Cryospheric Changes and Their Impacts on Water Resources in the Belt and Road Regions     

Shichang Kang  Wanqin Guo  Tonghua Wu  Xinyue Zhong  Rensheng Chen  Min Xu  Jinlei Chen  Ruimin Yang 《地球科学进展》2020,35(1):1-17

“Belt and Road” regions include Asia, Europe and eastern and northern Africa, with a wide spatial distribution. The cryosphere is undergoing rapid changes in the Belt and Road regions with global warming, and has an important impact on water resources, ecosystems and Arctic waterways in these regions. This article reviewed recent cryospheric changes and associated impacts on water resources in the Belt and Road regions during the last decades. The main cognitions are as follows: \mathrm{①} Most glaciers are shrinking and glacier mass balances are most negative, but there are regional differences in the changes of glaciers. \mathrm{②} Global temperature rise has resulted in permafrost degradation, including a rise in permafrost temperature and decreasing permafrost thickness as well as an increase in active layer thickness. \mathrm{③} There is a significant decrease in snow cover extent and an increase in snow depth. Snow cover duration has shortened, the onset of snow cover has delayed, and the end of snow cover has advanced. However, there are still obvious regional differences in the changes of snow cover. \mathrm{④} Arctic sea ice has declined precipitously in both extent and thickness in summer, and multi-year sea ice has decreased，indicating the precipitous retreat of sea ice. The freeze-up date of some lakes has been delayed, the break-up date has advanced, and the ice cover duration of river/lake ice has significantly shortened. \mathrm{⑤} Glacial runoff has increased significantly in China. Snowmelt and permafrost degradation have also increased the basin runoff, which indicates the important impact of cryospheric changes on runoff. This study will provide a baseline and important scientific support for addressing climate change and regional sustainable development.  相似文献   

Spatio-temporal differentiation of spring phenology in China driven by temperatures and photoperiod from 1979 to 2018     

Wu  Xiaojing  Cheng  Changxiu  Qiao  Cancan  Song  Changqing 《中国科学:地球科学(英文版)》2020,63(10):1485-1498

Large amounts of data accumulated in ecology and related environmental sciences arouses urgent need to explore useful patterns and information in it. Here we propose coclustering-based methods and a temperatures-photoperiod driven phenological model to explore spatio-temporal differentiation in long-term spring phenology in China. First, we created the first bloom date(FBD) dataset in China from 1979 to 2018 using the extended spring indices and China Meteorological Forcing Dataset. Then we analyzed the dataset using Bregman block average co-clustering algorithm with I-divergence(BBAC_I) and kmeans algorithm. Such analysis delineated the spatially-continuous phenoregions in China for the first time. Results showed three spatial patterns of FBD in China and their temporal dynamics for 40 years(1979–2018). More specifically, overall late spring onsets occur in 1979–1996, in which areas located in Jiangxi, northern Xinjiang and middle Inner Mongolia experienced constant changing spring onsets. Overall increasingly earlier spring onsets occur in 1997–2012, in which areas located in Fujian,Hunan and eastern Heilongjiang experienced the most variable spring onsets. Stable early spring onsets over China occur after 2012. Results also showed 15 temporal patterns of spring phenology over the study period and their spatial delineation in China.More specifically, most areas in China have the same FBD category for 40 years while northern Guizhou, Hunan and southern Hubei have the same category in 1979–1997 and then fluctuate between different categories. Finally, our results have certain directive significance on the design of existing observational sites in Chinese Phenological Network.  相似文献   

Composition and flux of suspended organic matter in the middle and lower reaches of the Changjiang (Yangtze River) — impact of the Three Gorges Dam and the role of tributaries and channel erosion          下载免费PDF全文

Hongyan Bao  Ying Wu  Jing Zhang  Bing Deng  Qing He 《水文研究》2014,28(3):1137-1147

To investigate the sources of particulate organic matter (POM) and the impact of Three Gorges Dam (TGD), two large lakes and erosion processes on determining the composition and flux of POM in low water discharge periods along the middle and lower Changjiang, suspended particulate samples were collected along the middle and lower reaches of the Changjiang (Yangtze River) in January 2008. Organic geochemistry of bulk sediment (particulate organic carbon, organic carbon to nitrogen molar ratio (C/N), stable carbon isotope (δ¹³C) and grain size) and biomarker of bulk sediment (lignin phenols) were measured to trace the sources of POM. The range of C/N ratios (6.4–8.9), δ¹³C (?24.3‰ – ?26.2‰) and lignin phenols concentration Λ8 (0.45 mg/100 mg OC‐2.00 mg/100 mg OC) of POM suggested that POM originated from the mixture of soil, plant tissue and autochthonous organic matter (OM) during the dry season. POM from lakes contained a higher portion of terrestrial OM than the mainstream, which was related to sand mining and hydropower erosion processes. A three end‐member model based on δ¹³C and Λ8 was performed. The results indicated that soil contributed approximately 50% of OM to the POM, which is the dominant OM source in most stations. POM composition was affected by total suspended matter (TSM) and grain size composition, and the direct OM input from two lakes and channel erosion induced OM. The lower TSM concentration in January 2008 was mainly caused by seasonal variations; the impact from the TGD in the dry season was relatively small. A box model indicated that more than 90% of the terrestrial OM transported by the Changjiang in January 2008 was from the middle and lower drainage basins. Channel erosion induced OM, and contributions from Poyang Lake were the major terrestrial OM sources in the dry season. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Measurement of stream cross section using ground penetration radar with Hilbert–Huang transform          下载免费PDF全文

Yen‐Chang Chen  Su‐Pai Kao  Jhong‐Hua Wu 《水文研究》2014,28(4):2468-2477

This study presents a new method to measure stream cross section without having contact with water. Compared with conventional measurement methods which apply instruments such as sounding weight, ground penetration radar (GPR), used in this study, is a non‐contact measurement method. This non‐contact measurement method can reduce the risk to hydrologists when they are conducting measurements, particularly in high flow period. However, the original signals obtained by using GPR are very complex, different from studies in the past where the measured data were mostly interpreted by experts with special skill or knowledge of GPR so that the results obtained were less objective. This study employs Hilbert–Huang transform (HHT) to process GPR signals which are difficult to interpret by hydrologists. HHT is a newly developed signal processing method that can not only process the nonlinear and non‐stationary complex signals, but also maintain the physical significance of the signal itself. Using GPR with HHT, this study establishes a non‐contact stream cross‐section measurement method with the ability to measure stream cross‐sectional areas precisely and quickly. Also, in comparison with the conventional method, no significant difference in results is found to exist between the two methods, but the new method can considerably reduce risk, measurement time, and manpower. It is proven that the non‐contact method combining GPR with HHT is applicable to quickly and accurately measure stream cross section. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Diatom‐based reconstruction of summer sea‐surface salinity in the South China Sea over the last 15 000 years     

Hui Jiang  Mads F. Knudsen  Marit‐Solveig Seidenkrantz  Meixun Zhao  Longbin Sha  Lihua Ran 《Boreas: An International Journal of Quaternary Research》2014,43(1):208-219

We present a new reconstruction of summer sea‐surface salinity (SSS) over the past 15 000 years based on a diatom record from piston core 17940, located on the northern slope of the South China Sea (SCS). The reconstructed diatom‐based summer SSS values for the modern period are in accord with instrumental observations of summer SSS in the area. Here, the modern summer SSS is primarily controlled by river runoff, in particular from the Pearl River. The reconstruction presented in this study shows that the summer SSS varied between 33.3 and 34.2 psu over the past 15 000 years. The long‐term summer SSS trend closely followed the trend of the orbitally controlled solar insolation at 20°N, suggesting that orbital forcing was the dominant driver of changes in summer SSS in this area. Comparisons to speleothem δ¹⁸O data and studies of surface hydrography in the region suggest that changes in solar insolation affected the summer SSS through changes in the East Asian Monsoon and sea‐level changes associated with the last deglaciation. Univariate spectral analyses indicate that centennial‐scale oscillatory variations in summer SSS were superimposed on the long‐term trend. During the deglacial period (c. 12 000–9000 cal. a BP), the dominant periodicity was centred around 230–250 years, whereas a ～350‐year oscillation dominated in the period 2200–4500 cal. a BP. The balance of evidence suggests that these centennial‐scale changes in summer SSS may have been driven by solar‐induced changes in the East Asian Monsoon, but further evidence is needed to firmly establish this relationship.  相似文献   

Thorium distribution on the lunar surface observed by Chang’E-2 gamma-ray spectrometer     

Xianmin Wang  Xubing Zhang  Ke Wu 《Astrophysics and Space Science》2016,361(7):234

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KOSMA 12CO(2–1) and (3–2) observations toward Infrared Dark Clouds     

Dalei Li  Jarken Esimbek  Jianjun Zhou  Willem Baan  Gang Wu  Xindi Tang  Weiguang Ji  Ye Yuan  Yuxin He  Toktarkhan Komesh 《Astrophysics and Space Science》2016,361(7):220

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The Broken Lane of a Type II Radio Burst Caused by Collision of a Coronal Shock with a Flare Current Sheet     

Guannan Gao  Min Wang  Ning Wu  Jun Lin  E. Ebenezer  Baolin Tan 《Solar physics》2016,291(11):3369-3384

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Turnover Frequency in Solar Microwave Bursts with an Extremely Flat Optically Thin Spectrum     

Q. W. Song  H. Nakajima  G. L. Huang  B. L. Tan  Y. Huang  Z. Wu 《Solar physics》2016,291(12):3619-3635

Four microwave bursts have been selected from the Nobeyama Radio Polarimeter (NoRP) observations with an extremely flat spectrum in the optically thin part and a very hard spectral index between 0 and ?1 in the maximum phase of all bursts. It is found that the time evolution of the turnover frequency is inversely proportional to the time profiles of the radio flux in all bursts. Based on the nonthermal gyrosynchrotron theory of Ramaty (Astrophys. J. 158, 753, 1969), the local magnetic field strength and the electron spectral index are calculated uniquely from the observed radio spectral index and the turnover frequency. We found that the electron energy spectrum is very hard (spectral index 1?–?2), and the time variation of the magnetic field strength is also inversely proportional to the radio flux as a function of time in all bursts. Hence, the time evolution of the turnover frequency can be explained directly by its dependence on the local magnetic field strength. The high turnover frequency (several tens of GHz) is mainly caused by a strong magnetic field of up to several hundred gauss, and probably by the Razin effect under a high plasma density over \(10^{10}~\mbox{cm}^{-3}\) in the maximum phase of these bursts. Therefore, the extremely flat microwave spectrum can be well understood by the observed high turnover frequency and the calculated hard electron spectral index.  相似文献   

北羌塘地块上石炭统瓦垄山组的珊瑚化石     

张少文  李涌溪  武桂春  纪占胜 《地质论评》2021,67(Z1):67z1249-67z1250

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