Climatic and sociocultural changes may have contributed significantly to the demise of the Tang dynasty by weakening border defenses.
Image Credit: Scientific Frontline
Scientific Frontline: "At a Glance" Summary
- Main Discovery: Hydroclimatic instability, characterized by extreme droughts and floods between 800 and 907 CE, functioned as a critical driver in the socio-political collapse of the Tang Dynasty.
- Methodology: Researchers reconstructed historical runoff behavior in the Yellow River basin by analyzing long-term tree-ring data archives to model local hydroclimatic trends during the 9th century.
- Specific Mechanism: Vulnerability to climate extremes was exacerbated by an agricultural shift from drought-resistant millet to water-intensive wheat and rice, resulting in uncompensated crop failures during dry periods.
- Systemic Consequences: Compounded by collapsed supply corridors, widespread malnutrition weakened northern border defenses and precipitated mass migration southward, destabilizing the empire's political structure.
- Significance: The study establishes a historical precedent for how environmental stressors, when intersecting with specific socio-cultural choices, can trigger irreversible tipping points in complex societal systems.
Environmental phenomena and their consequences can disrupt social structures and destabilize political systems. An interdisciplinary research team demonstrated this using the example of the late Tang dynasty in medieval China.
Migration and mobility due to climate change are nothing new. This is suggested by an interdisciplinary study in which researchers from the University of Basel were also involved. They investigated how hydrological extremes such as droughts and floods between 800 and 907 CE in particular affected society and politics in China. They report on their findings in Communications Earth and Environment.
This period is interesting because it marked the decline of the Tang dynasty, which had existed since 618 CE and is considered a cultural high point in China’s history, with a sophisticated administrative system and a flourishing culture. The study focuses on the region around the Huanghe river (Yellow River) in northern China. Using climate proxy data, they determined trends in how the local climate changed in the 9th century CE.
Tree rings as contemporary witnesses
Tree rings, for example, provide clues about the climate. Their condition indicates whether a year was dry or rainy: in years with high precipitation, trees grow faster, and the tree rings are further apart than in dry years. The older a tree is, the further back this data archive goes.
The researchers used existing long-term tree-ring data records from the Yellow River basin. The reconstructed runoff behavior served as an indicator for hydroclimatic models, especially for the upper courses of the river. “The runoff eventually reaches further downstream and influences the amount of water available, for example for irrigating the fields,” says the study’s first author Michael Kempf, who has since moved from the University of Basel to the University of Cambridge.
Fatal changes in agriculture
Based on their analyses, the researchers conclude that climatic changes and an increase in extreme weather events were key factors in the collapse of the Tang dynasty in 907 CE. Increased droughts and floods took their toll on the soldiers tasked with protecting the empire’s outer borders and their families against invasive troops from across the borders.
“Hydroclimatic extremes have a very direct influence on crop failure and grain storage conditions,” says Kempf. Seed shortages and increased food demand quickly pushed supply systems to their limits. A bad year therefore also had consequences for the future.
The situation was further exacerbated by the choice of cereal crops: people increasingly favored the cultivation of wheat and rice over millet. Kempf can only speculate the reasons for the agricultural change. Perhaps millet was considered a less prestigious food than wheat and rice. However, these are less climate-resistant than drought-resistant millet and require more water to grow. “As long as there is enough water, this is not a problem, but during prolonged dry periods, shortages occur.” Millet cultivation could perhaps have cushioned these negative effects. As it was, however, the risk of crop failures and famines increased.
These losses could not easily be compensated for by shipments from other parts of the country. This was also because droughts and floods affected supply routes and supply corridors collapsed.
Fleeing from hunger
The malnutrition of the population may ultimately have led to the collapse of border defenses in the north of the empire. “Of course, people were weakened and therefore more vulnerable. Due to the military pressure on the outer border regions, they migrated south, where they believed they would find better conditions,” says Kempf. “This led to political destabilization and is likely to have contributed to the demise of the Tang dynasty.”
However, Kempf emphasizes: “Our results are approximations. The actual conditions at that time cannot be reconstructed with certainty. It’s a complex interplay of many different factors.”
The study concluded that socio-cultural and climatic changes can lead to tipping points in the system because the balance is disrupted. This is a development that could occur more frequently in view of climate change today.
Published in journal: Communications Earth and Environment
Authors: M. Kempf, M. L. C. Depaermentier, R. N. Spengler III, M. D. Frachetti, F. Chen, J. Luterbacher, E. Xoplaki, and U. Büntgen
Source/Credit: University of Basel | Noëmi Kern
Reference Number: es011526_01