs to be re-appraised, if this desertification trend is to be checked

Desertification of Western Maharashtra: Causes and possible solutions. I. Comparative growth of eight tree species

In the low rainfall tract of Western Maharashtra, the degraded area that can be called a desert in the making is 2.28 million ha out of a total of 5.7 million ha or 40% of the area. The main causes of this desertification are overcultivation coupled with deforestation and overgrazing. The problem is made more acute by the increasing human and animal population, and the fact that rainfall is undependable and of high intensity. The trend of desertification can be reversed by (a) closing the area to grazing and uncontrolled wood cutting, (b) implementation of time-tested soil and water conservation measures and (c) large scale planting of suitable forage grasses and legumes as well as arid zone species of trees. The main research thrust of the trials with promising species of trees was to determine their suitability to wastelands and to investigate methods of establishing them rapidly and economically. Thus the effect of fertilization and spacing was examined for the following eight tree species: Acacia albida, A. nilotica var. cupressiformis, A. nilotica var. indica, Albizia lebbek, Cassia siamea, Dalbergia sissoo, Leucaena leucocephala, Melia azedarach and Prosopis juliflora. The two spacings used were 5 × 0.6 m and 3 × 1 m and the three fertilizer doses were 0:0:0, 50:50:50 and 100:100:100 kg N:P 2O 5:K 2O per ha. A factorial design with nine plant selections, three fertilizer treatments, two spacings and three replicates was used. A total of seven irrigations were applied from October 1983 to February 1984. At 15 months of age the average basal stem diameters of L. leucocephala and M. azedarach were significantly superior to all the other species. The average plant height of L. leucocephala, at 2.38 m, was superior to all other species. The use of fertilizer led to significant improvements in performance; however, there was little difference between using a dose of 50 kg ha −1 or 100 kg ha −1. An interaction was found to exist between the species and spacings. L. leucocephala and M. azedarach showed better performance at the spacing of 5 × 0.6 m and D. sissoo and P. juliflora performed better at 3 × 1 m. C. siamea at 62% had the lowest survival rate.

A New Global Assessment of the Status and Trends of Desertification

A reassessment of the status and trends of desertification was called for as part of a general assessment of progress in the implementation of the United Nations Plan of Action to Combat Desertification, seven years after the UN Conference on Desertification (UNCOD) in 1977. Because of the inadequate data existing at the country or state level, the basic generalization has been set at a wider regional scale. The new assessment has confirmed the global scale of the problem of desertification as presented to UNCOD, and has increased the area and populations considered to be at risk through its recognition of the threat of desertification in the sub-humid tropics. The threatened area of 4,500 million ha constitutes 35% of the land surface of the Earth, with almost 20% (850 millions) of the world's total human population. Estimates indicate that, of this area, 75% is already moderately desertified, and 30% is severely or very severely desertified.The rural population affected by severe desertification totals some 280 millions, or 470 millions if the urban component is included, with, respectively, 135 millions and 190 millions severely affected. These are significantly larger than the figures presented to UNCOD—mainly through the inclusion of additional sub-humid land in this assessment, but partly through national population increases and growth in the extent of severely desertified land. Both in terms of areas and population affected, the so-called developing regions are shown to be those worst-hit by desertification; and within these, the tropical semiarid and sub-humid lands tend to be the most ‘critical’ areas.

Population crisis and desertification in the Sudano-Sahelian region.

People living in the area just south of the Sahara Desert in Africa face their 3rd major drought since 1900. This drought brings about famine. Drought and famine are only manifestations of more profound problems: soil erosion and degradation. They diminish land productivity which aggravates the population's poverty. Yet soil erosion and degradation occur due to an expanding population. Continued pressures on the land and soil degradation results in desertification. The UN Environment Programme's Assessment of the Status and Trend of Desertification shows that between 1978-84 desertification spread. Expanding deserts now endanger 35% of the world's land and 20% of the population. In the thorn bush savanna zone, most people are subsistence farmers or herdsmen and rely on the soils, forests, and rangelands. Even though the mean population density in the Sahel is low, it is overpopulated since people concentrate in areas where water is available. These areas tend to be cities where near or total deforestation has already occurred. Between 1959-84, the population in the Sahel doubled so farmers have extended cultivation into marginal areas which are vulnerable to desertification. The livestock populations have also grown tremendously resulting in overgrazing and deforestation. People must cook their food which involves cutting down trees for fuelwood. Mismanagement of the land is the key cause for desertification, but the growing poor populations have no choice but to eke out an existence on increasingly marginal lands. Long fallow periods would allow the land to regain its fertility, but with the ever-increasing population this is almost impossible. Humans caused desertification. We can improve land use and farming methods to stop it.

The potential of Acacia albida for desertification control and increased productivity in Chad

Reforestation using Acacia albida has been preposed as a mechanismsfor combating desertification trends in the Sahel. This tree is characterised by a deciduous habit in the wet season; it is valuable for fodder, as a hardwood in woodwork industries, and for enhancing soil fertility of cropland. In a three-year project described in this paper, the establishment of Acacia albida platations in cultivated field in central Chad is conceived as a focal point to coordinate resource conservation and land development programmes. Several hundred thousand young trees were established and about 2500 farmers and their families participated in the revegetation programme. The success of the project must be evaluated, however, in terms of the prospects for long-term benefit and recognising the sociological problems of assistance programmes.

Recent Trends of Desertification in the Maowusu Desert, China

In the Maowusu Desert—which in the south-east encompasses part of the Yulin Region, Shaanxi Province, and in the north-west the Ih Ju League, Inner Mongolia Autonomous Region—desertification trends in relation to the impact of droughts and land-use changes were investigated. Data derived from Earth resources technology satellites (LANDSAT I and LANDSAT II, 1974–1978), and Chinese documentary sources, were used for the analysis. It was found that desert ‘expansion’ occurred during 1953–76, but the rates of expansion varied over time and space, relatively rapid desertification being observed for 1959–63 and 1971–76. The bulk of the expansion was located in the more arid Ih Ju League. The mean annual rate of areal expansion was 6.4% during 1958–71. By comparing the desertification rates with precipitation and land-use information, it was established that droughts have only accentuated the desertification process. The primary cause of desert expansion is the excessive clearing of land for rain-fed agriculture as well, of course, as overgrazing. Another contributory factor was culling of vegetation for fuel and raw materials for handicraft industries.Efforts have been expended on desert control since the mid-1950s, resulting in the arresting of desertification in some local areas. The individual success stories demonstrate that, with mass participation, effective desert control can be achieved by using low-level technology. However, the Chinese programme of desert control was not conceived as a comprehensive programme. Control activities relied almost exclusively on vegetational methods, and they were seldom coordinated with land-use policies as well as with the planning of energy supplies. The negligence of the fundamental conflict between expanding agricultural activities and desert control has led to a net desert expansion in the last 30 years. Recognition of this fundamental conflict and implementation of mitigative land-use policies, would be a major step towards resolving the desertification problem in the Maowusu Desert.