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In this paper, performance degradation and reliability evaluation of crystalline silicon photovoltaic modules deployed in desert climate was investigated based on the more than 7-year tracking test. It is found that peak power standard deviation first increased with time, reaching the peak when modules operated for 3 years, and then continuously decreased. Then, relationship among power warranty, power degradation rate and tolerance on maximum power is revealed for the first time. If 1% of module failures during warranty period is allowable, the 30-year warranty can be realized when degradation rate is 0.4–0.6 %/year with tolerance 0 ∼ +5% and 0 ∼ +3%, or degradation rate is 0.5 %/year with tolerance ±5% and ±3%, or degradation rate is 0.4 %/year with tolerance ±10%, ±5% and ±3%. Finally, reproducibility of power measurement is introduced for more accurately evaluating module performance degradation and reliability. Meanwhile, determination procedure of reproducibility for module electrical performance is systematically set forth. It is found that power warranty period can be prolonged if reproducibility is considered. The results obtained in this paper can provide new insights into performance degradation, reliability assessment and power warranty for fielded crystalline silicon solar modules. [ABSTRACT FROM AUTHOR]

• This paper summarizes the performance of multi-crystalline, mono-crystalline and silicon heterojunction photovoltaic (PV) arrays operating in desert climate. • Indoor characterization of all PV modules from seven arrays was performed to determine the degradation rate. • Visual and Electroluminescence (EL) inspections were performed to gain more insight on the module failure. • Encapsulant yellowing, back sheet cracking and cell cracking were the most prominent failure modes observed after 5-years operation in the desert climate. Performance and reliability of photovoltaic (PV) systems are important for the deployment of PV in desert climate. In this study, we investigate the performance and reliability of multi-crystalline, mono-crystalline and silicon heterojunction PV arrays operating in the field for 5-years from 2014 to 2018 under desert climate. From data monitoring and performing visual inspection at the field, a drop in the energy yield and the presence of various visual defects were observed and therefore further in-depth analysis was required to identify the potential of main cause of the performance losses. For the (Multi_D), (Multi_E), (Multi_F), (Mono_G), and (SHJ_H) arrays a degradation rate of −2.65 %/year, −1.91 %/year, − 0.14 %/year, − 1.59 %/year and − 0.62 %/year, respectively, was calculated using the RdTool. From each array, all modules returned from the field to perform indoor current–voltage (IV) measurements at Standard Testing Condition (STC) and at different irradiance and temperature operating conditions. The electrical parameters of these modules were analyzed and the degradation rate was estimated by comparing the STC values provided by the manufacturer with the STC values measured after 5-years exposure in desert climate. From the seven difference manufacturers, multi-crystalline silicon (Multi_A), (Multi_B) and (Multi_E) showed the lowest annual degradation rate below 1 %/year. Multi-crystalline silicon (Multi_D) and mono-crystalline silicon (Mono_G) showed the highest PV module power degradation of −3.0%/year and 6.3 %/year, respectively. Further, Encapsulant yellowing, back sheet cracking and cell cracking were the most prominent failure modes observed during the first 5-years of operation in the field. [ABSTRACT FROM AUTHOR]

Desertification is a global challenge threatening the sustainable development of humans. Recently, a concept of employing algae-based biological soil crust (BSC) for desertification control in arid and semi-arid zones is becoming popular. In this paper, we focused on the screening of algal strains, study of BSC formation mechanisms, and optimization of critical parameters, which are important issues for the successful application of algae-based BSCs. In addition, some cases of practical application and field survey related to the use of algae-based BSCs in arid and semi-arid zones are presented. By the end of this paper, challenges and prospects of employment of algae-based BSC for desertification control are discussed in detail. It is expected that with the deeper understanding of algae-based BSC, more research can be conducted to promote its application in desertification control for humans' sustainable development. • Cyanobacteria and microalgae are major microorganisms in some soil crust. • Biological soil crusts are of importance to the ecosystem in arid and semi-arid zones. • Formation mechanisms of algae-based biological soil crust are reviewed. • Critical parameters impacting the development of soil crust are intensively studied. • Some problems must be addressed for the algae-based biological soil crust in deserts. [ABSTRACT FROM AUTHOR]

Oasification is a complex oasis expansion and ecological processes caused by climate changes and human activities under available water supply in arid and semiarid regions. The process can effectively improve soil productivity, vegetation cover, and biomass production in fighting against land degradation, such as desertification and soil erosion. However, the significance of oasification has not yet reached the general cognition compared to desertification, which is regarded as one of the most severe global eco-environmental issues. This paper identifies desertification and oasification processes and their perspectives in cognition. The implication of oasification in combating desertification and controlling land degradation is emphasized by the justification between desertification and oasification processes. As opposite process of desertification, the oasification is an unable evasive process that can provide positive environmental effects in the control of desertification, ecological restoration, and land rehabilitation. According to the interaction of climatic variations and human activities, the oasification processes is classified into six main forms: natural oasis evolution process, engineering forest construction, conversion of natural landforms into farmlands, urban encroachment, constructed environments, and coupled ecosystems. These processes gradually modify the productive capacity of soils, increase vegetation cover for restoring degraded lands, and improve the living environment for human settlement and sustainability of an oasis ecosystem. Moreover, an overview of oasification research is detailed, and Northwest China as an example is used to illustrate the progress of the oasification research in recent decades. Currently, the oasification process and its mechanistic research still remain less concern in the arid and semiarid regions. A new science framework of the oasification research is proposed to effectively deal with ecological and environmental issues in the arid and semiarid regions. • Desertification and oasification and their perspectives are identified. • Implication of oasification is emphasized in comparison with desertification. • Oasification processes are classified into six main forms. • Overview of oasification research is detailed and illustrated in Northwest China. • A new science framework of the oasification research is proposed. [ABSTRACT FROM AUTHOR]

Abstract Advection fog is the sole source of water for many near-the-sea arid areas worldwide such as the lomas , i.e. fog-dependant landscapes of the coastal zone of Peru and Northern Chile, where deforestation occurred since 16th century, leading to a progressive and severe desertification. There, today's local socio-ecological systems suffer from lack of freshwater because they cannot rely anymore on the contribution of fog captured by vegetation. This paper presents the results of an experimental reforestation project carried out in Mejia (Peru), where tree seedlings of five native and exotic species were planted in two permanent plots in 1996. Part of the seedlings were irrigated during the first three years after planting, others not. The irrigation was carried out thanks to water harvesting by large fog collectors. From the third year onwards, all trees relied only on fog water collected by their canopy. Survival rate, height, and root-collar diameter were monitored until 2010, when also the soil carbon and nitrogen stocks were measured. Fifteen years after the planting, about 65% of trees were still alive and growing, and reforestation had induced substantial carbon sequestration both above- and below-ground. Of the tree species, Acacia saligna was definitely best performing than the other, with most of the above ground carbon stored in its biomass and a consequent high efficiency as natural fog collector. Overall, the combination of fog collection by nets and the plantation of trees showing good fog collection capacity, represented a successful strategy for allowing reforestation of arid environments and induced fast and substantial carbon sequestration. Greater efforts should be thus devoted for this purpose, paying special attention to the selection of the most suitable tree species to plant, especially looking at the local biodiversity. This work is dedicated to the memory of Professor Mario Falciai, passed away in 2015, who firstly conceived the experiment and attended all the work since 1996, bringing in our University the idea of Fog Collection for sustainable water management. Graphical abstract Unlabelled Image Highlights • Advection fog is the sole source of water for many near-the-sea areas worldwide. • We present the results of a long-term reforestation project in the Atacama Desert. • Trees were irrigated with artificially fog-collected water for three years. • After 15 years from planting, about 65% of trees were still alive and growing. • Reforestation induced fast and substantial carbon sequestration. [ABSTRACT FROM AUTHOR]

Abstract: A field study was conducted in the Negev Desert over three seasons: June (summer), October (autumn), and April (spring). Cellulose of plant or paper origin was added to the study soils. The concentration of cellulase in the soil was determined by monitoring the rate of solubilization of chromophoric molecules covalently linked to artificial insoluble cellulose (cellulose-azure). The amount of CO2 evolved from the soil was also evaluated at 60-day intervals. In this paper, we demonstrate that significant differences (p<0.01) in the cellulase concentration in desert soils are mainly due to the time period during which organic matter was incorporated into the soil. Data are presented showing changes in cellulase concentrations in the soil as a response to different cellulose sources (plant and paper origin) throughout the year. The results of our field experiments show that the cellulase concentration in the soil surrounding cellulose (paper) is higher during the summer than during the other seasons. The concentration of cellulase associated with fresh organic matter was found to be double that associated with paper. CO2 evolution was higher in soil samples supplemented with organic matter than in control samples. This study demonstrates that the concentration of cellulase in desert soil changes over the year and is influenced by the cellulose source and by the quality of the cellulose incorporated in the soil. [Copyright &y& Elsevier]

Summary: In a research article, published in “Basic and Applied Ecology” in 2000, the authors T. Becker and S. Getzin described dynamics and characteristics of the so-called fairy circles in Kaokoland (North-West Namibia). They stated that the foraging activity of the harvester termite Hodotermes mossambicus Hagen, which is widely distributed in Southern Africa, results in conspicuous, circular, vegetationless patches (fairy circles), surrounded by densely packed grass tussocks. The authors concluded that a) foraging and nesting characteristics of H. mossambicus determine the occurrence of the fairy circles b) grass species richness and assemblage influences the harvesting pattern of H. mossambicus c) differences in the intensity of foraging of H. mossambicus may cause different diameters of the circular forms d) the diameter of the circles is limited by the temperature sensitivity of H. mossambicus Becker and Getzin''s statements regarding basic termite biology are based on literature data published in the late 1950''s and the author''s fieldwork was restricted to few weeks in March/April 2000. The objective of the present opinion paper was to write a comment upon the findings of Becker and Getzin and to encourage future research, which will result in a sound theory about the origin of the fairy circles in Namibia. In einem wissenschaftlichen Beitrag im Journal “Basic and Applied Ecology” (2000) beschrieben T. Becker und S. Getzin Dynamik und Eigenschaften der sogenannten Feenkreise in Kaokoland (Nord-West Namibia). Sie berichteten, dass die Ernteaktivität der im südlichen Afrika weit verbreiteten Termite Hodotermes mossambicus kreisrunde, vegetationslose, von dichten Grasbüscheln umgebene Flecken (Feenkreise) verursacht. Die Autoren kamen zu dem Schluss, dass a) Ernteaktivität und Nesteigenschaften von H. mossambicus das Auftreten der Feenkreise bestimmen b) Artenreichtum der Gräser sowie deren Ansammlung das Erntemuster von H. mossambicus beeinflussen c) Intensitätsunterschiede in der Ernteaktivität von H. mossambicus zu unterschiedlich großen Feenkreisen führen kann d) der Durchmesser der Feenkreise duch die Temperaturempfindlichkeit von H. mossambicus beeinflusst wird Becker und Getzin''s Befunde zur Termitenbiologie stützen sich auf Literaturdaten aus den 1950''er Jahren und die Feldarbeit der Autoren war auf wenige Wochen im März/April 2000 beschränkt. Das vorliegende “Opinion Paper” kommentiert die Befunde von Becker und Getzin und will zu weiterer Forschung ermutigen, die zu einer wohlbegründeten Theorie zur Entstehung der Feenkreise führen kann. [Copyright &y& Elsevier]

Total or partial shading conditions have a significant impact rate on the capability of delivering energy, in addition to the on-site environmental condition which effects the PV module output production. Generally, the shading effect is caused by the PV generator inter-row configurations, cloudy perturbations, the buildings and trees. In this paper, an investigation study has been carried out by testing different PV module types (mono-crystalline, polycrystalline) under different shading rates. The obtained IV characteristics have been treated through the Bishop model where the power losses occurred on the PV module output, have been evaluated. The measured and estimated I-V characteristic plots illustrated a good agreement and the used model provides an accurate power losses prediction caused by different shading effects, even in desert areas. [ABSTRACT FROM AUTHOR]

Electricity generated using photovoltaic system can only be commercial if the photovoltaic modules operate reliably for 20–25 years under field conditions. Understanding the performance degradation of photovoltaic modules is critical for optimizing its financial viability. Performance degradation of photovoltaic modules is due to multiple factors such as installation site and module technologies. In order to gain insight on performance degradation of crystalline silicon PV technology in harsh environment, a degradation effects study of c-Si photovoltaic modules in desert environment was carried. The main contribution of this paper is focused on the evaluation of c-Si PV modules performance that operated in extreme environmental conditions. This evaluation usually consists of I-V curve field measurements and visual inspections. [ABSTRACT FROM AUTHOR]

In this paper, we examine the Early to Middle Holocene evolution of a prominent group of ground-water fed lakes in the southeastern hinterland of the Badain Jaran Desert (BJD) of northwest China. Specifically, we describe a sediment profile record from the Taoerlegetu (TR) palaeolake basin using multiple proxies of total organic carbon (TOC), total nitrogen (TN), C/N ratio, δ13C org , grain size and mineral composition based on a well-dated trench profile. As C/N values suggest that sedimentary organic matter mainly originated from aquatic plants, δ13Corg values can be used as a qualitative proxy for water level because aquatic plants in different biotopes (water depth) have different δ13C values. Our results show that from 10.9 to 9.1 cal kyr B.P., water level rose slowly, and aquatic macrophytes occupied the lake basin. From 9.1 to 5.5 cal kyr B.P., water level reached an even higher level and phytoplankton replaced macrophytes as the major contributor to organic matter. The humid episode of the lakes in the hinterland of the BJD in the early Holocene might be related to the increased groundwater supply from the northeast region of the Tibet Plateau. These findings are consistent with earlier studies of lacustrine and peat sediments found in periphery of the modern lake group, which indicate that their geographic extent may have been larger in the past. A relative drought period recorded in the studied succession from 8.5 to 8.0 cal kyr B.P. marks an interval of reduced ground-water transport from the Tibet Plateau. This interval probably corresponds to the "8.2 ka cold event" and provides evidence that this widespread climate episode influenced groundwater processes across inland Asia. • The δ13C org value could be used as a qualitative indicator for the change of water level. • Lakes in the hinterland of the Badain Jaran Desert shows different evolution progress with these in the edge. • The main water source of lakes in the hinterland of the BJD in the Early Holocene comes from the Tibet Plateau. [ABSTRACT FROM AUTHOR]

In this paper we aim to document the history of aeolian processes within the southern Sahara as part of the INQUA Dune Atlas. We review available luminescence ages for sand dunes across the southern Sahara to develop an improved understanding of the dune chronology on a regional basis and attempt to correlate periods of sand accumulation. This was achieved by analysing dune age by country, as well as by latitude and longitude. The results show a very patchy spatial distribution of dune ages with large gaps that encompass some of the largest sand seas. Despite these gaps, some related patterns in dune morphology and stratigraphy appear to be consistent between northern Nigeria and southern Mali where older linear dunes are distinct from younger Late Holocene transverse and barchanoid dunes. Elsewhere in Mauretania linear dunes with different orientations appear to have accumulated at different times, most likely in response to changes in atmospheric circulation. Regional climatic changes are identified where dunes are transgressed by lake deposits within endorehic basins. We identify four locations where dune accumulation is terminated by lacustrine transgressions, two of which, in Lake Chad and the Bodélé Depression, occur shortly after the last glacial maximum (LGM). The third example at Gobiero in Niger occurred later, in the early Holocene, around 8.4 ka and a fourth marks a later transgression of Palaeolake MegaChad after 4.7 ka. Larger-scale latitudinal and longitudinal distributions in dune ages across the southern Sahara do not show any consistent patterns, though this may be due to the small sample size relative to the study area. In addition, local variations in external controls such as wind regime, rainfall, vegetation and sand supply need to be considered, sometimes on a site by site basis. Limiting the analysis to dune ages determined using the single-aliquot regenerative-dose (SAR) protocol indicates a lack of dune preservation during the LGM and the Younger Dryas, times associated with increased dust input to the oceans which is assumed to indicate increased aeolian activity. The SAR dune dates suggest that preservation of dunes at the onset of succeeding humid intervals is an important component of the dune record. The most striking examples of this phenomenon occur where dunes are preserved within endorehic basins by lacustrine transgressions. [ABSTRACT FROM AUTHOR]

In this paper we describe measurements of the bidirectional reflectance-distribution function (BRDF) acquired over a 30-year period (1984–2014) by the National Aeronautics and Space Administration's (NASA's) Cloud Absorption Radiometer (CAR). Our BRDF database encompasses various natural surfaces that are representative of many land cover or ecosystem types found throughout the world. CAR's unique measurement geometry allows a comparison of measurements acquired from different satellite instruments with various geometrical configurations, none of which are capable of obtaining such a complete and nearly instantaneous BRDF. This database is therefore of great value in validating many satellite sensors and assessing corrections of reflectances for angular effects. These data can also be used to evaluate the ability of analytical models to reproduce the observed directional signatures, to develop BRDF models that are suitable for sub-kilometer-scale satellite observations over both homogeneous and heterogeneous landscape types, and to test future spaceborne sensors. All of these BRDF data are publicly available and accessible in hierarchical data format (http:car.gsfc. nasa.gov /). [ABSTRACT FROM AUTHOR]

Identifying provenance of aeolian deposits in the mid-latitude deserts of Asia is essential for understanding formation and changes of Earth surface processes due to palaeoclimatic fluctuations. While some earlier studies focused on the interpretation of palaeoenvironments on the basis of aeolian deposits mainly in the desert margins and inter-dune lacustrine sediments, research on provenance of desert sands in the vast Asian mid-latitude deserts is still rare. In this paper, we present new geochemical data which provide insight to the provenance of dune sands in the Badain Jaran Desert, northwestern China, an important part of this desert belt. We sampled aeolian and lacustrine sediments in various parts of the Badain Jaran Desert, and examined their major, trace and rare earth elements (REE) in bulk samples, coarse and fine fractions, respectively. In addition, we took and analyzed samples from a rarely known dune field with red sands, northeast of the Badain Jaran. Our results show that the sands from the Badain Jaran Desert are generally different from those in the red sand dune field in terms of REE pattern and geochemical characteristics, suggesting different sediment origins. Geochemical composition of the aeolian sand samples indicates these sediments should be mainly derived from mixed source rocks of granite, granitoids and granodiorite. Comparing the immobile trace elements and REE ratios of the samples from the Badain Jaran Desert, red sand dune field with rocks of granite, granitoids in their potential source areas, we conclude that: (1) The aeolian deposits in the Badain Jaran Desert are predominantly derived from the Qilian Mountains, northeastern Tibetan Plateau initially via fluvial processes; (2) The Altay Mountains and Mongolian Gobi are the ultimate source areas for the red sand dune field; (3) The Altai Mountains and Mongolian Gobi in the northwest, that could produce massive amounts of materials via intensive deflation and alluvial process, are additional sand sources of the Badain Jaran Desert although their contribution is of secondary significance. As the Badain Jaran Desert acts as sediment sinks of sediments from the Qilian Mountains of northeastern Tibetan Plateau via fluvial processes, it is likely that zircon grains of loess on the Chinese Loess Plateau with age distributions similar to those of the northern Tibetan Plateau could be derived from the Badain Jaran Desert, as the wind data suggest. [ABSTRACT FROM AUTHOR]

This paper aimed at identifying the most effective glazing type that suits different patient room layouts under desert clear skies. Year-round daylighting performance of three glazing types was compared with that of a 45 degree sun breaker for three different patient room layouts. Simulations were conducted for rooms facing south in Cairo, Egypt. The daylighting performance of the tested glazing types was less than that of a sun breaker. Electrochromic-60 and low E glazing were successful in the outboard bathroom design only, for large window sizes. The electrochromic-30 glass did not produce acceptable results in any of the tested cases. [ABSTRACT FROM AUTHOR]

Abstract: Compact settlements or —Ksur‖ have been commonly used in the hot dry climate of Algeria in response to imposed local environmental conditions through passive design strategies or means. These strategies include three major levels: settlement planning, building design and building components. A compact settlement provides a protective thermal environment and responds favorably to the harsh environmental stresses. It is built to withstand the excessive heat and mitigates the stresses imposed by the environment on people occupying outdoors and improves indoor comfort with minimum energy consumption. Although, there are now technical means that would allow building design to ignore the climate, there are still good reasons to adopt passive techniques, not only economic, but also to promote environmental sustainability at both local and global levels. This paper aims to give an overview and a comprehensive understanding of the compact city concepts and strategies to cope with the harsh conditions of the desert in a sustainable way. Recommendations and basic principles that may be of benefit in sustainable building and settlement design in the future are also discussed. Erreur ! Signet non défini. [Copyright &y& Elsevier]

Abstract: The paper reviews the dynamic relations between geology, soil mechanics, planning and construction in a desert environment. It claims that misunderstanding environmental processes, disregarding geological properties and climatic uncertainties, while planning for construction and development, can have decisive outcomes of potentially catastrophic implications, such as destabilizing the very terrain on which a project is built. To make this point, it reviews the evolution of a relatively small settlement located in the arid Negev Desert Highlands, Israel, and the way this has affected the very cliff on which it is built. [Copyright &y& Elsevier]

Abstract: In desert sunny clear-sky regions solar penetration can become excessive. This can cause non-uniform daylight distribution, glare and high solar heat gain, affecting both visual and thermal comfort. Shading devices, such as solar screens, were usually used to diffuse and prevent direct solar penetration into spaces. This paper investigates the impact of changing solar screen axial rotation angle and screen opening aspect ratio on daylighting performance in a typical residential living room space under the desert sunny clear-sky. The larger aim is to arrive at efficient solar screen designs that suit the different orientations. The study was divided into three consecutive phases. In phase one, the effect of the two parameters on Daylight Availability was tested. The solar screen was axially rotated by three different angles at 10° increments. Also, the aspect ratio of the screen opening in both horizontal and vertical directions was changed systematically. Simulation was conducted using the annual Daylight Dynamic Performance Metrics (DDPMs). In phase two, the Annual Daylight Glare Probability (DGP) metric was evaluated for the cases that were found adequate in phase one. In the third phase, the annual solar energy transmittance through the screen was calculated for the cases that achieved acceptable performance in the two previous phases in order to identify the more energy efficient screens. Solar screens with openings having horizontal aspect ratios were found to be the most effective, while those with vertical aspect ratios were achieved the lowest performance. In the North orientation, since almost all the cases that were tested in this research provided acceptable daylighting performance, the designer now have a variety of options to choose from. Preference should be given to screen openings of horizontal aspect ratios, especially the 12:1 and 18:1 (H:V) screens that achieved the best performance where 92% of the space was “daylit” in comparison with only 53% of the base case. In the East orientation, it is advisable to use the 12:1 (H:V) screen opening ratio, as it was found acceptable in the two daylighting testing phases and achieved the best performance in regards to annual transmittance of solar radiation. For the South orientation, there were also many acceptable choices. However, the 3:1 screen aspect ratio is recommended as it assists in saving energy by reducing the annual transmitted solar radiation (60% reduction) while achieving acceptable daylighting performance. [Copyright &y& Elsevier]

Abstract: In hot arid desert environments, the solar radiation passing through windows increases the cooling loads and the energy consumption of buildings. Shading of windows can reduce these loads. Unlike the woven solar screens, wooden solar screens have a thickness that provides selective shading properties. Perforated wooden solar screens were traditionally used for windows shading. Developing modern types of these shading systems can lead to significant energy savings. The paper addresses the influence of changing the perforation percentage and depth of these screens on the annual energy loads, hence defining the optimum depth/perforation configurations for various window orientations. Series of experiments were performed using the EnergyPlus simulation software for a typical residential building in the Kharga Oasis, located in the Egyptian desert. A range of perforation percentages and depths were tested. Conclusions prove that external fixed deep perforated solar screens could effectively achieve energy savings up to 30% of the total energy consumption in the West and South orientations. Optimum range of depths and perforation percentages were recommended. These are: 80–90% perforation rate and 1:1 depth/opening width ratio. These lighter and deeper solar screen configurations were found to be more efficient in energy consumption in comparison with the traditional ones. [Copyright &y& Elsevier]

Abstract: The desert climate is endowed by clear sky conditions, providing an excellent opportunity for optimum utilization of natural light in daylighting building indoor spaces. However, the sunny conditions of the desert skies, in countries like Egypt and Saudi Arabia, result in the admittance of direct solar radiation, which leads to thermal discomfort and the incidence of undesired glare. One type of shading systems that is used to permit daylight while controlling solar penetration is “Solar Screens”. Very little research work addressed different design aspects of external Solar Screens and their influence on daylighting performance, especially in desert conditions, although these screens proved their effectiveness in controlling solar radiation in traditional buildings throughout history. This paper reports on the outcomes of an investigation that studied the influence of perforation percentage of Solar Screens on daylighting performance in a typical residential living room of a building in a desert location. The objective was to identify minimum perforation percentage of screen openings that provides adequate illuminance levels in design-specific cases and all-year-round. Research work was divided into three stages. Stage one focused on the analysis of daylighting illuminance levels in specific dates and times, while the second stage was built on the results of the first stage, and addressed year round performance using Dynamic Daylight Performance Metrics (DDPMs). The third stage addressed the possibility of incidence of glare in specific cases where illuminance levels where found very high in some specific points during the analysis of first stage. The research examined the daylighting performance in an indoor space with a number of assumed fixed experimentation parameters that were chosen to represent the principal features of a typical residential living room located in a desert environment setting. Stage one experiments demonstrated that the screens fulfilled the requirements of the majority of tested cases. Illuminance levels in the examined residential space were satisfactory in 83% of the near zone cases and 53% in the mid-length zone, while the far zone suites 40% of the cases. Screen influence on daylighting was found to be very much dependent on the orientation of the window and time of the day. In stage two, the percentage of annual “Daylight Availability” was very much related to screen perforation percentage. As perforation percentage decreased, the percentage of Daylit and Over lit spaces decreased. At the same time, Partially Daylit areas of the space increased with similar percentages irrespective of the orientation. As a result of the twofold research stages, it is recommended to utilize a minimum of 80% perforation percentages for spaces similar to the tested case in the South orientation. In stage three, an initial investigation suggests that the use of screens can significantly reduce the occurrence of glare phenomena. Also, it is suggested to study the efficiency of designing Solar Screens that have non-uniform perforation ratios. These could prove useful in improving the illuminance levels in the mid-length and far zones of the unsatisfactory cases. In conclusion, minimum perforation percentages for Solar Screens were presented for specific design cases that encompassed different orientations, seasons and time of the day. In addition, a tool that could be used by architects for based on required annual “Daylit” areas for the design of Solar Screens that effectively achieve functional needs was provided. [Copyright &y& Elsevier]

Abstract: This paper reviews our current understanding of Quaternary climate and landscape changes in the desert areas of northern China, a key portion of the middle-latitude drylands on Earth. Combining earlier studies with our recent research and experience, we offer a comprehensive picture of the state of Chinese deserts during the Quaternary and, in the interest of enhancing future research, identify knowledge gaps and areas of uncertainty. Lacustrine deposits found over an area ranging from China’s western Taklamakan Desert to the eastern Hunshandake Sandy Lands suggest that extensive lakes occurred in China’s deserts during the Pleistocene. Analysis of digital elevation models from SRTM (Shuttle Radar Topography Mission) data supports this interpretation and shows the significant extent of these former lakes. New estimates of mean annual evaporation of ca. 1000 mm from lake surfaces and ca. 100 mm from land surfaces, confirms that local and regional rainfall is critical for maintenance of desert lakes in this temperate zone, especially during intervals when the mean annual rainfall is more than 100 mm. Rapid shifts between sand seas and lakes in geologically and environmentally diverse settings suggest that the drylands of China are very sensitive ephemeral systems, and not long-lasting as previously thought. Available chronologies suggest that there were large lakes in the western Taklamakan Desert and the Chadamu Basin during MIS (Marine Isotope Stage) 3, at ∼30 ka, probably related to a period of strong influence of northern hemispheric westerly winds. Channels and elevation models revealed by SRTM data and remains of lacustrine sediments also indicate that there was a large lake in the Hunshandake Sandy Lands in the eastern portion of the desert belt during the Quaternary. There is significant evidence that during the middle Holocene strong summer monsoons led to a relatively large increase in moisture availability in the entire desert belt of northern China. Lacustrine records from the Badain Jaran Desert in western Inner Mongolia suggest that it was generally dry before 10 cal ka, becoming wetter from 10 to 4 cal ka, and dry again afterwards. Study of palaeosols widely occurring in dune stratigraphy in the eastern portion of the desert belt, suggests that there was a period of wet and warm climate in this region during the mid-Holocene Optimum, at a minimum between 6 ka and 4 ka, but possibly lasting longer. Recent observations dealing with the generation and transport of dust from Central Asia indicate that the causal relationship between sand seas and loess sequences is not as close as previously assumed. These results suggest that there is an urgent need to examine whether the frequency and amplitude of climatic variation in Chinese deserts are somehow similar to that having occurred in the Sahara Desert of North Africa. Deserts in northern China were also important focal regions for Neolithic cultures during intervals when environmental conditions supported a denser vegetative cover. There is evidence that some areas of woody vegetation to the west of Badain Jaran Desert were deforested by humans by ca. 4000 yr B P, although it is still debatable whether humans have had a significant impact in other areas at that time. Opinions on the severity of desertification vary and are sometimes contradictory due to the lack of long-term, field-based, investigations. [Copyright &y& Elsevier]

Abstract: Based on samples taken from four large sand seas of northern China, this paper first provides basic data about the concentrations and chemistries of soluble salts in deserts of northern China and then discusses the origins and parameters triggering geographical variations. The total concentration of soluble salts in the aeolian sands of four large sand seas in northern China ranges between 0.14‰ and 1.32‰, with the pH of the soluble salts solution (mixing ratio of sand and water 1:5) changing between 8.4 and 9.6, confirming alkaline soil conditions in these regions. Sodium chloride and bicarbonate are the dominant salts occurring as soluble salts in the aeolian deposits of these sand seas. The geographical changes of soluble salts'' concentration display a clear correlation with regional climatic parameters, i.e., precipitation and temperature. The domination of sedimentation of soluble salts in the aeolian sands deposited via atmospheric processes is discussed, which are heavily associated with dry deposition. The mean percentages of Na and Cl, derived from dry depositions, are estimated to be >90% in both Badain Jaran and Taklamakan deserts. [Copyright &y& Elsevier]

Abstract: In recent years, the Populus euphratica Oliv population has shown signs of degradation that are hypothesized to reflect decreases in surface water. Based on the analysis of tree-ring data and field inventories for P. euphratica populations in 14 study sites in the lower reach of the Heihe River, China, this paper assesses (1) age–height growth relationships, (2) tree growth levels, and (3) effects of stand type, soil type, water condition and river runoff on rate of change in tree height growth. There is a close relationship between tree height and age in P. euphratica, but the extent of this relationship varies at different growth stages and at different locations in the lower reach of the Heihe River. In this area, most of the natural P. euphratica forest is currently at a suppressed growth level with an unfavorable growing condition. The height growth in particular appears to be quite sensitive and variable in terms influences of internal and external factors over the tree lifespan, with changes in the water–soil conditions, wind action and gravity being particularly detrimental. In general, tree height growth rate was higher when growth conditions were favorable than in poorer growth conditions; however, the actual differences in growth between trees in the same area was more variable under good growth conditions and could be less variable for trees growing in poor conditions. In addition, the correlation between P. euphratica height growth and river runoff was not significant. These findings should be helpful in determining forestry management measures for the sustainable development and maintenance of natural P. euphratica forests in this study area and for overall environmental evaluation and monitoring of ecosystems of inland river basins of arid areas. [Copyright &y& Elsevier]

Abstract: Fog has been studied in the Atacama Desert of Chile for the past ten years. This paper analyzes its temporal and spatial variability, relying in part on satellite images (GOES) to analyze the frequent orographic fog and the low cloud deck (stratocumulus, Sc) that generates advective fog in the area. Fog water fluxes were measured with Standard Fog Collectors (SFC). Field trips and observers provided information on cloud top and base and the presence of fog. Vegetation in fog oases were used to confirm the results of these surveys. The Sc moves onshore into the continent with different intensities depending on season and time of day. The maximum spatial extent occurs during winter and at night. Fog is frequent in the coastal cliffs, where fog water fluxes of 7.0 L m−2 day−1 were measured using a SFC. It is less frequent 12 km inland, where the collection rates were less than 1 L m−2 day−1. The height of the fog collector above the ground affected the collection rate. The highest fog water fluxes were recorded at Alto Patache at altitudes of between 750 and 850 m a.s.l. The growth or thickness of the cloud is important in the collection of fog water. The information that GOES provides on the altitude of the top of low clouds is used to analyze this factor. Fog oases are described and analyzed in relation to how the geographical location of fog influences the growth of vegetation. [Copyright &y& Elsevier]

Abstract: Knowledge about changes of regional carbon density during late Quaternary is of great significance for understanding regional and global carbon cycles. Taking the Hunshandake Sandy Land, located in eastern Inner Mongolia of China as an example, this paper aims to reconstruct Late Quaternary environmental changes, and then to discuss the fluctuations of organic carbon density and storage in the desert environment of northern China. The study area with a mean annual precipitation ca. 300 mm is characterized by the occurrence of fixed and semi-fixed sand dunes reaching a maximal height of 30 m. The research methods included field observations, examinations of grain sizes, as well as carbon and calcium carbonate contents of the sediment samples. The chronology is based on Optically Stimulated Luminescence (OSL) dating and radiocarbon analyses. This work reveals that the organic carbon density in the surface layer of the Hunshandake Sandy Land changed between at least 2500 g/m2 during the Holocene Climatic Optimum and 1500 g/m2 when aeolian processes dominate. The dune construction was restricted by periglacial processes during the Last Glacial Maximum (LGM). The Holocene Climatic Optimum, indicated by extensive formation of kastanozem soils, occurred between 5 ka and 3 ka in the study area. Although desertification might cause a 40% loss of total organic carbon storage within several dozen of years in the study area, a considerable amount of this carbon was re-deposited in the regions of downwind directions. [Copyright &y& Elsevier]

Microbial crusts are attracting much interest in view of their possible uses in environmental conservation and ecological restoration of the arid and semiarid regions. Because algae play an irreplaceable important role in the early formation and the strengthening of microbial crusts, they are paid much more attention to than other cryptogams. In this paper, an overview of the current knowledge on the fine structure and development of microbial crust, focusing on the algal biomass, vertical distribution, succession, influential factors on algae, cohesion of soil stabilization, cementing mechanism for soil particles and the microalgal extracellular polymers is given, with particular emphasis on the authors' researches, and some prospects are put forward as well. [ABSTRACT FROM AUTHOR]

This paper presents first, a brief over-view of research activities in the Landscape Architecture Program at the University of Arizona. Included is both the pedagogical foundation for the research emphasis and a brief summary of research topics pursued by faculty and graduate students during the past 15 years. The second and major part of thepaper summarizes selected components of a long-term research projectin which graduate students in Landscape Architecture and Renewable Natural Resources Studies played significant roles. Primary emphasis is on riparian landscapes located in southeastern Arizona. The research was developed in three phases. First was an exploration of people-landscape relationships via open-ended interviews; second, was survey research to explore perceptions of landscape values and attitudes about appropriate uses for these landscapes; and third, was the assessment of landscape change, both perceived and physical, in the same landscapes. Together, the three phases span 15 years, from 1981 to 1996. Case studies of two riparian areas that represent diverse contextual settings are discussed. (C) 1998 Elsevier Science B.V. [ABSTRACT FROM AUTHOR]