Hello, everyone, this is Liu Chang (D3) writing about some ideas of our research. It has been really a long time since my last blog, which was usually about trips or conferences outside of Tokyo. Because of the COVID-19, everything has been changed, and now we are getting used to on-line meeting and discussion. Likewise, sometimes, the sudden change (e.g., war, disaster, pandemic) will alter the society and shape it to a form we’ve never imagined before. Our research, which focuses on the historical flood of China, is also related to this topic in a general concept. How had these extreme events shaped the society? How will it change our life in the future? Maybe it’s better to find answer from history. As the saying goes, to look forward, while looking backward. As a hydrologist, my perspective will be mainly about historical flood event and the interactions between environment and society.
First, I would like to introduce a little bit about the background of our target area: the Yangtze River basin. 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.
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| Fig.1. Refugees after 1931 flood (from newspaper) |
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| Fig.2. Refugees in Hankou City (from newspaper) |
Similar flood occurred again in 1954, resulting in 31,762 deaths, damages to 18.9 million people and 31.7 billion m2 farmland. On the contrary to the severity of these flood events, are the ignorance of our knowledge about it. For example, the flood propagation process, the damage of each prefecture is still unclear in most region. The first step of my journey to the history will be to reconstruct the flood event using modern techniques. But the biggest difficulty of reconstructing a flood event 90 years ago is the scarcity of data. Luckily, with the help from historians (thanks to Prof. Shiroyama), we’ve collected precipitation data and discharge data since 1870. With a lot of calibration and validation, the inundation condition is reproduced for 1931 and 1954 flood
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| Fig.3. Inundation area of 1931 flood |
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| Fig.4. Inundation area of 1954 flood |
Then, with the reproduced inundation data, we could finally have a glance of the flood process of 1931 and 1954. In 1931, the flood was widely inundated across the mid-reach to lower-reach of Yangtze River (Fig.3). On the contrary, with the detention basin (the orange polygons) and levee construction in 1950s, the flood was controlled at a certain level in 1954 (Fig.4). Moreover, with these data, we’ve calculated the damage condition of these two events (Fig.5). Finding out that previous statistic of 1931 was underestimated, and the real condition might be much worse than imagined.
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| Fig.5. Inundated farmland area of 1931 and 1954 |
With these data, one must keep wondering, what has been changed by these terrible floods? Is the life of the locals also suffered as we do today because of COVID-19? If you’re familiar with the Chinese history, you may also wonder, what has the alteration of society (the benchmark is the establish of PRC) affected the flood countermeasures? These questions have brought us to investigate into the social-hydrological interactions, which is a charming and challenging field we are still working on.
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| Fig.6. Conceptual framework of 1931 |
To shed light on the complex system consisted of both society and hydrology, we’ve built a qualitative model called conceptual framework (Fig.6). Through which, the complicated connection was simplified to three parts: top-down, bottom-up and flood impact. The idea is to capture important connections of parameters and later test the system with designed shock (e.g., social alteration). Hopefully, we could not only deepen the understanding of historical thread of social-hydrological change but also predict the future reaction of the complex system.
Last but not least, our research is on-going and we are open to innovative ideas and thoughts. If you’re interested, don’t hesitate to visit our website and contact us!
Lab website: http://aqua.t.u-tokyo.ac.jp/REEL/index.html
Project website: https://www.hysoc.e.u-tokyo.ac.jp/
