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The locust plagues of the Ming and Qing dynasties in the Xiang-E-Gan region, China
No full textBased on the historical documents of Ming and Qing dynasties, with the help of mathematical statistics and the ArcGIS spatial analysis method, this study reconstructed grades and counties affected by locust plagues to examine their spatiotemporal characteristics, environmental significance and social impact. The results show that: (1) There were 242 locust plague years in the Xiang-E-Gan region during the Ming and Qing dynasties, with an average of one outbreak every 2.25 years. The Qing dynasty suffered more than the Ming dynasty, and Hubei Province was affected more seriously than Jiangxi Province and Hunan Province. Locust plagues mostly occurred from March to August, and autumn locust plagues occurred more frequently than summer locust plagues. (2) The sixteenth, seventeenth and nineteenth centuries were periods of successive outbreaks, with 4.13 locust plague years and 10.75 affected counties per decade. The spatial heterogeneity and aggregation of locust outbreaks were significant, and the plain area was affected more seriously and continuously. (3) Low temperature promoted the outbreak of locust plagues, especially during the period of high occurrence, and the outbreaks cannot indicate the previous year's temperature. Compared with floods, the relationship between droughts and locust plague was closer, and large-scale climate change may also affect locust outbreaks. (4) Long-term natural disasters multiplied the food price and food prices lagged behind disasters. Epidemics were often accompanied by locust plagues, forming a typical chain of agricultural disasters that did great harm to the society
Changes in the Tree-Ring Width-Derived Cumulative Normalized Difference Vegetation Index over Northeast China during 1825 to 2013 CE
No full textVegetation coverage is very important in terrestrial ecosystems and climate systems. However, the observational record of the normalized difference vegetation index (NDVI), which started in the 1980s when satellites became widely used, is too short to investigate the history of variation in vegetation coverage beyond the modern observation period. Here, we present a 189 y vegetation coverage series based on a total of 349 Mongolian pine (Pinus sylvestris var. mongolica Litv) cores from seven locations from the central-western Da Hinggan Mountains (CW-DHM), northeastern China. We found a significant relationship between tree-ring width and the regional cumulative normalized difference vegetation index (CNDVI). The correlation between the ring-width chronology and the regional June-July CNDVI (CNDVIJJ) was significant, with r = 0.68 (n = 32, p < 0.001) and an explained variance of 45.8% (44.0% after the adjustment for the loss of the degree of freedom). On this basis, we designed a transfer function to reconstruct the CNDVIJJ for the CW-DHM region from 1825 to 2013 CE (Common Era). During the last 189 years, there were 28 years with high CNDVIJJ values, and another 28 years with low values. We also observed CNDVIJJ fluctuations at the inter-annual and decadal time scales, including eight low value periods and nine high value periods. Based on our analysis, the variation in CNDVI is associated with climatic factors, such as temperature, precipitation and the Palmer Drought Severity Index (PDSI), which combines both temperature and precipitation. From 1950 to 2002 CE, the CNDVI showed a noticeable decreasing trend in the CW-DHM region, whereas after 2003 CE, the CNDVI exhibited an apparent increase, which has also been observed in southern Central Siberia, eastern Mongolia and northeastern and eastern China, indicating that the CNDVI change in the CW-DHM is related to climate change in the local region and in some parts of Asia
Global, continental, and national variation in PM2.5, O-3, and NO2 concentrations during the early 2020 COVID-19 lockdown
No full textLockdowns implemented in response to COVID-19 have caused an unprecedented reduction in global economic and transport activity. In this study, variation in the concentration of health-threatening air pollutants (PM2.5, NO2, and O-3) pre- and post-lockdown was investigated at global, continental, and national scales. We analyzed ground-based data from >10,000 monitoring stations in 380 cities across the globe. Global-scale results during lockdown (March to May 2020) showed that concentrations of PM2.5 and NO2 decreased by 16.1% and 45.8%, respectively, compared to the baseline period (2015-2019). However, O-3 concentration increased by 5.4%. At the continental scale, concentrations of PM2.5 and NO2 substantially dropped in 2020 across all continents during lockdown compared to the baseline, with a maximum reduction of 20.4% for PM2.5 in East Asia and 42.5% for NO2 in Europe. The maximum reduction in O-3 was observed in North America (7.8%), followed by Asia (0.7%), while small increases were found in other continents. At the national scale, PM2.5 and NO2 concentrations decreased significantly during lockdown, but O-3 concentration showed varying patterns among countries. We found maximum reductions of 50.8% for PM2.5 in India and 103.5% for NO2 in Spain. The maximum reduction in O-3 (22.5%) was found in India. Improvements in air quality were temporary as pollution levels increased in cities since lockdowns were lifted. We posit that these unprecedented changes in air pollutants were mainly attributable to reductions in traffic and industrial activities. Column reductions could also be explained by meteorological variability and a decline in emissions caused by environmental policy regulations. Our results have implications for the continued implementation of strict air quality policies and emission control strategies to improve environmental and human health
Global-scale altitude effect on leaf wax n-alkane delta D values in terrestrial higher plants
No full textNumerous field studies have shown that leaf wax n-alkane delta D values (delta Dn-alkane) can be used as a proxy for paleoelevation reconstruction. However, the lack of systematic global analysis of delta Dn-alkane values with respect to altitude limits the reliability of delta Dn-alkane values for paleoaltimetry at the global scale. In this study, we analyzed the variation of delta Dn-alkane values with altitude in terrestrial higher plants based upon our compiled global delta Dn-alkane database. The general decrease in delta Dn-alkane values with altitude corresponds to the variation in precipitation delta D (delta D-prec) with altitude, suggesting that the delta Dn-alkane values effectively reflect delta D-prec values. When eliminating the effect of latitude at the global scale, the global delta Dn-alkane-altitude lapse rate for all species was -1.01 +/- 0.10 parts per thousand (100 m)(-1), while these lapse rates were -1.03 +/- 0.13 parts per thousand and -0.47 +/- 0.13 parts per thousand (100 m)(-1) for dicots and monocots, respectively. Our study reveals that it is reliable to use delta Dn-alkane values to gain information about paleoelevation at the global scale, and the global delta Dn-alkane-altitude lapse rates provide an alternative to reconstruct paleoelevation at some delta Dn-alkane-uninvestigated areas
Two-stage evolution of glacial-period Asian monsoon circulation by shifts of westerly jet streams and changes of North American ice sheets
No full textCompilation of North American loess, dune, lacustrine, and glacial moraine morphological records at places along the retreating Laurentide Ice Sheet shows intra D-O/Heinrich-scale climate oscillations between 28,000 and 10,000 calibrated years before present (calBP). Grayscale variations of the loess-paleosol record that represents the composite stratigraphy reflect the poleward-equatorward displacement of westerly jet stream, associated with advance-retreat of the Laurentide Ice Sheet, both of which superpose on a 2-stage trend of drastic changes. Compilation of paleo-Asian monsoon records from NE, East Central, and SW China also shows a 2-stage evolution of Asian monsoon rainbelt distribution with patterns on intra D-O/Heinrich scales between 28,000 and 10,000 calBP. In stage 1, Asian monsoon rainfall intensity decreases over NE/SW but increases over EC, then drastically fluctuates over NE/SW and keeps constant over EC China. In stage 2, Asian monsoon rainbelts distribute a modern-synoptic-style tripole and reversed tripole mode during boreal interstadials and stadials. Additional compilation of more paleo-Asian monsoon rainfall records and state-of-the-science model precipitation records confirms these patterns over large geographic region and Asian continent during this period. The comparison of global climate forcing factors excludes Atlantic Meridional Overturning Circulation but suggests poleward-equatorward displacements of North American westerly jet streams coupled with ice sheet margin fluctuations at middle to upper midlatitudes, which altered the structures of Eurasian jet streams, to modulate the 2-stage intra D-O/Heinrich-scale changes on Asian monsoon evolution. The drastic retreating of the Laurentide Ice sheet during the second stage made the modern-synoptic-style monsoon rainbelt distribution with seesaw patterns on intra D-O/Heinrich warm and cold phases prominent at 16,000 calBP
How dusty was the last glacial maximum over Europe?
No full textOur study focuses on European loess sequences, particularly the eolian intervals in between the observed pedogenic units. The classical concept of soil formation from parent material is reformulated to estimate of the duration and the associated sedimentation rate (SR) and mass accumulation rate (MAR) of these paleodust intervals. We show that the Greenland Stadial (GS) duration in European loess deposits includes the thickness of the overlying pedogenic unit, which in fact developed downward into the upper part of the eolian unit. The lower stratigraphical limit of the eolian unit overlying the pedogenic unit corresponds to the restart of the dust sedimentation of the younger GS. We illustrate this interpretation first by computing both SRs and MARs first for the Nussloch key sequence, the most complete European series. The correlation between Nussloch and other European loess sequences, located along a 1800 km longitudinal transect, allows computation of SR and MAR for several identified GS events. Comparing GS from marine and ice core records, our study shows that the two last Bond cycles are preserved in every European eolian record.
Bulk SR and MAR are estimated and compared for these two Bond cycles, showing the highest SRs and MARs in western Europe. These indices also indicate that the last stadials, embedding an Henrich event, were not the dustiest in every Bond cycle. Our estimated MAR also differ from previously published computations, which did not take into account the various pedogenic units present in the studied loess sequences. The bulk SR and MAR estimates computed for the two last Bond Cycles from Chinese sequences from the Loess Plateau indicate lower atmospheric dust than in Europe during the Last Glacial Maximum. SR and MAR estimates computed from the fine-grained material for European records fit with Earth System model reconstructions. (C) 2020 Elsevier Ltd. All rights reserved
Toxicological effects of personal exposure to fine particles in adult residents of Hong Kong
No full textToxicological studies have demonstrated the associations between fine particle (PM2.5) components and various cytotoxic endpoints. However, few studies have investigated the toxicological e?ects of source-specific PM2.5 at the individual level. To investigate the potential impact of source-specific PM2.5 on cytotoxic effects, we performed repeated personal PM2.5 monitoring of 48 adult participants in Hong Kong during the winter and summer of 2014-2015. Quartz filters were analyzed for carbonaceous aerosols and water-soluble ions in PM2.5. Teflon filters were collected to determine personal PM2.5 mass and metal concentrations. The toxicological effects of personal PM2.5 exposure-including cytotoxicity, inflammatory response, and reactive oxygen species (ROS) production-were measured using A549 cells in vitro. Personal PM(2.)5 samples collected in winter were more effective than those collected in summer at inducing cytotoxicity and the expression of proinflammation cytokine IL-6. By contrast, summer personal PM2.5 samples induced high ROS production. We performed a series of statistical analyses, Spearman correlation and a source apportionment approach with a multiple linear regression (MLR) model, to explore the sources contributing most significantly to personal PM2.5 bioreactivity. Secondary inorganic species and transition metals were discovered to be weak-to-moderately associated with cytotoxicity (r(s): 0.26-0.55; p < 0.01) and inflammatory response (r(s): 0.26-0.44; p < 0.05), respectively. Carbonaceous aerosols (i.e., organic and elemental carbon; r(s): 0.23-0.27; p < 0.05) and crustal material (Mg and Ca) was positively associated with ROS generation. The PMF-MLR models revealed that tailpipe exhaust and secondary sulfate contributed to ROS generation, whereas secondary nitrate was the major contributor to PM2.5 cytotoxicity and inflammation. These results improve and variate the arguments for practical policies designed to mitigate the risks posed by air pollution sources and to protect public health. (C) 2021 Elsevier Ltd. All rights reserved
Asymmetric Effect of El Nino-Southern Oscillation on the Spring Precipitation over South China
No full textSouth China is one of the most densely populated and agriculture-based regions in China. Local spring precipitation is crucial to the people's livelihood and social economic development. Using the observed and reanalysis datasets for the period 1958-2019, this study revealed an asymmetric effect of El Nino-Southern Oscillation (ENSO) on the following spring precipitation over South China. During the years with positive ENSO phases, a strong positive correlation between spring precipitation and the preceding winter ENSO sea surface temperature (SST) anomalies existed over Guangdong province. For the years with negative ENSO phases, such a strong positive correlation shifts westwards to Guangxi province. To be specific, the El Nino events usually result in a precipitation surplus in the decaying spring over Guangdong province, while the La Nina events usually lead to a precipitation deficit in the decaying spring over Guangxi province. This is attributed to the nonlinear effects of ENSO on the atmospheric circulation. Compared with El Nino, the abnormal center of La Nina evidently extends westwards, inducing a westward movement of the anomalous low-level atmospheric circulation, which eventually results in a westward-shifted effect on the following spring precipitation over South China. Our findings emphasize the nonlinear responses of spring precipitation over South China to ENSO. This has important implications for the seasonal climate predictions over South China
Stable isotope analysis of soil and plant water in a pair of natural grassland and understory of planted forestland on the Chinese Loess Plateau
No full textA series of revegetation programs have been carried out since 1950s, and a large area of cropland has been converted to forestland and grassland through tree plantation and natural vegetation restoration. However, it is still inadequately addressed how plant revegetation changes the characteristics of soil-plant waters. In this study, we compared delta O-18 and delta H-2 values of different waters from precipitation, soil water, root water, and leaf water between different herbaceous plants (understory of the planted forestland and natural recovered grassland) in two neighboring catchments. There was a temporal consistence in delta O-18 and delta H-2 among different waters, showing that root water and leaf water could record well the signals of soil water and precipitation, followed by temperature change over month. A series of water line equations between delta O-18 and delta H-2 indicate that herbaceous plants have higher soil evaporation for grassland than understory of the forestland, instead of leaf transpiration. Moreover, our study found significant differences in delta O-18 and delta H-2 between root water and soil water, probably associated with isotopic fractionation during root water uptake, leaf surface water pools and ecohydrological separation. This study will be helpful to better understand the effect of plant revegetation programmes (planted forestland catchment versus natural grassland catchment) on ecohydrological processes on the Chinese Loess Plateau
Drivers for Asynchronous Patterns of Dust Accumulation in Central and Eastern Asia and in Greenland During the Last Glacial Maximum
No full textWe collected 143 loess optically stimulated luminescence (OSL) ages between 10 ka and 30 ka from Central Asia (CA), and analyzed their probability density functions (PDFs). The PDFs show dust accumulation was greater during the late Last Glacial Maximum (LGM) (23-19 ka) than that during the early LGM (26.5-23 ka). The temporal variability of dust accumulation of CA loess is generally similar to that of Chinese Loess Plateau (CLP) loess, following precession. In contrast, dust accumulation in Greenland was stronger during the early LGM than that during the late LGM, following obliquity. Supported by numerical modeling experiments and our newly dating OSL ages, we conclude dust accumulation in CA and CLP during the LGM was controlled by Siberian High forced by precession, while dust accumulation in Greenland was closely related to both intensity of summer westerlies forced by obliquity, and to intensity of dust emissions at source forced by precession