Modern Desert Research Articles

Changing particle content of the modern desert dust storm: a climate × health problem.

Climate and land use changes together are altering the particle content of desert dust storms on regional and local scales. These storms now carry a wide variety of pollutants and pathogens arising from urbanization, industrialization, mass transportation, warfare, or aerosolized waste in locations worldwide where deserts are intertwined with built infrastructure, transportation centers, and high-density human habitation. Accordingly, the modern desert dust storm has an anthropogenic particle load which presumably sets it apart from pre-industrial dust storms. Evidence for how particle content for modern dust storms is changing over the Arabian Peninsula holds relevance because dust storms are now more frequent and more severe. Furthermore, the Arabian Peninsula has asthma rates which are the highest worldwide. How the modern desert dust storm contributes to asthma and human health is a nascent issue. Meanwhile, public health decisions can benefit from a climate × health framework for dust storms, as proposed here. An imperative is testing each dust storm's particle content type, and for this, we propose the A-B-C-X model. Sampling a dust storm for its particle content data and then archiving samples for future analyses is advised. A storm's particle content data, once combined with its atmospheric data, allows a particle's source, transport, and deposition to be determined. In closing, the modern desert dust storm's changing particle content has far-reaching consequences for public health, transboundary issues, and international climate dialog. SIGNIFICANCE: Locally and regionally sourced particle pollution is a growing problem in deserts worldwide. Proposed here is a climate × health framework for studying how dust storm particles, entrained from both natural and engineered systems, may be contributing to declining human respiratory health.

Quantitative reconstruction of Early Cretaceous dune morphology in the Ordos paleo-desert and its paleoclimatic implications

Deserts are among the most important terrestrial sedimentary environments and have existed in all periods throughout Earth’s history. In contrast to modern deserts, the ability to quantitatively evaluate the area and desertification degrees of ancient deserts is limited due to the lack of unambiguous proxies. Dune morphology and their spatial arrangements directly reflect the degree of desertification of deserts. Recently, a methodology for obtaining the morphological parameters of dunes was established, although it has not been applied to ancient dunes and deserts in deep time. In the Ordos Basin, both the Early Cretaceous desert and modern deserts (Hobq Desert and Mu Us Desert) were well developed and exposed, which makes the Ordos Basin an ideal place to quantitatively evaluate the paleo-desert based on the proposed methodology. In this study, a total of 698 and 1,490 morphological parameters reflecting the Early Cretaceous desert and modern deserts in the Ordos Basin were obtained, respectively. For the Ordos paleo-desert, our results show that its area was larger and its degree of desertification was more severe than those of modern mid-latitude deserts, including the modern desert in the Ordos Basin, but were similar to those of the modern low-latitude deserts. Our results, therefore, suggest that the Ordos paleo-desert was a non-negligible and large desert during an interval of Earth’s history. Since the other controlling factors, such as regional geography and sources of both the ancient and modern deserts in the Ordos Basin, have remained nearly unchanged, we speculate that it may have been the relatively high temperature, high levels of atmospheric carbon dioxide and relatively low precipitation during the greenhouse period (i.e., Early Cretaceous) that led to the large area and severe degree of desertification of the Ordos paleo-desert.

Pollen R-values in arid central Asia for quantitative palaeo-vegetation reconstruction

Establishing the relationship between surface pollen assemblages and related modern vegetation provides a bridge for reconstructing the palaeo-vegetation succession and related climate changes. Numerous contributions have demonstrated an inconsistency between the relative abundance values of surface pollen assemblages and corresponding modern vegetation for some taxa, which is attributed to differences in their pollen production, dispersal mode and preservation potential. Consequently, the concept of R-value was introduced as a correction coefficient to counterbalance this discrepancy. Unlike most of the complex forest and grassland ecosystems, desert vegetation with fewer dominant taxa provides a simpler model to demonstrate how to use the R-value to correct this deviation. Here, we propose a scheme of Rrel median values from modern desert vegetation types based on calculated R and Rrel adjustment coefficients of the dominant taxa using surface pollen and related modern vegetation data from 145 sample plots along an east-west desert transect in the eastern arid central Asia (ACA). These data revealed that 1) taking Nitraria as a reference, Chenopodiaceae, Artemisia and Ephedra are highly represented, while Tamaricaceae, Zygophyllaceae, Asteraceae (excluding Artemisia), Calligonum and Poaceae are poorly represented. 2) the pollen representation was constrained by their pollination strategies. For example, anemophilous plants (e.g., Ephedra, Artemisia and Chenopodiaceae) are mostly over-represented, while those of entomophilous taxa (e.g., Nitraria, Tamaricaceae, Zygophyllaceae and Calligonum) are under-represented. The scheme and findings mentioned above cast a new light on the future of quantitative reconstruction of palaeo-vegetation succession in the ACA.

Physicochemical properties of surface sediments in the Taklimakan desert, northwestern China, and their relationship with oasis–desert evolution

Oasis and desert are the dominant landscapes in arid and semi-arid regions, especially in northwestern China where the oasis–desert evolution mechanisms are important for understanding modern surface processes and future environmental evolution of the region. Nevertheless, the response of the physicochemical indicators of surface sediments to oasis-desert evolution is poorly studied and it is unclear how reliable these indicators are for paleoenvironmental reconstruction. A spatio-temporal approach consisting of measurements of surface-sediment grain-size, nutrient contents and elemental ratios was used to characterize a series of modern stages of oasis-desert evolution in the Taklimakan desert. The applicability of the indicators to two sequences of alternating fluviolacustrine-wetland and aeolian sand deposits in the same region was evaluated. The results show that the oasis sediments are characterized by high contents of fine-grained particle (End-Member 1, EM1), TOC (Total organic Carbon), TN (Total Nitrogen), and MgO/SiO2, and low values of the eluvial coefficient (SiO2/(MgO + CaO + K2O + Na2O)). By contrast, the desert sediments are characterized by high values of coarse-grained particle (End-Member 3, EM3), low soil nutrients and MgO/SiO2, and an increased eluvial coefficient. In the two sedimentary sections, the physicochemical properties of the clay-silt layers resemble those of modern oasis sediments, especially washland, and the properties of the interbedded aeolian sand resemble those of modern desert deposits. The observed co-variation of grain size, soil nutrients and geochemical ratios of the surface samples shows that our approach can be used to determine the trends of past oasis-desert evolution. The reconstruction suggests that oasis formation largely depended on the development of a fluviolacustrine-wetland environment, whereas oasis degradation was closely related to strong aeolian activity. The findings provide new insights into the selection of appropriate indicators for analyzing oasis-desert sediments and for reconstructing the evolution of oasis-desert landscapes.

The canal and the pool: infrastructures of abundance and the invention of the modern desert

ABSTRACT Modernist ontologies of water physically materialise in Phoenix’s landscape: over 100 miles of canals convey water to the suburban grid, where thousands of gallons are piped into backyard swimming pools. The canal and pool are thus joined in architectural folly to move, hold, and control water in the service of sustaining the belief that dry ecologies are but supply chain problems in need of engineering solutions. These typologies reveal longstanding entanglements between the promises of modernity and aridland urbanism; and they further amplify the immense challenge of transitioning away from modern water infrastructure in the face of climate change. By using the canal and the pool as signifiers of the insidious entanglements between modernity, growth, and aridland urbanism, this article advances an historical examination of Phoenix that destabilises tropes of water scarcity as a problem to be solved but which has also created cultural perceptions of abundant water.

The Physical And Chemical Properties Of Soils For Environments Of Three Different Land/Iraq

The current study performed for the period of March 2019 to February 2020 on three different land ecosystems in three Iraqi governorates which are Sulaymaniyah, Kirkuk, and Anbar. The samples of soil are collected from nine stations that close to the pollution sources. The stations are Bazian cement plant, North Oil concentration area, the main street in the modern desert which located between longitude and latitude of (45.062554-35.577087), (44.217077 - 34.406426), (42.269622 -34.8764) respectively. Some physical and chemical factors for soils are studied where their values ranged from the electrical conductivity of (0.13 - 2.86 EC dS/m), pH (7.21 - 7.97), organic matter of (0.31 - 10.89 g/kg), the total calcium carbonate of (164.16 - 390.10 g/kg), and the positive exchange capacitance of (3.03- 25.82 (centimol+Kg-1)). While values of the exchanged positive ions are ranged (Ca+2, Mg+2, Na+1 and Potassium K+2) ((0.10 (-8.43) and (1.0 –0.01), (1.93- 0.04), (0.04). (3.79 - cimmol/kg) respectively. Whereas the values of the dissolved positive ions (Ca+2, Mg+2, Na+1 and Potassium K+1) are recorded (0.03- (3.61, (1.82-0.01), (0.01-0.67), 0.55-0.01))/L) respectively. As for negative ions, their values are recorded (dissolved bicarbonate HCO3-and dissolved chlorine (Cl-1 (0.09 (1.65-, 0.76-0.05)) centimol/L).

Paleosols and weathering leading up to Snowball Earth in central Australia

The Cryogenian Period (717–635 Ma), or ‘Snowball Earth’, was an unusually cool period of Earth history when glaciers extended to low latitudes. Past ideas on causes of this widespread glaciation include increased consumption of atmospheric carbon dioxide by silicate weathering due to continental drift into tropical paleolatitudes, or by voluminous, easily weathered volcanic tuffs. Alternatively, carbon sequestration from the atmosphere may have been intensified by advances in biomass on land or at sea. These hypotheses are tested with a new study of red siltstones of the Johnnys Creek Formation (785–717 Ma) in central Australia, where paleosols have long been recognised. Although these dolomitic red siltstones look like shales, they lack lamination. Instead, they have the massive bedding and grainsize distribution of dolomitic and calcareous loess, which precede tillites of the Areyonga Formation. Paleomagnetic studies indicate little drift from a paleolatitude of 26.2° during accumulation of the Johnnys Creek Formation. Nor does the Johnnys Creek Formation contain easily weathered volcanic ash, only local basalt flows. Paleoproductivity of the paleosols increases up section, as estimated in ppm soil CO2 from depth in paleosols to gypsic (By) and then calcic (Bk) horizons. Deepening and intensification of soil respiration reflects greater terrestrial carbon sequestration, and increased chemical weathering up section, and both would have drawn down atmospheric CO2. Comparable transition from gypsic to calcic soils in modern deserts reflects change from cyanobacterial-gypsic to fungal–algal calcic ecosystems. Snowball Earth glaciation may have been induced by evolutionary advances to eukaryotic and multicellular life on land, in the same way as Ordovician glaciation was induced by land plants, Permo-Carboniferous glaciation by trees, and Pleistocene glaciation by grasslands. KEY POINTS Johnnys Creek Formation of central Australia has paleosols dated 785–717 Ma. Little drift from paleolatitude 26.2°, and no volcanic ash, only local basalt flows. Paleosol paleoproductivity and depth of weathering increased steadily up section. Glaciation may have been induced by eukaryotic and multicellular life on land.

Preface (volume I): Quaternary paleoclimate and paleoenvironmental changes in Central Asia

The core area of Central Asia (CA), an arid Westerlies-dominated area, is crucial for analysis of interregional atmospheric circulation interactions along the Eurasian mid-latitude belt. However, it remains unclear how climate and environment in this region evolved during the Quaternary Period. Based on the articles in this special issue, this review recapitulates the spatio-temporal distribution of Quaternary sediments in CA, discusses paleoclimate and paleoenvironmental implications of various physicochemical and palaeontological proxies, and finally summarizes the paleoclimate and paleoenvironmental history since the middle Pleistocene. Field investigation and previous studies indicate that loess sediments are mainly distributed on the river terraces and windward piedmonts of Central Asian high mountains since the late Pliocene (mainly late Pleistocene). Multiple proxies analysis, e.g., grain size, geochemistry, sporopollen and magnetism, for the loess and fluvial deposits in this region reveal that the paleoclimate and paleoenvironment manifest a long-term stepwise drying or desertification trend of CA over the past 1 Myr, with at least one major drying event occurring at about ~0.5–0.6 Ma. One of the consequences is the development of the modern deserts in the Junggar Basin and the Tarim Basin. Despite the overall drying trend since the last interglacial period, the Holocene is characterized by a persistent wetting trend with millennial-scale oscillation. This special issue provides a useful glimpse into multi-scale climate and environmental changes in CA, facilitating climatic prediction in the future and climate modeling.

Soil nutrient stoichiometry on linear sand dunes from a temperate desert in Central Asia

Soil nutrient stoichiometry can influence the biodiversity, vegetation productivity, and biogeochemical cycles in terrestrial ecosystems. However, the soil nutrient status, distribution patterns, and driving factors on sand dunes in modern deserts were still unclear. The soil C, N, P, and K contents in 65 plots across two continuous linear sand dunes (220 m × 110 m) located in the Gurbantunggut Desert, a typical temperate desert in Central Asia, were investigated by the traditional statistical, geostatistical, and structural equation modeling (SEM) techniques. Results indicated that soil C, N, and P contents were low and presented remarkable interactions with each other. The order of soil nutrient deficiency in the sand dunes was C > N > P > K, in which soil C exhibited a higher accumulation rate than N and P based on allometric analysis. Soil C, N, P, and their ratios to K exhibited an obvious U-shaped curve opposite to the shape of the sand dune, had strong spatial dependence (structural variance ratios: 81.4–94.3%), and presented evidently longitudinal zonal distribution patterns along the sand dunes. Pearson's correlation analysis and canonical correspondence analysis demonstrated that the topographic (slope position, relative height, convexity, and curvature), vegetation (herbaceous richness, abundance, coverage and biomass, and deep-rooted small shrubbery), soil abiotic (pH, electronic conductivity, and soil water content), and soil biotic (i.e., biological soil crust) factors interacted with each other and were significantly correlated with most soil stoichiometric parameters. The SEM analysis further demonstrated that the topography was the most direct driving factor influencing soil C, N, and P and their ratios to K on sand dunes. The results revealed that sand dune fixation and lowering promoted the formation of a stable and sustainable soil–plant relationship in temperate deserts of Central Asia.

The first known fossil Uma: ecological evolution and the origins of North American fringe-toed lizards

BackgroundFossil evidence suggests that extant North American lizard genera (north of Mexico) evolved during the Miocene. Although fossils of the clade Phrynosomatidae (spiny lizards and sand lizards) have been reported, there have been no previously described fossils of the fringe-toed sand lizards (Uma). In the extant biota, Uma inhabit arid deserts, and members of the western clade of Uma are restricted to sand dunes or other habitats containing fine-grained sand.ResultsI describe the first known fossil of Uma and refer the fossil to the total clade of Uma with an apomorphy-based diagnosis. The fossil is a partial premaxilla that was found in the Miocene strata of the Dove Spring Formation of southern California, dating to 8.77 Ma. The paleoenvironment of the Dove Spring Formation was semiarid and contained ephemeral streams that facilitated deposition, and there is no evidence of sand dune deposits in the strata containing the locality from which the Uma fossil was found. Divergence time analyses of a concatenated molecular dataset with four fossil calibrations support a Neogene origin of the total clade of Uma and of the crown clade of Uma. Those analyses also estimated a Neogene divergence between Uma scoparia and the Uma notata complex. Multispecies coalescent analyses with one fossil calibration inferred a Paleogene origin for the total clade of Uma and a Pliocene or Pleistocene divergence between Uma scoparia and the Uma notata complex. The fossil and the total and crown clades of Uma precede the evolution of modern desert ecosystems in the southwestern United States and northern Mexico by millions of years.ConclusionsThe total clade and the crown clade of Uma were not restricted to arid deserts throughout their evolutionary histories. I demonstrate that an apomorphy-based diagnosis can be used to identify fossils of isolated skeletal elements for at least one clade of phrynosomatid lizard, and suggest exercising caution when using environmental tolerances of extant taxa to hypothesize paleoecological reconstructions.

Dust provenance in Pan-third pole modern glacierized regions: What is the regional source?

To differentiate the source of aeolian dust between the desert sources from Pan-third pole and high mountain glaciers, therefore, we investigated the spatial variability of aeolian dust sources in the Pan-third polar region. The question of whether such changes reflect variable transport pathways from a unique source in the western China area was addressed. That is, the SrNd radiogenic isotope composition of modern desert samples do not support the hypothesis of a single dust provenance at higher elevation mountain glaciers by long-distance transport; regional sources also play a significant role. Based on previous studies and the data from this study, the five isotopic regions were divided, which are controlled by the geological characteristics in western China. The results suggest that mineral dust deposited into the high-mountain glaciers originated from the free ice region because of glacier melting and the physical and chemical erosion of rocks from the surrounding mountains by local wind systems. The Pb isotopic data further demonstrated that natural dust is the source of Pb for the high-mountain glaciers of Pan-third pole. These results provide an exhaustive documentation of the isotopic signature of the regional dust reaching the glacier regions.

Meandering rivers in modern desert basins: Implications for channel planform controls and prevegetation rivers

The influence of biotic processes in controlling the development of meandering channels in fluvial systems is controversial. The majority of the depositional history of the Earth's continents was devoid of significant biogeomorphic interactions, particularly those between vegetation and sedimentation processes. The prevailing perspective has been that prevegetation meandering channels rarely developed and that rivers with braided planforms dominated. However, recently acquired data demonstrate that meandering channel planforms are more widely preserved in prevegetation fluvial successions than previously thought. Understanding the role of prevailing fluvial dynamics in non- and poorly vegetated environments must rely on actualistic models derived from presently active rivers developed in sedimentary basins subject to desert-climate settings, the sparsest vegetated regions experiencing active sedimentation on Earth. These systems have fluvial depositional settings that most closely resemble those present in prevegetation (and extra-terrestrial) environments. Here, we present an analysis based on satellite imagery which reveals that rivers with meandering channel planforms are common in modern sedimentary basins in desert settings. Morphometric analysis of meandering fluvial channel behaviour, where vegetation is absent or highly restricted, shows that modern sparsely and non-vegetated meandering rivers occur across a range of slope gradients and basin settings, and possess a broad range of channel and meander-belt dimensions. The importance of meandering rivers in modern desert settings suggests that their abundance is likely underestimated in the prevegetation rock record, and models for recognition of their deposits need to be improved.

Wisdom dwells in places: What can modern farmers learn from ancient agricultural systems in the desert of the Southern Levant?

Farming in drylands has always been challenging, however, modern technologies that allow irrigation by using distant water have sparked renewed interest in desert agriculture. Using imported water liberates the modern farmers from one of the major limitations created by this extreme environment, but the high price of the water, along with natural processes such as salinization and soil erosion, can make modern agriculture unprofitable.In the Negev Highlands desert of the Southern Levant, new agriculture enterprises have recently been established on the same soils that were cultivated for 600–700 years by ancient residents who constantly contended with environmental challenges. Therefore, it makes sense to ask whether the modern farmers can improve their methods using the long-term experience embodied in the remnants of the ancient agricultural systems. Using an interdisciplinary approach combining geomorphology, hydrology, archaeology and sociology, we show that the modern farmers face serious problems of soil erosion, soil salination and high price of water. Surprisingly, rain and floods are considered a negative factor for modern desert agriculture. We conclude that adapting and integrating some of the ancient methods within modern desert agricultural practices may turn the desert precipitation from a burden to a blessing.

Dynamic Vegetation Simulations of the Mid‐Holocene Green Sahara

AbstractThe “Green Sahara” is a period when North Africa was characterized by vegetation cover and wetlands. To qualitatively identify the orbital‐climatic causation of the Green Sahara regime, we performed dynamic vegetation model (LPJ‐GUESS) simulations, driven by climate forcings from coupled general circulation model (EC‐Earth) simulations for the mid‐Holocene, in which the vegetation is prescribed to be either modern desert or artificially vegetated with a reduced dust load. LPJ‐GUESS simulates a vegetated Sahara covered by both herbaceous and woody vegetation types consistent with proxy reconstructions only in the latter scenario. Sensitivity experiments identify interactions required to capture the northward extension of vegetation. Increased precipitation is the main driver of the vegetation extent changes, and the temperature anomalies determine the plant functional types mainly through altered fire disturbance. Furthermore, the simulated vegetation composition also depends on the correct representation of soil texture in a humid environment like Green Sahara.

Nature and origin of the nonsulfide zinc deposits in the Sierra Mojada District, Coahuila, Mexico: constraints from regional geology, petrography, and isotope analyses

The Sierra Mojada District comprises multiple types of near-surface mineral concentrations ranging from polymetallic sulfide zones, “nonsulfide Zn” (NSZ) deposits, and a silver-rich Pb carbonate deposit hosted by lower Cretaceous carbonate strata. Hypogene concentrations of Fe-Zn-Pb-Cu-Ag sulfides and sulfosalts are locally preserved and are associated with hydrothermal dolomite and silica. Alteration mineralogy and sulfur isotope data suggest primary Zn-Pb-Ag mineralization from circa 200 °C hydrothermal fluids. The NSZ deposits dominantly consist of smithsonite and hemimorphite associated with local Mn-Fe oxides. The Red Zinc Zone consists of strata-bound zones dominantly of hemimorphite that fills pores in residual and resedimented Fe oxides. The White Zinc Zone shows local dissolution features, including internal sediments interbanded with and cemented by smithsonite. Similar Pb isotopic compositions of smithsonite, hemimorphite, and cerussite to Sierra Mojada galena document that the NSZ deposits originated from polymetallic carbonate-replacement sulfide deposits, with flow of metal-bearing groundwater being controlled by local topography and structural features in this extensional terrane. Oxygen isotope values for Sierra Mojada smithsonite are relatively constant (δ18OVSMOW = 20.9 to 23.3‰) but are unusually low compared to other supergene smithsonites. Using δ18OVSMOW (− 8‰) of modern groundwater at nearby Cuatrocienegas, smithsonite formational temperatures are calculated to have been between 26 to 35 °C. Smithsonite precipitation was favored by near-neutral conditions typical of carbonate terranes, whereas hemimorphite precipitated by reaction with wallrock silica and locally, or episodically, more acidic conditions resulting from sulfide oxidation. Transition to, and stabilization of, the modern desert climate over the past 9000 years from the Late Pleistocene wetter, cooler climate of northern Mexico resulted in episodic drawdown of the water table and termination of local supergene metal mobilization.

Isotopic niche variation from the Holocene to today reveals minimal partitioning and individualistic dynamics among four sympatric desert mice

Species interact with each other and their environment over a range of temporal scales, yet our understanding of resource partitioning and the mechanisms of species coexistence is largely restricted to modern time-scales of years to decades. Furthermore, the relative magnitudes of inter- vs. intraspecific variation in resource use are rarely considered, despite the potential for the latter to influence a species' ability to cope with changing environmental conditions. Modern desert rodent communities are thought to be strongly structured by competitive interactions, with niche partitioning of food resources hypothesized to explain the coexistence of multiple sympatric granivores. Yet the stability of niche dynamics over extended temporal scales within desert rodent communities is unknown. I examined the isotopic niche dynamics of four common sympatric desert mice (three granivores: Chaetodipus formosus, Perognathus longimembris and Reithrodontomys megalotis, and one omnivore: Peromyscus maniculatus) in the Smoke Creek Desert of northwestern Nevada using 13 C and 15 N isotopes obtained from "Modern" (2008-2013 CE), "Historical" (1989-2005 CE) and Holocene fossil specimens spanning the last c. 7,500years. I found significant variation in niche position, niche breadth and interspecific niche overlap of these species through time. The niche breadth dynamics of the cricetids (P.maniculatus and R.megalotis) were positively correlated with one another, while the niche breadth dynamics of the heteromyid C.formosus were negatively correlated with those of all other species. Body size, dietary functional group, palaeoenvironmental trends and time-averaging provided little explanatory power. Importantly, Modern and Historical patterns of resource use and partitioning differed from Holocene baselines in terms of decreased niche overlap and in the absolute and relative position of each species' niche in at least one isotopic axis. These observations suggest that each species' resource use changed individualistically over the Holocene, hence niche dynamics are poorly explained by the hypothesis of temporally stable species interactions at millennial time-scales. Furthermore, changes to the resource base over the last century (likely due to the spread of invasive cheatgrass) may be increasing resource partitioning in the Modern, pushing species past their baseline ranges of resource use variation.

Late Quaternary optically stimulated luminescence (OSL) chronology and environmental changes in the Hobq Desert, northern China

The Hobq Desert (HD) is distributed along the south bank of the Yellow River in northern China. Proximation to the East Asian summer monsoon limit makes this desert sensitive to fluctuations of monsoonal intensity. However, environmental changes in the HD during late Quaternary are poorly known due to lack of extensive field investigation and appropriate dating materials for radiocarbon dating. In this study, seven field profiles were examined and a chronology framework based on quartz optically stimulated luminescence (OSL) was established to reconstruct environmental changes in the HD. The results suggested two possible periods when lake existed during late Quaternary. The older paleo-lake covering most part of the HD was likely to be formed before ∼160 ka and vanish at ∼100 ka, whereas the younger paleo-lake, which was much smaller, existed at ∼10 ka. The vanishment of the older paleo-lake was probably triggered by a tectonic event, while the existence of the younger paleo-lake was assumed as a response to humid climate in the beginning of Holocene. Meanwhile, the results also showed that modern desert landscape in the HD began at ∼27 ka, and kept expanding during the Holocene. The climate variations dominated the development of desert landscape in the beginning, and human activity enhanced the desertification at least since ∼1 ka.

The impact of courtyard design variants on shading performance in hot- arid climates of Iran

This article focuses on the impact of courtyard design variants on shading performance of traditional courtyard houses in hot-arid climate of Iran. The aim is to identify the best design model for courtyard, regarding geometrical properties and orientation, to improve thermal comfort in the modern desert houses. To that end, ten traditional courtyard houses with various orientations, dimensions, and proportions from hot-arid climate of Kerman are selected. A three dimensional numerical models are developed using Design Builder software to determine shaded and sunlit areas for each case, based on a set of equations which were derived through analyzing the correlation between the sun location at any time and geometrical properties of courtyard. A new index is proposed to evaluate thermal comfort in courtyards considering average daily and annually temperatures. Shading and sunlit area are associated in this index to achieve the maximum comfort temperature during a year, and the relationships between this index and courtyard’s geometrical properties and orientation are investigated. Results show that the courtyard’s design variants have considerable influence on the shading performance of courtyards. As conclusion, all data sets were integrated to propose an optimized design model for courtyard as a passive cooling strategy.

Tectonic and environmental controls on Palaeozoic fluvial environments: reassessing the impacts of early land plants on sedimentation

The apparent increase in occurrence of meandering fluvial channel systems in the Middle Palaeozoic has long been related to the effects of land-plant colonization. However, evidence for meandering channels in non-vegetated settings is shown by pre-vegetation successions on Earth, from the prevalence of meandering channels on Mars, from physical modelling of meandering channels, and from non-vegetated channels in modern desert basins. In addition, early land plants had small dimensions, were limited in their occurrence, and were dependent on environmental factors. Here, we question the capacity of early land plants to impose the major impacts suggested by current models. We propose that the sudden widespread occurrence on Earth of fluvial deposits indicative of the accumulation of meandering river systems in the Middle Palaeozoic was primarily an effect of environmental and tectonic conditions that prevailed during this period. These conditions induced a worldwide increase in the proportion of meandering rivers, which in turn helped favour the appropriate environment for land-plant colonization of the continents. We propose that land plants opportunistically took advantage of an appropriate global environment, which enabled them to thrive in continental environments. Fluvial environments characterized by single-channel systems and stable floodplains facilitated the greening of the land.

Detecting modern desert to urban transitions from space in the surroundings of the Giza World Heritage site and Greater Cairo

Abstract During the last decades, Greater Cairo, Egypt, is increasing in population and in built-up extension. Some of the new buildings are informal, constructed in absence of government planning processes, and threaten the Heritage Cultural Site of the Giza Pyramids. In addition, the fertile land of the Nile floodplain is being urbanized despite the government's building prohibition since the 1990s. Therefore, constant monitoring of construction activity is crucial in the rapidly changing environment of this area. Here, we present a data fusion approach that overcomes the limitations of single medium resolution sensor approaches, and also identifies areas in transition from desert to urban. We use multi-temporal multi-sensor supervised land use classification and include a new land use class for detecting undefined disturbances. Synthetic aperture radar (SAR) data is combined with multi-spectral data for creating the land use land cover (LULC) maps using artificial neural networks (ANN). Specifically, ERS SAR data is combined with Landsat 5TM for 1998 and Envisat ASAR IMS with Landsat 7 ETM+ for 2004 and 2010. With this data fusion approach, it is measured an increase of 73% of Greater Cairo built-up extent from 1998 to 2010. Finally, we show the relationship between the aforementioned disturbances and the new built-up areas, detecting 26% of the total new built-up areas constructed from 1998 to 2010 where undefined disturbances were identified in previous land use maps.