Demographic impact of climate change on northwestern China in the late imperial era
Introduction
The societal impact brought by global climate change has received international attention. In recent years, a growing body of quantitative studies (i.e., large-N study) has examined the impact of climate change on historical agrarian China. Their basic premise is that “in the pre-industrial period, the main source of livelihood was agriculture; traditional agriculture was very much dictated by the whims of climate and weather conditions; any deterioration of climate would trim agricultural production; yield reduction would trigger famine, tax revolt, and a weakening of state power; the deficit in livelihood resources was aggravated by the population expansion accumulated in the previous favorable climate. Thus, human crises were likely to erupt during the period of deteriorating climate” (hereafter climate–man nexus) (Lee and Zhang, 2015, p.237). Along with this rubric of research, several aspects of Chinese societies have been correlated with climate change, such as armed conflicts (Zhang et al., 2005, Zhang et al., 2006, Zhang et al., 2007b, Zhang et al., 2010, Zhang and Lee, 2010, Jia, 2013), epidemics (Pei et al., 2015b), migrations (Pei and Zhang, 2014, Pei et al., 2016a), agricultural production (Yin et al., 2015), economic fluctuations (Wei et al., 2014, Wei et al., 2015b, Wei et al., 2015a, Pei et al., 2016b), geo-politics (Zhang et al., 2015), and population growth dynamics (Lee et al., 2008, Lee et al., 2009, Lee and Zhang, 2010a, Lee and Zhang, 2013, Lee, 2014). The above studies demonstrate the adverse socio-economic and demographic effects brought by climate deterioration (cooling in particular) via statistical means, shedding light on the role of global climate change in shaping Chinese history in a macro-historical perspective.
Nevertheless, the findings of the above studies are also subject to debate. One of the key issues is that the dominant approach of the abovementioned studies is to take the whole of China as a spatial aggregate, assuming the vast territory of China to be uniform. However, the impact of climatic forcing may be buffered by various political, socio-economic, and technological institutions, at least in some places and in some instances (Fan, 2010). Crisis occurs only if the forcing exceeds the buffering capacity of human society (in terms of migration, economic change, innovation, trade, peaceful resource redistribution, and so on) for a significantly long period. Also, in regions where population pressure and agricultural dependence on climate were less important, the climate–man nexus was weaker and less apparent (Zhang et al., 2007a, Zhang et al., 2011a). As the socio-economic context, such as population pressure and agricultural dependency that characterizes institutional capacity to adapt to social pressure, varies across places, the societal impact brought by global climate change may be regionally diversified. As highlighted by Catto and Catto (2004), in some regions, climate change has been a driving force of social crises; in other regions, the climate has played an important supporting role. In addition, there are also regions where the effect of climate change is secondary.
Owing to the above concern, a scholarly attempt has been made to scale down the quantitative analysis of the historical climate–society nexus to smaller geographic regions in China. The roles of regional geographic context and cultural factors in mediating the nexus have also been highlighted (Pei et al., 2016a). Yet, the attempt is characterized by strong regional bias. Even though the historical climate–man nexus in eastern China (Zhang et al., 2007b, Bai and Kung, 2011) and northern China (Kung and Ma, 2014, Chen, 2015) has been repeatedly examined, the one in northwestern (NW) China still remains poorly investigated. So far, only the frequency of natural disasters (Lee and Zhang, 2010b, Lee and Zhang, 2011, Lee and Zhang, 2012) in relation to climate change has been quantitatively explored. A related line of research is about using archaeological records to trace the changes of subsistence strategy, human settlement pattern, and culture in different climatic episodes (Dong et al., 2012a, Dong et al., 2012b, Dong et al., 2013a, Dong et al., 2013b, Jia et al., 2012, Jia et al., 2016a, Jia et al., 2016b, Guan et al., 2014, Jia et al., 2016c, Jia et al., 2016d, Zhou et al., 2016) as well as the human impact on the bio-physical environment (Zhou et al., 2012, Zhao et al., 2013, Ren et al., 2015). Given that some important historical events with disastrous social and demographic consequences, such as late Ming peasant rebellions (c. early seventeenth century) and the Dungan Revolt (c. 1862–1877 and 1895–1896), originated in NW China, and that they may have been triggered by deteriorating climate (Zheng et al., 2014), the historical climate–man nexus in NW China is worth exploring, particularly in a quantitative manner.
The present study seeks to fill the abovementioned research gap. As various aspects of human societies (e.g., armed conflicts, epidemics, migration, and so on), which are covered in the previous climate–man studies, are eventually linked to population growth dynamics (Lee and Zhang, 2010a, Lee and Zhang, 2013, Lee, 2014), we focus on the extent to which periodic fluctuation of temperature and precipitation affected population checks, and subsequently population growth dynamics, in NW China in recent human history.
Section snippets
Study area and study period
NW China includes the current provinces/autonomous regions of Sha'anxi, Gansu, Ningxia, Qinghai, and Xinjiang, comprising about one-third of China's land area. It is also the region where the Hexi Corridor is located and was of significant military importance to ancient China (Li, 1998). Its total area is 3.09 million km2, and it overlaps with the fringe of the monsoon limit, where the precipitation regime is simultaneously influenced by multiple atmospheric circulation systems, such as Asian
Overall picture of the climate–man nexus in NW China
In terms of the counts of positive checks, two periods are revealed to be chaotic periods in NW China in our study time span: AD 1600–1700 and AD 1850–1911. NW China was also characterized by frequent natural disasters and social instability in the above periods (Jiang, 1993, Yuan, 1994). Subject to frequent positive checks, total population size was stagnated and only increased by 3.85% in AD 1578–1661, from 10.8 to 11.2 million, while total population size dropped by 43.71% in AD 1820–1912,
Drought anomalies and the climate–man nexus
Population growth is constrained by food subsistence. When population growth overshoots the available subsistence, poverty and consequently positive checks occur (Malthus, 1798). In the pre-industrial era, subject to the low level of technology, agricultural production and subsistence strategies were largely contingent upon climatic conditions (Galloway, 1986, Jia et al., 2016a, Jia et al., 2016b, Jia et al., 2016c, Jia et al., 2016d). Such climate dependence also shaped human settlement
Conclusions
Drought anomalies, which are a proxy of precipitation change, were imperative in driving various positive checks in Sha'anxi, Gansu, and Ningxia, NW China in the late imperial era at the multi-decadal time-scale, while their connection was, in part, mediated by government policies. Even though drought anomalies were the important stressor, drought itself is often modulated by temperature change in NW China (Lee and Zhang, 2011, Lee et al., 2015a). Therefore, the influence of temperature should
Acknowledgements
This research was supported by the Hui Oi-Chow Trust Fund (201502172003), Research Grants Council of The Government of the Hong Kong Special Administrative Region of the People's Republic of China (HKU758712H, HKU745113H, and 17610715), China National Science and Technology Basic Work Program (2012FY111700), and the CAS/SAFEA International Partnership Program for Creative Research Teams. We also thank Aslak Grinsted and Eric K. W. Ng for providing the computing code for the wavelet coherence
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