History of floods, and long-term climatic and environmental changes in Asian monsoon region

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This project aimed at compiling the history of floods, and reconstruct the past climate and environment related to Asian monsoon variations by utilizing past climatic data as well as geological data.As for the centennial time scale variations, it was revealed that summer monsoon rainfall in the Yangtze River basin increased in about 1,700,4,200 and 6,200 years ago. In the Kumozu River basin in central Japan, rapid deposition was found in about 6,000 years ago, then large-scale floods may have often occurred in this period. By the analysis of the coral core obtained at Ishigaki Island in Southwest Japan, past salinity was found to be reconstructed.As for the variations in the latter half of the past century, the shift of river channels in Brahmaputra River, Bangladesh occurred to be close to and apart from the equilibrium conditions in decadal time-scale. Severe floods in Bangladesh caused serious production loss in the rice cultivation during the summer monsoon season, while the dry season rice production after the severe floods was found to substantially increased to compensate the loss by the floods. The rainfall characteristics in Nepal located in the upper catchment area of the rivers flowing into Bangladesh, it was found that the heavy rainfall occurrences in Nepal were not corresponded to the severe floods occurrences in Bangladesh. In Japan, recently delay of the end of winter, onset and end of Baiu is found under the global warming. Also found is the systematic error in the NCEP/NCAR reanalysis data, popularly used in the climatic change study, over inland China was detected. Thus, it is not recommended to use this data for the long-term climatic change studies over East Asia.