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Anthropogenic Influences on Heavy Precipitation during the 2019 Extremely Wet Rainy Season in Southern China
No full textAnthropogenic forcings have reduced the likelihood of heavy precipitation in southern China like the 2019 March-July event by about 60
Numerical simulation of the effects of canopy properties on airflow and pollutant dispersion in street canyons
No full textThe air flow and pollutant concentration fields in a street canyon affected by trees could affect the comfort and health of residents. At present, the description of the non-uniform/discontinuous distribution of leaves is difficult. In this study, the leaf distribution in the canopy was characterized by establishing non-continuous (uniform/random) algorithm based on a numerical simulation method, and the effects of canopy properties including, height, porosity and uniform/random leaf distribution, on the airflow and pollutant concentration fields in urban street canyons were investigated. The position of the tree canopy was found to directly affect the airflow field form and the air velocity distribution in the street canyon at low inflows. The average air velocity in the street canyon could be reduced significantly when the top of the tree canopy is near the top of the street canyon. The air velocity and pollutant concentration in the street canyon would vary only slightly due to the canopy porosity. Due to the increasing canopy porosity, the air velocity would increase, and the pollutant concentration would be reduced. The leaves are non-continuous and uniformly distributed at constant porosity, which does not significantly change the velocity distribution and pollutant concentration in the street canyon
Evolution of the Miocene megalake in the western Qaidam Basin, northwestern China
No full textThick Miocene lacustrine deposits have been identified across the Qaidam Basin on the northeast Tibetan Plateau, indicative of a relatively unified megalake then. How this megalake evolved at its final stage and associated controlling factors, e.g., global climate or tectonic uplift, remain largely elusive. Here we use the KC-1 well, drilled at the depo-center of the western Qaidam Basin, to investigate the megalake evolution over the mid- and late Miocene. A set of lipid biomarker indices, namely beta-carotane/n-C-36, gammacerane index, terrigenous/aquatic ratio and long-chain saturated ketone content, altogether indicate substantial lake level fluctuations, with lower lake level at the intervals of similar to 18-17 Ma, 13.5-11.5 Ma, 10.5-8 Ma and 7-6 Ma, and higher level at the intervals of similar to 7-13.5 Ma, 11.5-10.5 Ma, 8-7 Ma and 6-5 Ma, superimposed on the long-term shrinking trend. Direct comparison with existing regional and global temperature records suggests that such lake dynamics was largely associated with global climatic conditions, i.e., shrinking under relatively cool conditions and vice versa, for both its long-term evolution and secondary fluctuations. It thus appears that global climatic conditions had controlled the megalake status during the mid- and late Miocene, whereas tectonic activities then might have also contributed to its long-term gradual demise
Vegetation dynamics and climate variability over the past 2000 years inferred from Son Kul marsh in the western Tianshan Mountains
No full textA pollen study was conducted on an alpine marsh sediment in the Son Kul Basin and was allowed to reconstruct changes in vegetation dynamics and climatic information in the western Tianshan Mountains during the past 2000 years. Pollen diagram reveals that regional vegetation is dominated by alpine meadow in the past 2000 years, being similar with modern vegetation components in the basin. The Artemisia/Chenopodiaceae-indicated moisture exhibits a warm-dry Roman Warm Period (RWP, similar to 0-similar to 500 AD), a cold-dry Dark Ages Cold Period (DACP, similar to 500-similar to 800 AD), a warm-wet Medieval Warm Period (MWP, similar to 800-similar to 1350 AD), a cold-dry Little Ice Age (LIA, similar to 1350-similar to 1850 AD) and a warm-dry Current Warm Period (CWP, since similar to 1850 AD). Our pollen-based moisture reconstructions are supported by other nearby moisture records. Combined with other pollen data in the western Tianshan Mountains, we found that the vegetation was relatively stable before similar to 1650-similar to 1750 AD and the anthropogenic activities obviously intensified afterwards (especially at the middle-elevation sites). Further work involving more and higher-resolution palaeovegetation records would contribute to fully understand the information on the complex links between environmental, climatic and anthropogenic changes in the western Tianshan Mountains
Diurnal Variations of Size-Resolved Bioaerosols During Autumn and Winter Over a Semi-Arid Megacity in Northwest China
No full textBioaerosols have a major negative effect on air quality and on public health by causing the spread of diseases. This study evaluated the bioaerosol composition and variation in a semi-arid megacity of northwest China from October 2019 to January 2020 using an Andersen six-stage impactor sampler. The size distribution, diurnal variations of the concentrations of airborne bacteria, airborne fungi, and total airborne microbes (TAM) were investigated in autumn and winter. The mean concentrations of airborne bacteria, fungi, and TAM were 523.5 +/- 301.1 colony-forming units (CFU)/m(3), 1318.9 +/- 447.8 CFU/m(3), and (7.25 +/- 1.90) x 10(6) cells/m(3), respectively, in autumn and 581 +/- 305.4 CFU/m(3), 1234.4 +/- 519.9 CFU/m(3), and (5.96 +/- 1.65) x 10(6) cells/m(3), respectively, in winter. The mean bioaerosol concentrations were slightly higher on nonhaze days than on haze days, but the difference was not statistically significant. Higher ambient particulate matter levels and atmospheric oxidation capacity inhibited bacteria survival. The diurnal maximum bioaerosol concentration was observed in the morning in autumn, whereas in winter, bioaerosols did not exhibit such a distribution, the impact of human activities on bioaerosols was still uncertain. The size of airborne bacteria exhibited a bimodal distribution, whereas a unimodal pattern was observed for fungi and TAM. Most bacteria, fungi, and TAM were distributed in the respirable ranges from trachea and primary bronchi to alveoli, indicating that bioaerosols have a high risk of being inhaled and causing respiratory diseases in Xi'an
Changes in soil water holding capacity and water availability following vegetation restoration on the Chinese Loess Plateau
No full textChanges in land use type can lead to variations in soil water characteristics. The objective of this study was to identify the responses of soil water holding capacity (SWHC) and soil water availability (SWA) to land use type (grassland, shrubland and forestland). The soil water characteristic curve describes the relationship between gravimetric water content and soil suction. We measured the soil water characteristic parameters representing SWHC and SWA, which we derived from soil water characteristic curves, in the 0-50 cm soil layer at sites representing three land use types in the Ziwuling forest region, located in the central part of the Loess Plateau, China. Our results showed that the SWHC was higher at the woodland site than the grassland and shrubland, and there was no significant difference between the latter two sites, the trend of SWA was similar to the SWHC. From grassland to woodland, the soil physical properties in the 0-50 cm soil layer partially improved, BD was significantly higher at the grassland site than at the shrubland and woodland sites, the clay and silt contents decreased significantly from grassland to shrubland to woodland and sand content showed the opposite pattern, the soil porosity was higher in the shrubland and woodland than that in the grassland, the soil physical properties across the 0-50 cm soil layer improved. Soil texture, porosity and bulk density were the key factors affecting SWHC and SWA. The results of this study provide insight into the effects of vegetation restoration on local hydrological resources and can inform soil water management and land use planning on the Chinese Loess Plateau
Seasonality of the altitude effect on leaf wax n-alkane distributions, hydrogen and carbon isotopes along an arid transect in the Qinling Mountains
No full textReconstructing paleoelevation allows the temporal evolution of biogeochemical processes and hydroclimate regimes to be understood and quantified. A dual-isotope biomarker of clumped hydrogen and carbon isotopes of leaf wax n-alkanes was recently proposed in humid tropical forests, and it was proven to be superior to a single-isotope proxy that was previously reported. However, it remains unknown whether the dual-isotope biomarker is suitable in arid conditions. The present study investigated leaf wax n-alkane distribution, hydrogen (delta H-2(wax)) and carbon (delta C-13(wax)) isotopes in terrestrial plants along an arid mountainous transect. We found that the effects of seasonality on n-alkane distribution, delta H-2(wax) and delta C-13(wax) were minimal for all species (p > 0.05), and that species-specific delta H-2(wax) values remained almost unchanged for most species, in contrast to delta C-13(wax) values. Significant correlations between altitude and delta H-2(wax) values (R-2 = 0.54, 0.58, and 0.75 for spring, summer, and autumn, respectively), instead of delta C-13(wax) values (R-2 = 0.08, 0.43, and 0.12 with p = 0.24, 0.01, and 0.19 for spring, summer, and autumn, respectively), were observed, suggesting that delta H-2(wax) values, but not delta C-13(wax) values, can be reliably used as a proxy for reconstructing paleoelevation in arid conditions. Therefore, it will be necessary to identify other proxies to supplement delta H-2(wax) values under a dual-isotope approach in future research. (C) 2021 Elsevier B.V. All rights reserved
Air Pollution Zone Migrates South Driven by East Asian Winter Monsoon and Climate Change
No full textA variety of climatological indices have been established to illustrate the impact of climate change on air pollution in China, but major facts for causing variations of air pollution attributed to climate change are still unclear. Here, using in-situ PM2.5 (particles with the aerodynamic diameter less than 2.5 mu m) measurement, atmospheric reanalysis data and a chemical transport model, we show that meridional distribution of PM2.5 loadings is strongly modulated by the intensity of East Asian winter monsoon (EAWM). The EAWM drives the heavily polluted zone in eastern China to migrate southward, i.e., under stronger EAWM, more southward migration of air pollution occurs. We expect that the migration will likely re-distribute carbon sources- and sinks-related ecosystem, posing a new challenge for the Chinese government, who needs to implement region-different emission reduction plans in the future, to mitigate air pollution and to go carbon neutral
Paleoclimate Significance of Reconstructed Rainfall Isotope Changes in Asian Monsoon Region
No full textSpeleothem oxygen isotope (delta(18)Oc) records have been regarded as a critical reference to study past Asian monsoon variability. However, existing delta(18)Oc records in the Indian monsoon region are fragmented in time coverage and/or sampling resolution since the last deglaciation. Also, the climatic interpretation of delta(18)Oc is still obscure. Here, we report a continuous and centennial-resolved leaf wax hydrogen isotope (delta D-wax) record over the past similar to 28 ka from Lugu Lake in Indian-monsoon influenced southwestern China. Our new record shows striking consistency with the well-established delta(18)Oc record in East Asian monsoon-influenced southeastern China, revealing a spatially coherent change and thus a similar physical process in rainfall isotopes in the broader Asian monsoon region. Based on the combination with the TraCE21ka simulation, we propose reconstructed long-term and millennial-scale isotope changes could be influenced by the intensity of local convection along the monsoon trough, which extends from the Indian subcontinent across to the Philippines in summer
Paleoclimate Significance of Reconstructed Rainfall Isotope Changes in Asian Monsoon Region
No full textSpeleothem oxygen isotope (delta(18)Oc) records have been regarded as a critical reference to study past Asian monsoon variability. However, existing delta(18)Oc records in the Indian monsoon region are fragmented in time coverage and/or sampling resolution since the last deglaciation. Also, the climatic interpretation of delta(18)Oc is still obscure. Here, we report a continuous and centennial-resolved leaf wax hydrogen isotope (delta D-wax) record over the past similar to 28 ka from Lugu Lake in Indian-monsoon influenced southwestern China. Our new record shows striking consistency with the well-established delta(18)Oc record in East Asian monsoon-influenced southeastern China, revealing a spatially coherent change and thus a similar physical process in rainfall isotopes in the broader Asian monsoon region. Based on the combination with the TraCE21ka simulation, we propose reconstructed long-term and millennial-scale isotope changes could be influenced by the intensity of local convection along the monsoon trough, which extends from the Indian subcontinent across to the Philippines in summer