Climate change and human migration in historical China over the past two millennia

Climate change-driven migration has drawn serious attention, especially in the background of the current global warming. Surprisingly, in history, climatic impacts in relation to human migration in the long term and on the large spatial scale have been academically neglected. Even there are some related works; most of them are Eurocentric and qualitative analysis. Consequently, the importance of climate change in driving migration remains ambiguous. This research seeks to quantitatively explore how far climatic impact has on human migration in China from 221 B.C. to A.D. 1911. This research distinguishes itself from the others in a way that it principally relies on all known cases instead of some selected examples to investigate the “climate change-migration” relationship in the long term and on the large spatial scale. A conceptual model is constructed in the study to systematically analyze the relationship between climate change and migration in historical China. The study hypothesized that long-term cooling and drying shrink the land carrying capacity, which lead to the occurrence of social disasters. Mass migration then happens to escape from these social disasters. Fine-grained climate, social disasters, migration, population and other socio-economic datasets have been chosen and various statistical methods have been essentially applied to verify the proposed conceptual model, supplemented with qualitative analysis. In the study, scale thinking as a key methodological issue is highlighted. The results of this study are closely associated with different scales in time and space. On the national scale, the study quantitatively proves that climate change is the fundamental cause of migration in the long term. Meanwhile, if climate changes, migration to the south (more specifically southeast) will be preferred, which results that population center also moves southward/eastward. On the regional scale, climate change could directly result in the migration of north nomadic minorities. As a long-term trend, precipitation is more important than temperature in driving to north pastoralists’ migration. Besides, more southward migration occurs during drought and cooling in pastoral and wheat zone of China, while in rice zone with high levels of rainfall and temperature, migration directions are not totally restricted by climate change. On the provincial scale, emigration leads to the population size/density decrease in Xinjiang, Qinghai and Jiangsu Provinces. However, immigration in Inner Mongolia, Shaanxi, Sichuan (including Chongqing City), Zhejiang, Jiangxi, Guangdong, Yunnan, and Taiwan Provinces could increase population size/density during the entire study period. In summary, the “climate change-migration” relationship in historical China in the long term and on the large spatial scale is first time verified, particularly in a quantitative manner. Meanwhile, this study is the first to quantitatively support the scale thinking by statistical evidences of research findings at different scales. Furthermore, the “Push-Pull” theory and two schools of causality relationship that is “historical laws (statistical causality) versus INUS causality” have been re-evaluated under the scale thinking. The research on migration under the climatic impact in the past long history will potentially help to anticipate and interpret the certain cases of human movement caused by current climate change.published_or_final_versionGeographyDoctoralDoctor of Philosoph