Suitable planting areas for winter wheat in north China are expected to shift northwardly due to climate change, however, the increasing extreme events and the deficiency of water supply are threatening the security of planting system. Thus, based on predicted climate data for 2021–2050 under the SSP1-2.6, SSP3-7.0, and SSP5-8.5 emission scenarios, as well as historical data from 1961–1990, we use four critical parameters of percentage of extreme minimum temperature occurrence, first day of the overwintering period (FD), sowing date (SD), and precipitation before winter (PBW) to determine the planting boundary of winter wheat. The results show that, the frequency of extreme minimum temperature occurrence is expected to decrease in the North winter wheat area, which will result in a northward movement of the western part of northern boundary by 73, 94, and 114 km on average, as well as FD delays ranging from 6.0 to 10.5 days. Moreover, the agrometeorological conditions in the Huang-Huai winter wheat area are expected to exhibit more pronounced changes than the rest of the studied areas, especially near the southern boundary, which is expected to retreat by approximately 213, 215, and 233 km northwardly. The north boundary is expected to move 90–140 km northward. Therefore, the change in southern and northern boundaries will lead the potential planting areas of the entire North winter wheat area to increase by 10,700 and 28,000 km2 on average in the SSP3-7.0 and SSP5-8.5 scenarios but decrease 38,100 km2 in the SSP1-2.6 scenario.

Based on historical records and crop harvest scores extracted from historical documents, this study reconstructed the spatial-temporal distribution and severities of floods in the Yangtze-Huai River valley in 1823 and 1849. We also summarized the effects of the floods on society and identified government measures taken to cope with the floods in the context of the economic recession in the period of 1801--1850. The 1823 flood, which was caused by the heavy precipitation of the Meiyu period and typhoons, severely affected areas in the lower reaches of the Yangtze River. Meanwhile, the 1849 flood, triggered by long-term, high-intensity Meiyu precipitation in the middle and lower reaches of the Yangtze River, mainly affected areas along the Yangtze River. The 1849 disaster was more serious than the one in 1823. In the lower reaches of the Yangtze River, the 1849 flood caused the worst agricultural failure of the period 1730--1852. To deal with the disasters, the Qing government took relief measures, such as exempting taxes in the affected areas, distributing grain stored in warehouses, and transferring grain to severely afflicted areas. These relief measures were supplemented by auxiliary measures, such as exempting commodity taxes on grain shipped to disaster areas and punishing officials who failed to provide adequate disaster relief. The flood disasters disrupted the water system of the Grand Canal and forced the Qing government to transport Cao rice by sea beginning in 1826. This laid the groundwork for the rise of coastal shipping in modern China. With the economic recession of the 19th century, Chinese society was not as resilient to floods as it was in the 18th century. Compared to droughts, floods are more difficult to deal with and pose greater threats to infrastructure and to normal life and work in the cities.