| 1. |
- Xu, Chong-Yu, et al.
(författare)
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Statistical properties of the temperature, relative humidity, and net solar radiation in the Blue Nile-eastern Sudan region
- 2010
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Ingår i: Journal of Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 101:3-4, s. 397-409
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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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| 2. |
- Zhang, Qiang, et al.
(författare)
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Changes of atmospheric water vapor budget in the Pearl River basin and possible implications for hydrological cycle
- 2010
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Ingår i: Journal of Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 102:1-2, s. 185-195
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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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| 3. |
- Zhang, Qiang, et al.
(författare)
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Changes of temperature extremes for 1960-2004 in Far-West China
- 2009
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Ingår i: Stochastic environmental research and risk assessment (Print). - : Springer Science and Business Media LLC. - 1436-3240 .- 1436-3259. ; 23:6, s. 721-735
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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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| 4. |
- Zhang, Qiang, et al.
(författare)
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Observed changes of drought/wetness episodes in the Pearl River basin, China, using the standardized precipitation index and aridity index
- 2009
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Ingår i: Journal of Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 98:1-2, s. 89-99
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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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| 5. |
- Zhang, Qiang, et al.
(författare)
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Precipitation extremes in a karst region : a case study in the Guizhou province, southwest China
- 2010
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Ingår i: Journal of Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 101:1-2, s. 53-65
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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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| 6. |
- Zhang, Qiang, et al.
(författare)
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Spatial and temporal variability of precipitation maxima during 1960-2005 in the Yangtze River basin and possible association with large-scale circulation
- 2008
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 353:3-4, s. 215-227
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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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| 7. |
- Zhang, Zengxin, et al.
(författare)
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Atmospheric moisture budget and floods in the Yangtze River basin, China
- 2009
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Ingår i: Journal of Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 95, s. 331-340
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we explored the trends of the atmospheric moisture budget, precipitation, and streamflow in summer during 1961 to 2005 and possible correlations between them by using the linear regression method in the Yangtze River basin, China. The results indicate that: (1) increasing tendencies can be detected in the atmospheric moisture budget, precipitation and streamflow in the Yangtze River basin; however, the significant increasing trends occur only in the atmospheric moisture budget and precipitation in the middle and lower Yangtze River basin; (2) both the ratio of summer moisture budget to annual moisture budget and the ratio of summer precipitation to annual precipitation exhibit a significant increasing trend in the Yangtze River basin. The ratio of summer streamflow to annual streamflow is in a significant increasing trend in Hankou station. Significant increasing summer precipitation can be taken as the major controlling factor responsible for the higher probability of flood hazard occurrences in the Yangtze River basin. The consecutively increasing summer precipitation is largely due to the consistently increasing moisture budget; (3) the zonal geopotential height anomaly between 1991 and 2005 and 1961 and 1990 is higher from the south to the north, which to a large degree, limits the northward propagation of the summer monsoon to north China. As a result, the summer moisture budget increases in the middle and lower Yangtze River basin, which leads to more summer precipitation. This paper sheds light on the changing properties of precipitation and streamflow and possible underlying causes, which will be greatly helpful for better understanding of the changes of precipitation and streamflow in the Yangtze River basin.
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| 8. |
- Li, Lu, et al.
(författare)
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Validation of a new meteorological forcing data in analysis of spatial and temporal variability of precipitation in India
- 2014
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Ingår i: Stochastic environmental research and risk assessment (Print). - : Springer Science and Business Media LLC. - 1436-3240 .- 1436-3259. ; 28:2, s. 239-252
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Tidskriftsartikel (refereegranskat)abstract
- During the past two decades, numerous datasets have been developed for global/regional hydrological assessment and modeling, but these datasets often show differences in their spatial and temporal distributions of precipitation, which is one of the most critical input variables in global/regional hydrological modeling. This paper is aimed to explore the precipitation characteristics of the Water and Global Change (WATCH) forcing data (WFD) and compare these with the corresponding characteristics derived from satellite-gauge data (TRMM 3B42 and GPCP 1DD) and rain gauge data. It compared the consistency and difference between the WFD and satellite-gauge data in India and examined whether the pattern of seasonal (winter, pre-monsoon, monsoon and post-monsoon) precipitation over six regions [e.g. North Mountainous India (NMI), Northwest India (NWI), North Central India (NCI), West Peninsular India (WPI), East Peninsular India (EPI) and South Peninsular India (SPI)] of India agrees well for the gridded data to be useful in precipitation variability analyses. The multi-time scale of precipitation in India was analysed by wavelet transformation method using gauged and WFD precipitation data. In general, precipitation from WFD is larger than that from satellite-gauge data in NMI and Western Ghats region whereas it is smaller in the dry region of NWI. Both WFD and satellite-gauge datasets underestimate precipitation compared to the measured data but the precipitation from WFD is better estimated than that from satellite-gauge data. It was found that the wavelet power spectrum of precipitation based on WFD is reasonably close to that of measured precipitation in NWI and NCI, while slightly different in NMI. It is felt that the WFD data can be used as a potential dataset for hydrological study in India.
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| 9. |
- Yang, Tao, et al.
(författare)
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Regional frequency analysis and spatio-temporal pattern characterization of rainfall extremes in the Pearl River Basin, China
- 2010
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 380:3-4, s. 386-405
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a method for regional frequency analysis and spatio-temporal pattern characterization of rainfall-extreme regimes (i.e. extremes, durations and timings) in the Pearl River Basin (PRB) using the well-known L-moments approach together with advanced statistical tests including stationarity test and serial correlation check, which are crucial to the valid use of L-moments for frequency analysis. Results indicate that: (1) the entire Pearl River Basin (40 sites) can be categorized into six regions by cluster analysis together with consideration of the topography and spatial patterns of mean precipitation in the basin. The results of goodness-of-fit measures indicate that the GNO, GLO, GEV, and PE3 distributions fit well for most of the basin for different HOM regions, but their performances are slightly different in term of curve fitting; (2) the estimated quantiles and their biases approximated by Monte Carlo simulation demonstrate that the results are reliable enough for the return periods of less than 100 years; (3) excessive precipitation magnitude records are observed at Guilin region of Guangxi Province and Fogang region of Guangdong Province, which have sufficient climate conditions (e.g. precipitation and humidity) responsible for the frequently occurred flood disasters in the regions. In addition, the spatial variations of precipitation in different return periods (Return period = 1, 10, 50 years to 100 years) increase from the upstream to downstream at the regional scale; (4) the seasonal patterns of precipitation extremes for different topographical regions are different. The major precipitation events of AM1R, AM3R, AM5R and AM7R in regions of low-elevation in lower (south-eastern) part of the basin occur mainly in May, June, July and August, while the main precipitation periods for the mountainous region upstream are June, July and August. Further analysis of the NCAR/NCEP reanalysis data indicates that the eastern Asian summer monsoon and typhoons (or hurricanes) are major metrological driving forces on the precipitation regimes. Additionally, topographical features (i.e. elevation, distance to the sea, and mountain’s influences) also exert different impacts on the spatial patterns of such regimes. To the best of our knowledge, this study is the first attempt to conduct a systematic regional frequency analysis on various annual precipitation extremes (based on consecutive 1-, 3-, 5-, 7-day averages) and to establish the possible links to climate pattern and topographical features in the Pearl River Basin and even in China. These findings are expected to contribute to exploring the complex spatio-temporal patterns of extreme rainfall in this basin in order to reveal the underlying linkages between precipitation and floods from a broad geographical perspective. (C) 2009 Published by Elsevier B.V.
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| 10. |
- Zhang, Zengxin, et al.
(författare)
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Evaluating the non-stationary relationship between precipitation and streamflow in nine major basins of China during the past 50 years
- 2011
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 409:1-2, s. 81-93
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the trends of the annual streamflow and precipitation and cross correlations between them were analyzed in nine large river basins of China during 1956-2005. The results indicate that: (1) the annual mean streamflow decreases in arid and semi-arid regions of north China; however, increasing trends occur in south and Southwest China; (2) the annual streamflow and precipitation exhibit reasonable correlation in nine large river basins except those located in inland areas. The annual streamflow over most areas of China is fed by precipitation; however, the decline in streamflow is faster than the decreases of precipitation since 1970s in the arid and semi-arid regions of north China. The relationship between the annual precipitation and streamflow presents a non-stationary state in north China. This non-stationary relationship is strongly influenced by both human activities and precipitation changes; (3) a significant increase of water use might be the major factor responsible for the steeper decline in streamflow than in precipitation in Haihe River, Yellow River and Songliao River basins in north China. In inland river areas, increase of water use and actual evapotranspiration might result in decline in streamflow although precipitation has an increase tendency. This paper sheds light on the non-stationary relationship between annual precipitation and streamflow and possible underlying causes, which will be helpful for a better understanding of the changes of precipitation and streamflow in China at large scale and in other regions of the world.
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