Floods have been experienced with greater frequency and more severity under global climate change. To understand the flood hazard and its variation in the future, the current and future flood hazards in the 21st century in China are discussed. Floods and their trends are assessed using the accumulation precipitation during heavy rainfall process (AP_HRP), which are calculated based on historical meteorological observations and the outputs of a global climate model (GCM) under three Representative Concentration Pathway (RCP) scenarios. The flood-causing HRPs counted by the flood-causing critical precipitation (the 60% fractile of AP_HRP) capture more than 70% of historical flood events. The projection results indicate that the flood hazards could increase under RCP4.5 and RCP8.5 and increase slightly under RCP2.6 during the 21st century (2011–2099). The spatial characteristics of flood hazards and their increasing trends under the three RCPs are similar in most areas of China. More floods could occur in southern China, including Guangdong, Hainan, Guangxi and Fujian provinces, which could become more serious in southeastern China and the northern Yunnan province. Construction of water conservancy projects, reservoir dredging, improvement of drainage and irrigation equipment and enhancement of flood control and storage capacity can mitigate the impacts of floods and waterlogging on agriculture.

Natural hazards such as floods and droughts occur frequently in southwestern China and have occurred more frequently in recent years, which has caused and will continue to cause serious damage to ecosystems and human lives and property. A full knowledge of the probability of hydro climatic variables is essential for the prevention and mitigation of natural hazards in return. Based on historical archives, atlases and other documented data, a sequence of graded drought and flood disasters covering the period 1250–2000 in Wuzhou City, southwest China, was reconstructed. Then, a correlation coefficient (−0.79, p < 0.01) was established between the sequence of grades and the measured annual precipitation from 1961 to 2000; using this correlation and the sequence of grades from 1250 to 2000, the annual precipitation record (from 1250 to 2000) was reconstructed and extended. Finally, we compared the reconstructed annual precipitation to the measured values from 1961–2000 to evaluate the efficacy of this method. The results show that the reconstructed precipitation sequence is credible, with a high correlation coefficient (0.84, p < 0.01) and a low relative bias (−1.95%). The reconstructed results indicate that the annual precipitation in Wuzhou City increased continuously during the 13–15th century and the 18–19th century and decreased during the 16–17th century and the 20th century. These results are expected to be useful for the prevention of flood and drought impacts and for understanding climate change.