Region Of Northwestern China Research Articles

Dual origins of the Northwest Chinese Kyrgyz: the admixture of Bronze age Siberian and Medieval Niru'un Mongolian Y chromosomes.

The Kyrgyz are a trans-border ethnic group, mainly living in Kyrgyzstan. Previous genetic investigations of Central Asian populations have repeatedly investigated the Central Asian Kyrgyz. However, from the standpoint of human evolution and genetic diversity, Northwest Chinese Kyrgyz is one of the more poorly studied populations. In this study, we analyzed the non-recombining portion of the Y-chromosome from 298 male Kyrgyz samples from Xinjiang Uygur Autonomous Region in northwestern China, using a high-resolution analysis of 108 biallelic markers and 17 or 24 STRs. First, via a Y-SNP-based PCA plot, Northwest Chinese Kyrgyz tended to cluster with other Kyrgyz population and are located in the West Asian and Central Asian group. Second, we found that the Northwest Chinese Kyrgyz display a high proportion of Y-lineage R1a1a1b2a2a-Z2125, related to Bronze Age Siberian, and followed by Y-lineage C2b1a3a1-F3796, related to Medieval Niru'un Mongols, such as Uissun tribe from Kazakhs. In these two dominant lineages, two unique recent descent clusters have been detected via NETWORK analysis, respectively, but they have nearly the same TMRCA ages (about 13th-14th centuries). This finding once again shows that the expansions of Mongol Empire had a striking effect on the Central Asian gene pool.

Storage Period and Different Abiotic Factors Regulate Seed Germination of Two Apocynum Species - Cash Crops in Arid Saline Regions in the Northwestern China.

On degraded land in arid regions, cultivation of Apocynum species can provide significant environmental benefits by preventing soil erosion and desertification. Furthermore, Apocynum venetum and Apocynum pictum, which are mainly distributed in salt-barren lands in the northwestern region of China, are traditionally used to produce natural fiber and herbal tea. Direct sowing of both species may encounter various abiotic stresses such as drought and salinity. However, these effects on germination remain largely unknown, especially for seeds with different storage periods. The aim of this study was to evaluate the effects of storage period, light condition, temperature regime, drought, and salinity on germination performances of both species. Germination experiment was carried out in November 2017. There were four replicates for each treatment, and each petri dish contained 25 seeds. The results indicated that prolongation of storage period significantly decreased the germination percentage and velocity, especially under abiotic stresses. Light did not affect seed germination of A. venetum and A. pictum under any conditions. Seeds had better germination performance at 10/25 and 15/30°C than those of seeds incubated at any other temperatures. With the increase of polyethylene glycol (PEG) and salinity concentrations, seed germination for both species gradually decreased, especially for seeds stored for 2 years. Low PEG (0–20%) and salinity concentration (0–200 mM) did not significantly affect germination percentage of freshly matured seeds. However, long-time storage significantly decreased drought and salinity tolerance in A. venetum and A. pictum during germination stage. For saline soils in arid and semi-arid regions, freshly matured seeds or 1-year-stored seeds of both Apocynum species are recommended to be sown by using drip-irrigation in spring.

Drivers of carbon flux in drip irrigation maize fields in northwest China

BackgroundUnder the escalating threat to sustainable development from the global increase in carbon dioxide concentrations, the variations in carbon flux in the farmland ecosystem and their influencing factors have attracted global attention. Over the past few decades, with the development of eddy covariance technology, the carbon fluxes of farmlands have been determined in many countries. However, studies are very limited for drip irrigation maize the arid regions in northwestern China, which covers a large area where a mixed mode of agriculture and grazing is practiced.ResultsTo study the effects of drip irrigation on the net ecosystem productivity (NEE), ecosystem respiration (ER), gross primary production (GPP) and net biome productivity (NBP) in the arid regions of northwestern China, we measured the carbon flux annually from 2014 to 2018 using an eddy covariance system. Our results showed that the maize field carbon flux exhibited single-peak seasonal patterns during the growing seasons. During 2014–2018, the NEE, ER and GPP of the drip-irrigated maize field ranged between − 407 ~ − 729 g C m−2, 485.46 ~ 975.46 g C m−2, and 1068.23 ~ 1705.30 g C m−2. In four of the 5 study years, the ER released back to the atmosphere was just over half of the carbon fixed by photosynthesis. The mean daily NEE, ER and GPP were significantly correlated with the net radiation (Rn), air temperature (Ta), leaf area index (LAI) and soil moisture (SWC). The results of path analysis showed that leaf area index is the main driving force of seasonal variation of carbon flux. When harvested removals were considered, the annual NBP was − 234 g C m−2, and the drip-irrigated maize field was a carbon source.ConclusionsThis study shows the variation and influencing factors of NEE, ER and GPP in the growth period of spring maize under film drip irrigation in arid areas of northwest China. The ecosystem was a carbon sink before maize harvest, but it was converted into a carbon source considering the carbon emissions after harvest. The variation of carbon flux was influenced by both environmental and vegetation factors, and its leaf area index was the main driver that affects the seasonal variation of carbon flux.

Near‐Surface Warming Reduces Dew Frequency in China

AbstractLong‐term (1961–2010) observations of dew data collected at 597 stations over China show that dew frequency decreased by 5.2 days per decade due primarily to near‐surface warming and associated decreases in relative humidity (RH). Moreover, the percentage decreasing rate of dew frequency in arid regions (precipitation PR <400 mm yr−1) are larger than that in humid regions (PR ≥800 mm yr−1). Compared with the 1960s, the mean dew frequency in the 2000s decreased by 28%, 40%, 50% in humid, semihumid (400 ≤ PR < 800 mm yr−1), and arid regions, respectively. Surface warming is larger in arid regions in northwestern China than its humid and semihumid regions during recent global warming, which leads to larger decreases in surface RH and makes dew events less likely. Since dew contributes significantly to surface water balance in arid regions, the large decreases in dew frequency may contribute to “the drier getting drier” response to global warming over arid regions.

Quantifying spatio-temporal variations of evapotranspiration over a heterogeneous terrain in the Arid regions of Northwestern China.

ABSTRACT Evapotranspiration (ET) is a major component of water and energy budgets in terrestrial ecosystems and quantifying ET over a heterogeneous land surface is of extraordinary significance. However, previous studies on the spatial distribution of daily ET in the middle Hexi corridors were mostly temporal discontinuous, and thus hinder the applications in agriculture and meteorology. Based on Land Remote-Sensing Satellite (Landsat) 8 Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS) data and the Surface Energy Balance System (SEBS) model, surface ET in 2014 were estimated over a desert oasis with heterogeneous land cover in the middle Hexi corridors of the arid regions in northwestern China. Daily ET was derived from the reference crop ET which was based on the relationship between actual ET and potential ET. The main results indicated that (1) the estimated daily ET values agreed well with the Eddy Covariance (EC) measurements for cropland (The coefficient of determination (R 2) = 0.96, p < 0.05, Root Mean Square Error (RMSE) = 1.32 mm day−1, Mean Absolute Error (MAE) = 1.11 mm day−1). Daily ET was more than 2.5 mm day−1 from June to July in 2014. (2) Seasonal ET was the largest in the summer (190.55 mm), followed by spring (100.03 mm), autumn (62.27 mm), and winter (6.83 mm). (3) ET from the waterbody was the highest, followed by ET from cropland, shelterbelt, bare land, and shrubland, suggesting that ET was mainly controlled by the water availability of the underlying surface. Multiple land-cover types showed similar variations in a year, but the seasonal variations were different. This study provides a foundational understanding of the patterns of water and heat exchange over heterogeneous regions, which can be helpful to make local policy in rational water management and land resource utilization.

A study on sediment avoidance diversion and the coordinated dispatch of water and sediment at an injection-water supply project on a sediment-laden river

ABSTRACT Rivers in the north-western region of China have a high sediment content, and the construction of reservoirs on these rivers must address the problem of sedimentation that results in a loss of reservoir capacity. In this study, the YZD (Yazidang) reservoir was considered as a typical case, to address the problem of sedimentation in injection-type water supply reservoirs in Northwest China. The temporal and spatial characteristics of the sediment in this water diversion project were analyzed based on available 46-year water and sediment data. The concept of ‘sediment avoidance diversion’ was proposed, which reduces the entry of sediment into the reservoir. A one-dimensional numerical model for water-sediment coupling was established, and the characteristics of water-sediment erosion and deposition for different operational modes were analyzed. The results show that during a period of high sediment content, large-scale siltation occurs in a water diversion channel. To alleviate sediment deposition in a diversion channel, two control strategies for mitigating siltation were formulated. Considering the pros and cons of these control strategies, a reasonable water-sediment joint operation plan has been proposed to extend the service life of the YZD reservoir. This research provides a theoretical basis for sedimentation treatment and control of similar reservoirs.

Evaluation of water resources carrying capacity of major industries in northwest of China: A case study of textile industry in Aksu, Xinjiang Province, China

With the implementation of the “Belt and Road Initiative”, the north-western region of China is welcoming a new development opportunity. Textile industry is a vital industry for people’s livelihood in Xinjiang, which plays an important role in promoting the development of related industries, stimulating the growth of domestic demand, increasing the capacity and level of employment, and promoting social harmony. However, the spatial and temporal distribution of water resources in Xinjiang is extremely uneven, the contradiction between water resources shortage with economic and social development is increasingly prominent. This paper aims to figure out the pressure degree on water resources with the development of textile industry, propose the countermeasures of water saving and pollution reduction in textile industry, by using the osculating value method model to evaluate the water resources carrying capacity (WRCC) of Aksu’s textile industry. Results indicates that the water resources carrying capacity in the study area was overload in 2015, the water consumption of textile industry and the agricultural irrigation were the dominant factors caused a situation of an overloaded water resources carrying capacity. Beside government issues policies to limit water resources consumption and sewage permit system, the optimal measure for reversing this situation is to adopt advanced technologies in water conservation and pollution control in textile industry and new water-saving technology of agriculture irrigation.

High concentrations of sodium and chloride ions have opposing effects on the growth of the xerophyte Pugionium cornutum under saline conditions

AbstractBackground: The research on plant salt tolerance has mainly focused on Na+, but Cl− has been relatively neglected. Previous studies have found that the xerophyte Pugionium cornutum, an important forage grass in the arid and semi‐arid regions of northwestern China, could synergistically accumulate high quintiles of Na+ and Cl− in its shoots under NaCl treatments. However, the separate effects of these ions on the adaptation of P. cornutum to saline conditions have not been investigated.Aims: In this study, the response of P. cornutum to Na+ and Cl− was analyzed.Methods: Four‐week‐old seedlings were treated with additional 50 mM NaCl, Na+‐specific solution containing 50 mM Na+ with a mix of , H2 , and as counter anions, and Cl−‐specific solution containing 50 mM Cl− with a mix of K+, Ca2+, and Mg2+ as counter cations.Results: Compared with the normal growth condition irrigated with Hoagland solution, the Na+‐specific solution severely impaired the growth and photosynthesis of P. cornutum due to the high accumulation of Na+ in shoots and the deterioration of tissue K+ homeostasis; while the Cl−‐specific solution significantly increased shoot fresh and dry biomass. The Cl−‐specific solution could also increase the turgor pressure in leaves for enhancing osmotic adjustment, which should be mainly attributed to the large accumulation of Cl−, since the concentrations of other ions, including K+, Mg2+, Ca2+, H2 , and , in tissues under Cl−‐specific treatment were maintained at the same levels as those observed under the normal condition.Conclusions: P. cornutum displays an excellent tolerance to moderate Cl− but not to Na+, and the large accumulation of Cl− should play a positive role in stimulating the growth of P. cornutum under salt stress.

Measuring and modeling evapotranspiration of a Populus euphratica forest in northwestern China

Vegetation is sparsely distributed in the arid regions of northwestern China, and accurately measuring and partitioning of evapotranspiration is of importance for ecosystems in such areas. In this study, we measured and analyzed diurnal and phenological variations in evapotranspiration using the eddy–covariance method based on the Penman–Monteith, Priestley–Taylor, Shuttleworth–Wallace models, a newly proposed improved dual source model and a clumped model in a forest reserve in the Ejin oasis of Populus euphratica in 2015 and 2016 growing seasons. A sensitivity analysis was performed for the models with higher accuracies and we examined the biotic and abiotic controls on evapotranspiration. The results show that the total amounts of evapotranspiration during the two growing seasons in 2015 and 2016 were 622 and 612 mm, respectively. Phenological variations in evapotranspiration produced single-peak curves, while diurnal variations reflected the influence of high temperatures on some afternoons. The Priestley–Taylor and the improved dual source models gave the most accurate evapotranspiration values at the daily scale and appeared to be most suitable for the estimation of evapotranspiration for the species in arid regions. In addition, both models were the most sensitive to net radiation (Rn).

Soil Salinity and Moisture Control the Processes of Soil Nitrification and Denitrification in a Riparian Wetlands in an Extremely Arid Regions in Northwestern China

Soil nitrification and denitrification are key nitrogen (N) removal processes in riparian wetlands in extremely arid regions, but the driving factors of the two N processes in these wetlands are still unclear. We measured soil nitrification and denitrification rates and related environmental properties in a typical riparian wetland in the middle reaches of the Heihe River, northwestern China. Our results showed that rates of soil nitrification and denitrification exhibited moderate variability, ranging from 52.77 to 221.18 μg kg−1 h−1 and 91.25 to 428.26 μg kg−1 h−1, respectively. Soil salinity was high, with mean electrical conductivity (EC) of 6.8 mS cm−1. Soil salinity and moisture were the key factors influencing nitrification and denitrification in this riparian wetland in an extremely arid region. Soil salinity exerted significant inhibitory impact on soil nitrification when EC was &gt; 4.05 mS cm−1. Soil nitrification increased with an increase in soil moisture when soil water content &lt; 27.03% and decreased with an increase in soil moisture when soil water content &gt; 27.03%. Denitrification had a significantly negative relationship with soil salinity, and significantly positive relationship with soil moisture. The interaction of soil salinity and moisture played a central role in regulating soil denitrification. Based on these results, we propose that water consumption of riparian wetlands, and the planting of halophytes, should be increased to reduce soil salinity and increase soil moisture, which is essential for sustaining soil N removal function in riparian wetlands in extremely arid regions.

SPM control on the partitioning and balance of 210Po and 210Pb in high-turbidity surface waters of the East China Sea

210Po and 210Pb are well-known tracer pairs for some biomass and chemical processes in the marine system. In this study, 210Po and 210Pb were analyzed in surface seawater collected from the East China Sea (ECS), in atmospheric deposition, and in riverine input water collected along the ECS coast. The atmospheric fallouts of 210Po and 210Pb were higher in the dry season, due to the arrival of storm dust from the northwestern region of China. In the riverine input water, the particulate 210Po and 210Pb dominated (corresponding to 33–94% and 50–92% of the total, respectively), especially during the flood season. In the surface seawaters, the percentage of particulate 210Po (17–85%) was generally greater than that of 210Pb (10–76%). Additionally, in the Changjiang Estuary, log Kd(Po) and log Kd(Pb) were negatively correlated with log suspended particulate matter (SPM) (R = 0.71, P = 0.013 for Po, R = 0.67, P = 0.019 for Pb). 210Pb showed a stronger “particle effect” than 210Po when SPM <1.00 mg L−1, and vice versa when SPM >1.00 mg L−1. The deficit of 210Po relative to 210Pb gradually decreased from the Changjiang Diluted Water, to the Shelf Merged Water and the Taiwan Warm Current Water. The mass balance of 210Po and 210Pb in the water column of the estuary indicated that the Changjiang River was the dominating input source (providing 91% and 88% of the 210Po and 210Pb, respectively); meanwhile, the shelf export was the dominating output source (accounting for 68% and 78% of the 210Po and 210Pb, respectively).

Morphology and microstructure of Pellites hamiensis nov. sp., a Middle Jurassic liverwort from northwestern China and its evolutionary significance

Pelliales is a basal lineage of the simple thalloid liverworts. Here, we describe a simple thalloid liverwort from the Middle Jurassic Xishanyao Formation of the Turpan–Hami Basin, Xinjiang Uygur Autonomous Region in northwestern China. The thalloid fossil liverwort is described as a new species: Pellites hamiensis (Pelliaceae, Pelliales). Pellites hamiensis nov. sp. resembles the extant species of Pelliaceae in having ribbon-like segments, conspicuous costae that appear as ridges on the ventral surface, rectangular cells with thickened walls adjacent to the margin, and elongated cells in the middle part of the thallus. The occurrence of P. hamiensis nov. sp. extends the fossil records of Pellites back to the Aalenian-Bajocian or Bajocian (ca. 170 Ma) and suggests that the divergence time of the Pelliaceae is no later than the Middle Jurassic.

Moisture changes over the past 467 years in the central Hexi Corridor, northwestern China

The long-term characteristics of precipitation in arid and semi-arid areas are of great interest because these areas are very sensitive to climate change and human activities. The Hexi Corridor is an arid and semi-arid region in northwestern China that also is an important sector of the Silk Road Economic Belt; despite the region’s dependence on precipitation, annually resolved, long-term moisture records are still lacking for this region. Here, a standard tree-ring width chronology spanning 1484–2015 AD is developed for the Hexi Corridor using Qilian juniper (S. przewalskii Kom.). The chronology is used to reconstruct moisture changes in the region over the past 467 years. Correlation analyses indicate that the tree-ring width index has a significant positive correlation with the June SPEI (standardized precipitation evapotranspiration index) on a twelve-month time scale (r=0.73, n=65, p<0.001). We used this information to build a transfer function that explains 52.5% of the variance in the SPEI reconstructed for the period from 1549 CE to 2015 CE. Our study area experienced clear alternations between dry and wet periods. Especially long wet periods include 1600–1650 AD and 1762–1804 AD; long dry periods include 1670–1693 AD, 1917–1970 AD, and 1990–2015 AD. The 1920s was the most severe period of drought in the last 467 years. The results of wavelet analysis and running correlation analysis indicate that the atmospheric circulation system experienced a notable shift around the 1800s, after which point the role of the westerly system grew more pronounced.

Analysis of the potential of reclaimed water utilization in typical inland cities in northwest China via system dynamics

Located in the hinterland of the Eurasian continent, the inland areas of northwestern China have an arid climate and are confronted with continuing challenges in water resources quantity and quality. Reclaimed water plays an important role in maintaining the sustainable use of urban water resources, especially in arid regions. In this paper, a system dynamics urban reclaimed water model (SDURWM) considering the status of arid regions in northwestern China was constructed. The supply and demand balance index (RWB) and the utilization efficiency index (RWUE) of reclaimed water were proposed as evaluation indicators. The potential of reclaimed water utilization (2016–2025) in three typical cities with similar natural environments and population sizes but with large economic differences were estimated by the SD model. Then the relevant values of reclaimed water quota, supply and resident awareness were adjusted within the range of 10%–20%. The predicted results from intervention demonstrate that the RWB of three cities will be closer or maintain to the ideal value, and that the RWUE will increase by about 0.1, compared with the non-intervention results. This indicates that a minor change of the targeted policies can invigorate the capacity of reclaimed water use in droughty cities. This paper provides some effective solutions for the government's planning of developing the potential of reclaimed water.

Mining Subsidence Prediction by Combining Support Vector Machine Regression and Interferometric Synthetic Aperture Radar Data

Mining subsidence is time-dependent and highly nonlinear, especially in the Loess Plateau region in Northwestern China. As a consequence, and mainly in building agglomerations, the structures can be damaged severely during or after underground extraction, with risks to human life. In this paper, we propose an approach based on a combination of a differential interferometric synthetic aperture radar (DInSAR) technique and a support vector machine (SVM) regression algorithm optimized by grid search (GS-SVR) to predict mining subsidence in a timely and cost-efficient manner. We consider five Advanced Land Observing Satellite (ALOS)/Phased Array type L-band Synthetic Aperture Radar (PALSAR) images encompassing the Dafosi coal mine area in Binxian and Changwu counties, Shaanxi Province. The results show that the subsidence predicted by the proposed InSAR and GS-SVR approach is consistent with the Global Positioning System (GPS) measurements. The maximum absolute errors are less than 3.1 cm and the maximum relative errors are less than 14%. The proposed approach combining DInSAR with GS-SVR technology can predict mining subsidence on the Loess Plateau of China with a high level of accuracy. This research may also help to provide disaster warnings.

Rethinking vulnerability and human behaviour in arid and semi-arid regions in northwestern China.

The relationship between human behaviour and vulnerability is interactive, especially in arid and semi-arid regions. This paper analyses vulnerability and human behaviour in the core areas of Qilian Mountains National Park, which is located in Qilian and Sunan counties. We used the vulnerability index and grey correlation degree methods to analyse the data. The results show that from 2005 to 2017, the vulnerability degree in the Qilian Mountain area decreased gradually (Qilian County vulnerability decreased from 0.0357 to - 0.2237, and Sunan County vulnerability decreased from 0.1428 to - 0.4489). In 2017, the degree had reached its lowest value due to central and local government policy (- 0.2237 and - 0.4489). Considering that human behaviour contributed to the vulnerability degree, we find that land use and agricultural development mode, the acceleration of industrialisation and changes in the spatial patterns of human activities, and the development of urbanization and changes in resident identities are the main concepts driving the relationship between human behaviour and vulnerability. The innovative assessment indicators developed in this study can be applied to thoroughly explore the relationship between human behaviour and vulnerability and to find the influencing factors. Under certain conditions, this approach can be applied to vulnerability research in specific countries and regions.

Looking for asymmetries and nonlinearities: The nexus between renewable energy and environmental degradation in the Northwestern provinces of China

Recent industrial surge in the Northwestern provinces of China resulted in substantial energy consumption and adverse effect on the environment. Despite being less established, the Northwestern region of China has strategic importance and the use of renewable energy can potentially promote sustainable development in this region. Considering this aspect, this study aims to investigate the impact of renewable energy on environmental pollution in five Northwestern provinces of China during 1995–2014. This study uses the Nonlinear Autoregressive Distributed Lag bounds testing approach with the structural break unit root and other specifications tests. The results indicate that renewable energy positive shock has an adverse impact on the CO2 emissions of the Northwestern provinces of China. The effect of renewable energy use varies in five provinces, i.e. it is more significant in Gansu, Qinghai and Xinjiang than in Ningxia and Shaanxi. However, reduction in renewable energy consumption leads to higher level of CO2 emissions and this effect is more significant for Ningxia and Shaanxi in the long run. Furthermore, the positive shockwaves in nonrenewable energy, GDP and transportation are associated with environmental pollution in these provinces both in short run and long run. Nevertheless, the impact of negative shockwaves in nonrenewable energy consumption on environmental pollution is more significant than economic development for all provinces. Our findings suggest that: cutting down fossil fuels use can substantially improve environmental quality in these provinces; depending on the provincial geographies and government strategies, the intensity of positive impact of renewable energy towards CO2 emissions reduction differs among five provinces. Likewise, renewable energy development has abundant potential to increase the economic and ecological sustainability in the Northwestern provinces of China in the long run.

A fuzzy‐based multi‐objective robust optimization model for a regional hybrid energy system considering uncertainty

AbstractRegional hybrid energy system (RHES) is an effective way to accommodate clean energy and reduce its uncertainty. It is also an important development direction for energy market reform, playing an important role in the field of energy supply and demand. Based on electricity price, thermal price, and the relationship between load supply and demand, the paper proposes an optimal scheduling model for regional energy systems to promote clean energy consumption. Firstly, the typical structure and system modules of the integrated regional energy system are introduced in detail, and the two subsystem operating models of electricity and heating are given. Secondly, a multi‐objective function that combines the economics and stability of the system is constructed. The model maximizes the economic benefits and minimizes the net load fluctuations on the basis of maximizing the consumption of clean energy. The multi‐objective singularity is realized by fuzzy membership function. The decision‐making risk caused by the uncertainty of clean energy output is analyzed by introducing robust optimization theory. Finally, the effectiveness of the proposed model is verified based on a region in northwestern China. The results show that the proposed multi‐objective model can combine different optimization demands together, maximize the economic characteristics of clean energy while properly controlling risks, and provide reasonable support for decision makers to develop optimal operation plans.

Shallow foehn on the northern leeside of Tianshan Mountains and its influence on atmospheric boundary layer over Urumqi, China — A climatological study

Abstract The climatology of shallow foehn, also known locally as elevated south-easterly gales (ESEGs), on the northern lee side of the central Tianshan Mountains is analysed using radiosonde data recorded over a period of 10 years at Urumqi, the capital of Xinjiang Uygur Autonomous Region in north-western China. ESEGs are a frequent weather phenomenon in the region, occurring on average 128.5 days/yr and most often in winter (47.0 days), particularly January (17.5 days), and least in summer (18 days). The vertical ESEG structures also undergo seasonal variations, with the height of the maximum ESEG wind and the base and top of the ESEG layer more elevated in the warm half (late spring through early fall) of the year than the cold half. However, the monthly mean maximum wind speeds, which vary around 10 m/s, appear to be independent of season. A typical synoptic pattern accompanying ESEGs is characterized by opposite air masses to the east (cold) and west (warm) of Xinjiang. A strong low-level west-east pressure gradient helps push cold air to enter Xinjiang from the east, which subsequently induces a north-south pressure gradient across the Tianshan Mountains. This regional pressure gradient combined with terrain channelling leads to the development of ESEGs. A comparison of boundary layer structure between days with/without ESEGs in winter shows that the ESEG days are accompanied by deeper (average of 900 m) and more intense (average 6 °C) inversion, but there is little difference in the cold air pool Froude Number between the two types of days.

Climate changes in the Qaidam Basin in NW China over the past 40 kyr

Little is known about the climate and environmental changes that have occurred in the extremely arid regions of China since MIS (Marine Isotope Stage) 3 (59–29 cal kyr BP), when most regions in northwestern China and the Tibetan Plateau featured warm and humid conditions. In this paper, we present a record of the climate changes in the Qaidam Basin in arid northwestern China over the past 40 kyr based on the mineralogy of a 35-m-long sediment core recovered from Qarhan Salt Lake. Our results show that the lake was a saline or hyper-saline lake saturated with respect to gypsum between 40 and 33 cal kyr BP. Beginning at 33 cal kyr BP, evaporite formation was dominated by halite precipitation, indicating that the lake salinity had increased extensively and that the climate became drier during 33–24.5 cal kyr BP. The lake salinity then increased continuously, resulting in the appearance of bischofite between 24.5 and 14.6 cal kyr BP. The disappearance of bischofite and the increase in gypsum indicate that the salinity of the water decreased slightly between 14.6 and 8.3cal kyr BP. However, during the last 8300 years, the lake has dried up and is now a playa. Generally, the climate was wet in late MIS 3, arid in MIS 2 (29–11.7 cal kyr BP), and hyperarid in the Holocene. The relatively humid conditions may have resulted from weak evaporation caused by the relatively low insolation and intense ice-albedo feedback in late MIS 3. The decreased insolation and dramatically increased Eurasian ice volume in MIS 2 may have led to limited precipitation, which resulted in persistent dry climate conditions in the Qaidam Basin. In the Holocene, the reduction in ice volume reduced the albedo, and this change, in conjunction with increased insolation, may have led to evaporation exceeding local precipitation, resulting in hyperarid climate conditions in the Qaidam Basin.