1736-1911年中国水灾多发区分布及空间迁移特征

重建历史时期极端气候灾害的时空格局,对于认识当前和未来的灾害演变趋势,辨识灾害高风险区,更好地应对气候变化的挑战具有重要意义。本文基于《清史·灾赈志》中的历史水灾记录,以县级政区为单元,逐年提取了1736-1911年间中国境内的8582个水灾发生地点;利用核密度估计法对这一时期及3个特征时段(1736-1795、1796-1850和1851-1911年)的水灾空间分布特征进行分析,并结合风险理论框架讨论水灾多发区的分布及迁移的影响因素。主要结论如下：①1736-1911年水灾多发区主要集中在华北平原北部的海河、黄河下游,淮河下游,长江中下游三大平原及沿江地带,与现代分布格局存在一定差异;②华北平原北部是清代水灾最为集中的区域,这与当时华北平原降水偏多有关,而进入19世纪后,当地社会经济系统的高脆弱度也大大加重了灾情;特别是1855年黄河改道后,因政府应对不力,使得1851-1911年间鲁西北地区沿黄河下游河道出现一个条带状水灾多发区;③19世纪长江中下游地区水灾频次激增,其原因除梅雨变化导致的极端降水事件增多外,人类不合理的农业开发活动大量挤占湿地和水体,也在相当程度上增大了当地面对水灾时的物理暴露度。

Spatiotemporal distribution of high flood risk areas in China, 1736-1911

The reconstruction of spatiotemporal distribution of extreme climatic disasters in the past is important for the identification of high risk zones at present, the prediction of change in the future, and improved response to the challenges of climate change. In this study, information about historical floods was extracted from the Qing History, and counties suffered from floods during 1736-1911 were identified year by year, which sum to 8,582. Using the kernel density estimation method, spatial distribution of hotspots where floods occurred frequently during 1736-1911 was reconstructed, and the spatial differences among three periods (1736-1795, 1796-1850, and 1851-1911) were analyzed with the theoretical framework of disaster risk developed by the Intergovernmental Panel on Climate Change (IPCC). It is found that the main high risk areas during 1736-1911were the lower reaches of the Yellow River and the Hai River on the North China Plain, the lower reach of the Huai River, and the three great plains (Jianghan-Dongting Lake, Poyang Lake, and Tai Lake) in the middle-lower Yangtze River Basin and riparian areas, and the spatial pattern of floods was slightly different from the modern time. The lower Yellow River and Hai River were the most significant hotspots where floods were concentrated. It was partly because in the 18th and the 19th centuries the annual precipitation in the North China Plain was more than the 20th century, and the high vulnerability of regional socioeconomic system throughout the 19th century also played a negative role in damage control. After the Yellow River changed its course in 1855, new levees were not built until the 1870s because of social unrest and financial crisis, which led to a new high risk area with a banding distribution along the course of the Yellow River in northeast Shandong Province. In the 19th century, flood occurred much more frequently in the middle-lower Yangtze River Basin than the 18th century. On the one hand, due to the change of Meiyu, extreme precipitation events significantly increased in the area; on the other hand, inappropriate agricultural development (such as diked field) led to rapid disappearance of natural wetlands and lakes, which meant higher water level in flood period and more exposure to flood.