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Träfflista för sökning "WFRF:(Zhang Qiang) ;pers:(Xu Chong Yu)"

Sökning: WFRF:(Zhang Qiang) > Xu Chong Yu

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1.
  • Chen, Yongqin David, et al. (författare)
  • Multiscale streamflow variations of the Pearl River basin and possible implications for the water resource management within the Pearl River Delta, China
  • 2010
  • Ingår i: Quaternary International. - : Elsevier BV. - 1040-6182 .- 1873-4553. ; 226:1-2, s. 44-53
  • Tidskriftsartikel (refereegranskat)abstract
    • Long monthly streamflow series of three control hydrological stations of the Pearl River basin were analyzed by using the scanning t-test and the scanning F-test. Possible implications of the changing properties of streamflow variations for the water resource management of the Pearl River Delta are also discussed. The results indicated that: 1) more complicated changes were observed in terms of the second center moment when compared to the first original moment More significant abrupt changes of the second center moment imply more sensitive response of streamflow stability to climate changes and human activities; 2) abrupt behaviors of the first (second) center moment of the streamflow variations tend to be more sensitive to climate changes and/or human activities in the larger river basin when compared to those in the smaller river basin. These phenomena are attributed to buffering functions of more storage space of longer river channel, and more complicated and longer runoff yield and concentration processes in the river basin of larger drainage area; 3) annual minimum streamflow of the Pearl River basin tends to be increasing. This will be helpful for better human mitigation of the salinity intrusion in dry seasons across the Pearl River Delta. Annual maximum streamflow, when compared to annual minimum streamflow, shows larger-magnitude variability reflected by larger standard deviation, implying unfavorable conditions for flood mitigation in the Pearl River Delta. The results of this paper are of scientific and practical merits for water resource management and sound human mitigation to water hazards across the Pearl River Delta, and also are a good case study for similar researches in other river deltas in the world under the changing environment. (C) 2009 Elsevier Ltd and INQUA. All rights reserved.
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2.
  • Xu, Chong-Yu, et al. (författare)
  • Statistical properties of the temperature, relative humidity, and net solar radiation in the Blue Nile-eastern Sudan region
  • 2010
  • Ingår i: Journal of Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 101:3-4, s. 397-409
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents the results of the first stage of an ongoing project of evaluating the spatial and temporal variability of soil water as fundamental factors for vegetation regeneration in the arid ecosystems in the Blue Nile-eastern Sudan. The specific aim of the present study is to understand the temporal and spatial variations of the major climate variables in the region and discuss its relevance to regional climate variability and changes. In this case, we systematically analyze the major climate variables (maximum and minimum air temperature, relative humidity, and net solar radiation). To evaluate the different characteristics of the climate variables, Mann-Kendall method, two-phase regression scheme, and wavelet transform technique are used; each method has its own strength and weakness, and the results of the three methods complement each other. The results show that the annual and seasonal maximum temperatures are increasing significantly. The annual minimum temperature and minimum temperature in dry seasons are decreasing. The minimum temperature in rainy season is increasing with a smaller rate as compared with the increase of maximum temperature in the season. The difference between maximum and minimum temperature is increasing in all the seasons. Net solar radiation in the region shows a significant increasing trend in all seasons, which corresponds well with the changes of maximum temperature. Besides, significant decreasing trends can be identified for relative humidity in all the seasons.
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3.
  • Zhang, Qiang, et al. (författare)
  • Changes of atmospheric water vapor budget in the Pearl River basin and possible implications for hydrological cycle
  • 2010
  • Ingår i: Journal of Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 102:1-2, s. 185-195
  • Tidskriftsartikel (refereegranskat)abstract
    • In this study, we thoroughly analyzed abrupt behaviors, trends, and periodicity properties of water vapor flux and moisture budget entering and exiting the four edges of the Pearl River basin based on the NCAR/NCEP reanalysis dataset by using the continuous wavelet transform and the simple two-phase linear regression technique. Possible implications for hydrological cycle and water resource management of these changes are also discussed. The results indicate that: (1) the water vapor propagating through the four edges of the Pearl River basin is decreasing, and it is particularly true for the changes of the water vapor flux exiting from the north edge of the study river basin. The transition point from increase to decrease occurs in the early 1960s; (2) The wavelet transform spectra indicate that the monthly water vapor flux through the north edge decreases and this decrease is mainly reflected by intermittent distribution of the wavelet power spectra after early 1980s. The periodicity properties of the water vapor flux through the north edge imply that the northward propagation of water vapor flux decreases after the 1980s; (3) close relations between water vapor flux, precipitation and streamflow implies that the altered hydrological cycle in the Pearl River basin is mainly manifested by seasonal shifts of water vapor flux after early 1960s. One of the direct consequences of these changes of water vapor flux is the seasonal transition of wet and dry conditions across the Pearl River basin. Regional responses of hydrological cycle to climate variation/change could be different from one river basin to another. Hydrological responses of the Pearl River basin to the global warming are mainly demonstrated by seasonal shifts of precipitation changes: winter comes to be wetter and summer tends to be dryer. The finding of the seasonal transition of precipitation in the Pearl River basin is of great scientific and practical merits in basin scale water resource management in the Pearl River basin under the changing climate and global warming in particular.
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4.
  • Zhang, Qiang, et al. (författare)
  • Changes of temperature extremes for 1960-2004 in Far-West China
  • 2009
  • Ingår i: Stochastic environmental research and risk assessment (Print). - : Springer Science and Business Media LLC. - 1436-3240 .- 1436-3259. ; 23:6, s. 721-735
  • Tidskriftsartikel (refereegranskat)abstract
    • The spatial and temporal patterns of the temperature extremes defined by 5th and 95th percentiles based on daily maximum/minimum temperature dataset were analyzed using Mann-Kendall test and linear regression method. The research results indicate that: (1) the seasonal minimum temperature is in stronger increasing trend than the seasonal maximum temperature; (2) in comparison with the changes of the maximum temperature, more stations display significantly increasing trends of minimum temperature in frequency and intensity; (3) comparatively, more stations have significantly decreasing trends in the intra-seasonal extreme temperature anomaly in summer and winter than in spring and autumn. The areal mean minimum temperature is in stronger increasing trend than areal mean maximum temperature; (4) the warming process in the Far-West (FW) China is characterized mainly by significantly increasing minimum temperature. The research will be helpful for local human mitigation to alterations in water resource and ecological environment in FW China due to changes of temperature extremes, as the ecologically fragile region of China.
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5.
  • Zhang, Qiang, et al. (författare)
  • Observed changes of drought/wetness episodes in the Pearl River basin, China, using the standardized precipitation index and aridity index
  • 2009
  • Ingår i: Journal of Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 98:1-2, s. 89-99
  • Tidskriftsartikel (refereegranskat)abstract
    • Monthly precipitation data of 42 rain stations over the Pearl River basin for 1960-2005 were analyzed to classify anomalously wet and dry conditions by using the standardized precipitation index (SPI) and aridity index (I) for the rainy season (April-September) and winter (December February). Trends of the number of wet and dry months decided by SPI were detected with Mann-Kendall technique. Furthermore, we also investigated possible causes behind wet and dry variations by analyzing NCAR/NCEP reanalysis dataset. The results indicate that: (1) the Pearl River basin tends to be dryer in the rainy season and comes to be wetter in winter. However, different wetting and drying properties can be identified across the basin: west parts of the basin tend to be dryer; and southeast parts tend to be wetter; (2) the Pearl River basin is dominated by dry tendency in the rainy season and is further substantiated by aridity index (I) variations; and (3) water vapor flux, moisture content changes in the rainy season and winter indicate different influences of moisture changes on wet and dry conditions across the Pearl River basin. Increasing moisture content gives rise to an increasing number of wet months in winter. However, no fixed relationships can be observed between moisture content changes and number of wet months in the rainy season, indicating that more than one factor can influence the dry or wet conditions of the study region. The results of this paper will be helpful for basin-scale water resource management under the changing climate.
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6.
  • Zhang, Qiang, et al. (författare)
  • Precipitation extremes in a karst region : a case study in the Guizhou province, southwest China
  • 2010
  • Ingår i: Journal of Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 101:1-2, s. 53-65
  • Tidskriftsartikel (refereegranskat)abstract
    • We analyzed the changing properties of precipitation extremes in the Guizhou province, a region of typical karst geomorphology in China. Precipitation extremes were defined by the largest 1- and 5-day precipitation total. Trends of precipitation extremes were detected by using Mann-Kendall trend test technique. Besides, we also investigated moisture flux variations based on the National Centers for Environmental Prediction and the National Center for Atmospheric Research reanalysis dataset with the aim to further explore the possible causes behind the changes in precipitation extremes. The results of this study indicated that: (1) Although the changes in precipitation extremes at most of the stations were not significant, enhanced precipitation extremes were still detected after the early 1990s mainly in the middle and west parts of the Guizhou province; (2) In winter, east and south parts of the Guizhou province were characterized by increasing precipitation extremes; In summer, enhanced precipitation extremes were observed mainly in the middle and east parts of the Guizhou province; (3) A significant increase of moisture flux was observed after the 1990s when compared to that before the 1990s. Cumulative departure analysis results of moisture flux and precipitation extremes confirmed the influences of moisture flux on the variations of precipitation extremes in the study region. This study clarified the changes of weather extremes and their linkages with large-scale atmospheric circulation in the karst region of China, which will definitely enhance human mitigation to natural hazards in the fragile ecological environment under the influences of changing climate.
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7.
  • Zhang, Qiang, et al. (författare)
  • Spatial and temporal variability of precipitation maxima during 1960-2005 in the Yangtze River basin and possible association with large-scale circulation
  • 2008
  • Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 353:3-4, s. 215-227
  • Tidskriftsartikel (refereegranskat)abstract
    • This study investigated spatial and temporal patterns of trends of the precipitation maxima (defined as the annual./seasonal. maximum precipitation) in the Yangtze River basin for 1960-2005 using Mann-Kendall trend test, and explored association of changing patterns of the precipitation maxima with large-scale circulation using NCEP/NCAR reanalysis data. The research results indicate changes of precipitation maxima from relative stable patterns to the significant increasing/decreasing trend in the middle 1970s. With respect to annual variability, the rainy days are decreasing and precipitation intensity is increasing, and significant increasing trend of precipitation intensity was detected in the middle and lower Yangtze River basin. Number of rain days with daily precipitation exceeding 95th and 99th percentiles and related precipitation intensities are in increasing tendency in summer. Large-scale atmospheric circulation analysis indicates decreasing strength of East Asian summer monsoon during 1975-2005 as compared to that during 1961-1974 and increasing geopotential height in the north China, South China Sea and west Pacific regions, all of which combine to negatively impact the northward propagation of the vapor flux. This circulation pattern will be beneficial for the longer stay of the Meiyu front in the Yangtze River basin, leading to more precipitation in the middle and lower Yangtze River basin in summer months. The significant increasing summer precipitation intensity and changing frequency in the rain/no-rain days in the middle and lower Yangtze River basin have potential to result in higher occurrence probability of flood and drought hazards in the region.
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8.
  • Chen, David, et al. (författare)
  • CHANGE-POINT ALTERATIONS OF EXTREME WATER LEVELS AND UNDERLYING CAUSES IN THE PEARL RIVER DELTA, CHINA
  • 2009
  • Ingår i: Rivers Research and Applications. - : Wiley. - 1535-1459 .- 1535-1467. ; 25, s. 1153-1168
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, the Bayesian model and Lepage test were used to detect change point and to analyse associated statistical properties of high/low water levels in summer (June, July and August (JJA)) and winter (December, January and February (DJF)) months across the PRD (Pearl River Delta). The results indicate that: (1) two time intervals, that is 1979-1981 and 1988-1995, witness abrupt changes of SmH/SmL (summer mean high water level/summer mean low water level). The lower PRD is dominated by increased mean and coefficient of variation (Cv) of SmH. Increased mean but decreased Cv of SmL can be observed in the Mainstem Pearl River; (2) WmL (winter mean low water level) and WmH (winter mean high water level) of about 74% of the total stations have two change points occurred roughly during 1969-1971 and 1993-1995. First change points of WmH are mainly characterized by increased mean and Cv, but decreased mean and increased Cv of WmL can be observed across major parts of the PRD. The driving factors causing abrupt changes of water levels are various. Intensive human activities cannot be ignored, for example in-channel dredging and reallocation of the streamflow within the river channels due to human-induced topographical changes of river channel. Different responses of high/low water levels to externally influencing factors and interactions between influencing factors make the alterations of the water levels across the PRD more complicated. The findings of this paper will be helpful for the management of the PRD and human mitigation to natural hazards under the changing environment. Copyright (C) 2008 John Wiley & Sons, Ltd.
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9.
  • Chen, David, et al. (författare)
  • Hydrologic alteration along the Middle and Upper East River (Dongjiang) basin, South China : a visually enhanced mining on the results of RVA method
  • 2010
  • Ingår i: Stochastic environmental research and risk assessment (Print). - : Springer Science and Business Media LLC. - 1436-3240 .- 1436-3259. ; 24, s. 9-18
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents a visually enhanced evaluation of the spatio-temporal patterns of the dam-induced hydrologic alteration in the middle and upper East River, south China over 1952-2002, using the range of variability approach (RVA) and visualization package XmdvTool. The impacts of climate variability on hydrological processes have been removed for wet and dry periods, respectively, so that we focus on the impacts of human activities (i.e., dam construction). The results indicate that: (1) along the East River, dams have greatly altered the natural flow regime, range condition and spatial variability; (2) six most remarkable indicators of hydrologic alteration induced by dam-construction are rise rate (1.16), 3-day maximum (0.91), low pulse duration (0.88), January (0.80), July (0.80) and February (0.79) mean flow of the East River during 1952-2002; and (3) spatiotemporal hydrologic alterations are different among three stations along Easter River. Under the influence of dam construction in the upstream, the degree of hydrologic changes from Lingxia, Heyuan to Longchuan station increases. This study reveals that visualization techniques for high-dimensional hydrological datasets together with RVA are beneficial for detecting spatio-temporal hydrologic changes.
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10.
  • Shen, Zexi, et al. (författare)
  • Mining Can Exacerbate Global Degradation of Dryland
  • 2021
  • Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 48:21
  • Tidskriftsartikel (refereegranskat)abstract
    • Groundwater storage (GS) is the major water resource for vegetation in drylands. Thus, positive relationships between vegetative growth condition (VGC) and GS are expected in drylands. Since mining-induced dewatering tends to deplete GS surrounding mine sites, VGC should become less favorable due to a shortage of accessible water. However, quantitative analysis repealed the opposite. We found that global annual mineral production in drylands increased by 24%, while GS decreased by 22% but the VGC improved by 37% (2002–2010). And negative relationships between VGC and GS were detected in 84.7% of global dryland mine sites. We concluded that irrigation supported by mining-induced dewatering promoted the vegetation growth surrounding mine sites. However, since the GS is limited, irrigation-supported vegetation growth is unsustainable. This study elucidates the reason behind these abnormal negative relationships and highlights the potential risk of vegetation degradation induced by unsustainable groundwater depletion in global dryland mine sites.
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  • Resultat 1-10 av 24

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