[M-IS22] History X Earth and Planetary Science

[MIS22-07] The interactions between floods and agricultural society in modern Chinese history: a case study based on 1931 and 1954 floods

*CHANG LIU¹, Akiyuki Kawasaki², Tomoko Shiroyama³ (1.Department of Civil Engineering, the University of Tokyo, 2.Institute for Future Initiatives, the University of Tokyo, 3.Graduate School of Economics, the University of Tokyo)

Keywords:Chinese modern history, Yangtze River Basin, flood damage, society changes, socio-hydrology

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 the deadliest floods ever recorded in Chinese history, causing 422,499 deaths. Just after 23 years, another flood occurred again in 1954, resulting in 31,762 deaths. Although we have found that 1954 flood being larger and higher compared to 1931 flood, 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 based on historical narratives. 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 digized rainfall records. 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. On the contrary, the total increase of influence farmland in 1954 is around 50% after modification, indicating certain progress 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 indicated that the countermeasures against 1954 flood being more successful than 1931 flood case. Moreover, the changes of agricultural interactions with floods have also been estimated using the potential crop production (PCP), showing an improvement in disaster mitigation in 1954. Finally, an agent based model was constructed to simulate such change and its impact on flood response. Our results demonstrate how agricultural society changes affect the response towards natural hazards from a historical perspective, the knowledge of which is likely to be applicable to many other regions and times.