| The process of human beings grabing resources from the nature has changed the original state of the Earth system. Meanwhile, the Earth system has been in its long-term evolution, with its inherent cyclical and developing laws. The interpretation of both results in the environmental changes. Exploring the impact of environmental change on the water cycle and water resources has become a hotspot research and focus. With Yangtze River basin and hundreds of basins in the contingous United States as study areas, extreme precipitation indices, flood hazard and its risk, the links and similarity between flood frequency and water balance at different time scales, future runoff changes of the Yangtze River were analyzed in this study at the aim of exploring the responses of hydrological extreme events and water budget to the environmental change. The main research achievements and innovations of this study are summarized as follows:(1) A series of extreme precipitation indices (EPI) was chosen from angles of precipitation magnitude, intensity and persistence, to analyze the historical trends and future change of EPI of the Yangtze River basin. None of the chosen EPI shows comprehensively significant increasing or decreasing trends during the historical period. During the first half of the21st century, the vast majority of nine EPI show a mixed pattern of increasing and decreasing trends. Strong correspondence between changes in EPI and greenhouse gas emission concentration was found and the magnitude of heavy precipitation indices and drought indices increases at the same time in the lower region of the Yangtze River basin.(2) The practical performance in downscaling precipitation of ASD and Lars-WG statistical downscaling method has been compared. Multi-model ensemble was used to reduce the impact of the uncertainty caused by climate models. Sensitivity parameters of future changes in runoff were calculated respectively according different forms of Budyko curves. The dominant factors affecting the future runoff of Yangtze River basin vary for the three periods.(3) A flood control risk analysis model and the multi-input and single-output system model were set up to calculate the risk of excessive flood occurring at middle section of Yangtze River. The results show that the scheme of impounding water in advance for the Three Gorges Reservoir does not increase flood control risk in the middle Yangtze River reach. Two indices were proposed to quantitatively evaluate the hazard caused by flood combinations for the Poyang Lake basin.(4) Two different measures of mean annual water balance, aridity index (AT) and base flow index (BFF), extracted from MOPEX dataset, refer to the process controls on behalf of climatic and landscape conditions, and AI has a first order control on both the mean and coefficient of variations (Cv) of annual maximum floods while BFI appeared to be a second order control on the magnitude and shape of the flood frequency curve. The results provide an innovative means to delineate homogeneous regions within which the flood frequency curves can be assumed to be functionally similar. At another level, understanding the connection between annual water balance and flood frequency will be another building block towards developing comprehensive understanding of catchment runoff behavior in a holistic way.(5) By redefining the aridity index, a statistical relationship between annual aridity index and annual maximum flood was established, which was revealed as a symmetrical pattern existing "between basins" and "between years". Significant increasing relationship was found between different seasonality indices that represents annual maximum extreme events and water balance, respectively. From the compassion between wet and dry years devided by aridity index, the annual maximum flood of dry years shows stronger seasonal characteristics. The spatial-temporal symmetry of the relationship bwtween drought index and seasonal indicators were not found. |
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