Climate change and the temporal-spatial pattern of war in imperial China

Abstract

The climate–war relationship has recently attracted great attention in scientific communities, the public and policymakers in the background of global warming. However, studies on such a nexus are incomprehensive because their temporal ranges are mostly limited to the contemporary era. The climate–war association in ancient times is still unclear due to the lack of historical documents in earlier period and the difficulty of text quantification. Under the circumstances, qualitative approach has been widely adopted, although quantitative methods are becoming more and more prevailing. By using inferential statistics, scientists have revealed the mechanism of the climate–war linkage, yet time-series analyses dominate these investigations and spatial statistics and visualization are extremely rare.

This thesis aimed to explore the temporal–spatial distribution of war and its connection to climatic and non-climatic elements in imperial China (214 BC–1911 AD) by employing various temporal and spatial analytical techniques. Battle was regarded as the basic unit of war, and coordinates of each battlefield were retrieved. General war, agri-nomadic conflict and rebellion were defined and visualized within different temperature and precipitation cycles from multidecadal to multicentennial scales. Preliminary results included: (1) Battles clustered in northern China during the early imperial era whereas they massively spread over the south in the late imperial age, which was consistent with the cooling and drying trend throughout the last 2000 years. Hence, the southward movement of battle latitude was more striking than the variation of battle longitude. (2) Directional features showed that a west–east or northwest–southeast axis took the lead in earlier periods, yet it turned into a north–south orientation during later periods. (3) Most battle locations and scopes altered north-/west-/northwestward in warm and/or wet stages but shifted south-/east-/southeastward in cold and/or dry phases, among which the ever-enlarging areas signified the outward expansion of the Chinese Empire over time. (4) The focus of war epitomized by hot spots transferred from the traditional warring zones (i.e., Guanzhong–Central Plain) in warm and/or wet climate to the North China Plain, the Jianghuai region and the lower reaches of the Yangtze River/Yangtze River Delta in cold and/or dry conditions. (5) The synchronous southeastward migration of war–population center overall accorded with the long-term trend of temperature and precipitation, while the center distance, which was used to measure the extent of military expansion, lengthened during warm intervals but varied in wet–dry cycles.

To sum up, the influence of climate on the spatiality of war is indirect owing to the mediation of socioeconomic, demographic and (geo)political factors. Nonetheless, temperature contributes more to battle latitude whilst precipitation affects both battle latitude and longitude, which correspond to the characteristics of climate in China. This work lays a foundation for future studies as researchers may obtain some implications from these findings as well as deepen the understanding of the climate–war relation, and it also suggests that preventive actions should be taken by the governments if global warming continues to intensify.