The Interactions Between Flood Disaster and the Agricultural Society Change in Yangtze River Basin: A Case Study of 1931 and 1954 Floods

As the longest river in Asia, the Yangtze River has shown its impact on human societies with floods recorded since 12th 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 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 fewer casualties, especially when there being no significant progress in the countermeasure techniques. To answer this question, here we propose a conceptual socio-hydrological framework within which the mutual influence between agricultural society and water system is analyzed. We found that before and after 1931 flood, a change of social structure of villages aggravated the vulnerability of agricultural production towards natural hazards, and hydrological extremes speeded-up such structure change afterwards. As for 1954 flood, remolding of village structure strengthened the resilient ability to a certain degree, while the damage was controlled at the cost of rural settlements. Furthermore, to quantitatively analyze the effect of such society change, a model-derived index called Potential Crop Production (PCP) is developed. The PCP analysis indicates 1954 being more successful than 1931 in securing rice production, with an increase of 13% compared to a decrease of 26% of observed rice yield respectively. Our results demonstrate how the qualitative conceptual framework together with the quantitative PCP are likely to help comprehend the socio-hydrological correlation of a pre-industrial society like the 20th century China. We anticipate our study to be a starting point for more sophisticated socio-hydrological models, which will likely to be applicable to many other regions and times.