The society interactions with floods in the modern Chinese history: a comparison between 1931 and 1954 floods

As the longest river in Asia, the Yangtze River has shown its impact on human societies with floods recorded since 12^th century. In 1931, the Yangtze River has manifested its force again with one of the deadliest floods ever recorded in Chinese history, causing 422,499 deaths, damages to more than 25.2 million people and 58.7 billion m² farmland. Similar flood occurred again in 1954, resulting in 31,762 deaths, damages to 18.9 million people and 31.7 billion m² farmland. Researches have shown that 1954 flood being larger and higher compared to 1931 flood. However, it is still unclear for what reason that a more severe flood leading to less damage. Was it because of the change of residents’ interactions and for what extent had it affected the damage? To answer this question, first, we constructed a conceptual framework of 1930s and 1950s agricultural society. From which drastic changes has been detected (e.g., increase of absentee landlords, land reform) and the residents’ interactions with floods have been analyzed. Then, we reconstructed the flood inundation process of 1931 and 1954 floods with gauged rainfall dataset. After referring to the investigation report, the inundation information was applied to re-estimate the flood damage on farmland, houses, and residents. With the simulation and modification, we found that the inundated farmland of 1931 is about 83% more than former, indicating a much more severe influence on residents’ lives than we used to think. On the contrary, the total increase of influence farmland in 1954 is around 50% after modification, suggesting a relative success in reducing flood damage. To quantitatively explain it, the countermeasures during 1954 flood were estimated, showing that the reinforcement of levees in 1950s was more effective in reducing inundation area of 7%, while the construction of detention basins accounted for only 2%. Such results revealed that the countermeasures against 1954 flood being more successful than 1931. Moreover, the changes of agricultural interactions with floods have also been estimated using the potential crop production (PCP), indicating an improvement in disaster mitigation in 1954. Our results demonstrate how society changes are likely to affect the response towards natural hazards, the knowledge and method of which are expected to be applicable to many other regions and times.