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

本项目旨在编纂洪水历史，并利用过去的气候资料和地质资料，重建与亚洲季风变化有关的过去气候和环境。在百年时间尺度上，长江流域夏季风降水在1700年、4200年和6200年前后均有所增加。在日本中部的熊舟河流域，大约在6000年前发现了快速沉积，那么这一时期可能经常发生大规模的洪水。通过对日本西南部石垣岛珊瑚岩心的分析，重建了过去的盐度。在上世纪后半叶的变化中，孟加拉国布拉马普特拉河河道的移动在年代际时间尺度上出现了接近和远离平衡条件的变化。孟加拉国的严重洪灾造成了夏季季风季节水稻种植的严重产量损失，而严重洪灾后的旱季水稻产量大幅增加，以弥补洪水造成的损失。尼泊尔的降雨特征位于流入孟加拉国的河流的上部集水区，发现尼泊尔的强降雨发生与孟加拉国的严重洪水发生并不对应。在日本，由于全球气候变暖，最近冬季的结束和白雪皑皑的开始和结束都有所推迟。此外，在气候变化研究中常用的NCEP/NCAR再分析数据中，也发现了中国内陆地区的系统误差。因此，不建议将此数据用于东亚地区的长期气候变化研究。

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.