💧 How climate changes led to the fall of a Chinese dynasty

How could extreme climate events contribute to the end of a great civilization? A team of researchers examined this question by focusing on the Tang dynasty, which ruled China between the 7th and 10th centuries.

Their work focused on northern China, a region traversed by the Yellow River, essential for agriculture and political power. Between the years 800 and 907, this area suffered prolonged droughts and devastating floods, the traces of which were reconstructed using an ingenious method.

To reconstruct past hydrological conditions, scientists relied on tree ring analysis. These annual growth rings are wider in wet years and narrower during dry periods. Data collected in the Yellow River basin allowed for the modeling of water flows and their availability for irrigation.

The evolution of the climate had direct repercussions on agriculture. Water shortages compromised harvests, especially with the gradual adoption of wheat and rice, cereals more sensitive to drought than traditional millet. This change increased the risks of crop failures and famines.

Faced with these food difficulties, populations were weakened, particularly the soldiers tasked with defending the borders. The research indicates that a large number of them then migrated south in search of better living conditions, which helped to destabilize the ruling power.

It is important to keep in mind that these results are approximations, as multiple factors come into play in the decline of an empire. Nevertheless, they highlight how environmental disruptions can weaken a society.

Tree rings, natural archives

Trees preserve a memory of past environmental conditions in their wood. Each year, they form a new ring, whose width depends directly on the climate. When rainfall is abundant, growth is rapid and the ring is wide. Conversely, during periods of drought, growth slows, leaving a narrower ring.

This method, called dendrochronology, allows us to go back several centuries. By examining ancient trees, scientists can reconstruct annual climate variations with great accuracy. The data is often cross-referenced with other natural archives to refine the models.

In the case of medieval China, tree rings from the Yellow River basin were used to estimate historical water flows. This information helped to understand how water resources fluctuated, influencing agriculture and the life of the populations.

Dendrochronology is thus a valuable tool for historians and climatologists. It allows for a better understanding of the interactions between climate and human societies throughout the ages, without relying solely on ancient texts.