Nick Middleton

World atlas of desertification.

This text aims to summarize the state of scientific knowledge on the drylands of the globe. It explores the current stage of understanding of desertification as well as its extent and possible solutions. The book argues that desertification is one of the worlds most pressing environmental problems and that it is a global issue which is accelerating. This edition has been revised and expanded to include updated computer images of desertification, as well as fuller descriptions and explanations of the issues concerned. Using detailed data of the physical and chemical status of soil degradation provided by the Global Assessment of Soil Degradation, the book is fully referenced and covers topics including: desertification and global warming; monitoring on the ground and by remote sensing; vegetation and degradation; local action; cultural factors; financial issues; land reclaimations; the political economy and desertification; and desertification and refugees.

Saharan dust storms: nature and consequences

This paper reviews recent work on the role of Saharan dust in environmental change, the location and strength of source areas, the transport paths of material away from the desert, the rates of Saharan dust deposition, the nature of that material (including PeriSaharan loess) and the changing rates of dust activity in response to long and short-term climatic changes. The Sahara produces more aeolian soil dust than any other world desert, and Saharan dust has an important impact on climatic processes, nutrient cycles, soil formation and sediment cycles. These influences spread far beyond Africa, thanks to the great distances over which Saharan dust is transported. The precise locations of Saharan dust source areas are not well known, but data from the Total Ozone Mapping Spectrometer (TOMS) suggest two major source areas: the Bodele depression and an area covering eastern Mauritania, western Mali and southern Algeria. Trajectories of long-distance transport are relatively well documented, but the links between source areas and seasonal Saharan dust pathways are not. However, it is possible that Harmattan dust from the Bodele depression may not be the source of the prominent winter plume over the tropical North Atlantic, as is often suggested in the literature. Few of the data on particle size characteristics of Saharan dust are derived from major source areas or from Africa itself. Saharan dusts sampled from the Harmattan plume and over Europe are dominated by SiO2 and Al2O3, a characteristic they share with North American and Chinese dusts. The concentrations of these two major elements are similar to those found in world rocks. PeriSaharan loess is conspicuous by its relative absence, considering the Saharas dominance of the global desert dust cycle both in the contemporary era and through the geological past. In recent decades, the frequency of Saharan dust events has varied markedly in response to climatic factors such as drought and anthropogenic disturbance of desert marginal surfaces. Nonetheless, the Saharas two major dust sources are little affected by human activities and are in fact located in areas that receive very low rainfall totals. Hence, the Sahara does not fit the postulated global picture of a peak in dust storm activity in the 100–200-mm mean annual rainfall zone.

Dust-Storm Source Areas Determined by the Total Ozone Monitoring Spectrometer and Surface Observations

Abstract Dust storms are recognized as having a very wide range of environmental impacts. Their geomorphological interest lies in the amount of deflation and wind erosion they indicate and their role in loess formation. Atmospheric mineral-dust loading is one of the largest uncertainties in global climate-change modeling and is known to have an important impact on the radiation budget and atmospheric instability. Major gaps remain in our understanding of the geomorphological context of terrestrial sources and the transport mechanisms responsible for the production and distribution of atmospheric dust, all of which are important in reducing uncertainties in the modeling of past and future climate. Using meteorological data from ground stations, from the space-borne Total Ozone Monitoring Spectrometer (TOMS), and from the National Center for Environmental Prediction–National Center for Atmospheric Research reanalysis project, we illustrate the key source regions of dust and demonstrate the primacy of the Sahara. Objectively defined source regions for the Sahara are determined from eigenvector techniques applied to the TOMS data. Other key regions include the Middle East, Taklamakan, southwest Asia, central Australia, the Etosha and Mkgadikgadi basins of southern Africa, the Salar de Uyuni (Bolivia), and the Great Basin (United States). In most of these regions, large basins of internal drainage, as defined from a digital elevation model, are dust sources where the near-surface atmospheric circulation (determined by calculated means of potential sand flux) is favorable for dust mobilization. Surface observations indicate some regions as being important that do not appear on the TOMS maps. Possible reasons for these discrepancies are explored.

Saharan dust: sources and trajectories

The Sahara is the world’s largest source of aeolian desert dust, but precise information on specific sources of this material is poor and sometimes contradictory. This paper uses daily data from the Total Ozone Mapping Spectrometer (TOMS) for 1999 to identify source areas for major dust events and their trajectories of long-range transport. Two major source areas are identified: the Bodele depression and an area covering eastern Mauritania, western Mali and southern Algeria. Both of these major dust sources are primarily driven by natural factors since they are little affected by anthropogenic activities.

THE CHANGING FREQUENCY OF DUST STORMS THROUGH TIME

Dust storms are major, but under-studied actors in the worlds drylands. Not only are they an important manifestation of desertification and land degradation, but they also have a whole suite of important environmental impacts, including possible rainfall suppression (Maley, 1982), fertilization of offshore areas, and disturbance to satellite communications. It is therefore important to ascertain whether their frequency and extent is changing. An increasing dust-storm incidence could be both a manifestation of and a contributor to global change.By analysing long-term meteorological records for a large number of areas (the Great Plains of the USA, the USSR, Morocco, The Arabian Gulf, Australia, the Sahel-Sudan zone of Africa, China, Mongolia and Mexico) certain conclusions can be drawn. The first of these is that there is no one global pattern of dust-storm frequency trend. Some stations (e.g. in the Sahel) show a clear upward trend of great severity, others show a downward trend (e.g. Mexico City), while others show a more cyclical pattern. In many cases it is evident that essentially natural processes (precipitation totals, snow cover, wind strength) determine the frequency of dust events in any one year. It has also been possible to show the importance of runs of drought years (e.g. in the High Plains in the 1930s, and in the Sahel zone of Africa in the 1970s and 1980s). Elsewhere, however, various human activities have been significant in determining dust-storm frequency variations: the introduction of centre-pivot irrigation in the High Plains, the abstraction of water from the Owens and Mono basins in California, the disruption of surfaces by construction activity and vehicle use (e.g. in Ulan Bator, Mongolia), and the deliberate stabilisation of susceptible surfaces (e.g. the Lake Texcoco scheme in Mexico).

Tracking desertification on the Mongolian steppe through NDVI and field-survey data

Abstract Changing environmental and socio-economic conditions make land degradation, a major concern in Central and East Asia. Globally satellite imagery, particularly Normalized Difference Vegetation Index (NDVI) data, has proved an effective tool for monitoring land cover change. This study examines 33 grassland water points using vegetation field studies and remote sensing techniques to track desertification on the Mongolian plateau. Findings established a significant correlation between same-year field observation (line transects) and NDVI data, enabling an historical land cover perspective to be developed from 1998 to 2006. Results show variable land cover patterns in Mongolia with a 16% decrease in plant density over the time period. Decline in cover identified by NDVI suggests degradation; however, continued annual fluctuation indicates desertification – irreversible land cover change – has not occurred. Further, in situ data documenting greater cover near water points implies livestock overgrazing is not causing degradation at water sources. In combination of the two research methods – remote sensing and field surveys – strengthen findings and provide an effective way to track desertification in dryland regions.

Climatic Controls on the Frequency, Magnitude and Distribution of Dust Storms: Examples from India/Pakistan, Mauritania and Mongolia

Analysis of terrestrially observed meteorological data is used to fill some of the gaps in our knowledge of the dust storm systems in a number of world regions.

Explaining spatial variations in climate hazard impacts in western Mongolia

The winter of 2009/2010 induced a mass loss of livestock known as dzud in Mongolia. We examine spatial heterogeneity in this livestock loss in a western Mongolian province using a semi-structured questionnaire, key informant interviews, meteorological station data, and two datasets derived from satellite imagery. We identify marked local variability in the impact of winter 2009/2010 demonstrated by a striking difference in livestock mortality between three Altai mountain districts and three Gobi desert districts. We explain this pattern with reference to site-specific circumstances. We ascertain a counter-intuitive pattern of milder winters with less snow in Mountain districts when compared to Desert districts, a contrast that was particularly acute in the winter of 2009/2010 which was uncommonly long and hard, with particularly deep and widespread snow cover in the Desert, but unusually mild in the Mountains. Examination of possible drivers of dzud vulnerability at the household and community levels—wealth and herder experience—found virtually no influence on livestock losses, although a large majority of herder households were characterised by a general lack of alternative income opportunities. The severity of conditions undermined many Desert herders’ coping and adaptive strategies, including communal pooling, although those who managed to move their herds in response to the 2009/2010 dzud suffered markedly smaller livestock losses. Limited government capacity, partly influenced by remoteness, further increased vulnerability in the Desert districts where the deep snow restricted access to dzud relief assistance. Implications for hazard management and governance are discussed, as are recent policy initiatives.

Contraction of the Gobi Desert, 2000-2012

Abstract: Deserts are critical environments because they cover 41% of the world’s land surface and are home to 2 billion residents. As highly dynamic biomes desert expansion and contraction is influenced by climate and anthropogenic factors with variability being a key part of the desertification debate across dryland regions. Evaluating a major world desert, the Gobi in East Asia, with high resolution satellite data and the meteorologically-derived Aridity Index from 2000 to 2012 id entified a recent contraction of the Gobi. The fluctuation in area, primarily driven by precipitation, is at odds with numerous reports of human-induced desertification in Mongolia and China. There are striking parallels between the vagueness in defining the Gobi and the imprecision and controversy surrounding the Sahara desert’s southern boundary in the 1980s and 1990s. Improved boundary definition has implications for understanding desert “greening” and “brown ing”, human action and land use, ecological productivity and changing climate parameters in the region. The Gobi’s average area of 2.3 million km

Determining contribution of sand dune potential sources using radionuclides, trace and major elements in central Iran

The present research describes a first attempt to use quantitative fingerprinting to quantify source contributions of sand dunes. Forty-nine surface samples from the main potential sources within Yazd-Ardekan Plain in the central Iran were collected and compared with eight samples of sand dunes, collected on various sites of Ashkzar erg. Three major categories of sand dune source were identified: young terraces and gravel fans (Qt2), clay flat (Qc), and gypsiferous marl (Egm). After sample preparation, concentrations of geochemical elements such as rare earth element (REE), major and trace elements, and isotopes of strontium (87Sr and 86Sr) and neodymium (143Nd and 144Nd) were measured. The results indicated, based on discriminant function analysis, 81.6% of the samples to be correctly assigned to their source areas. The mean contributions from Qt2, Qc, and Egm sources in the study area were estimated as 59, 30, and 11%, respectively. The efficiency coefficient for mixing model was calculated to be 0.99, which represents that the fingerprinting technique has a great potential for apportionment of sand dune sources.