Ecological and societal effects of Central Asian streamflow variation over the past eight centuries

Understanding changes in water availability is critical for Central Asia; however, long streamflow reconstructions extending beyond the period of instrumental gauge measurements are largely missing. Here, we present a 785-year-long streamflow reconstruction from spruce tree rings from the Tien Shan Mountains. Although an absolute causal relationship can not be established, relatively high streamflow rates coincided roughly with the period of Mongol expansion from 1225 to 1260 CE and the rise of the Timurid Empire from 1361 to 1400 CE. Since overall wetter conditions were further found during the Zunghar Khanate period 1693-1705 CE, we argue that phases of streamflow surplus likely promoted oasis and grassland productivity, which was an important factor for the rise of inner Eurasian steppe empires. Moreover, we suggest that the streamflow variation might be critical for plague outbreaks in Central Asia, and propose several explanations for possible links with Europe's repeated Black Death pandemics. We demonstrate that 20th-century low streamflow is unprecedented in the past eight centuries and exacerbated the Aral Sea crisis, which is one of the most staggering ecological disasters of the twentieth century.

Automated summary

Understanding changes in water availability is crucial for Central Asia. However, long-term streamflow reconstructions are lacking. Based on a study of spruce tree rings from the Tien Shan Mountains, we found that periods of high streamflow coincided with the Mongol expansion and the rise of the Timurid Empire. Furthermore, we suggest that the streamflow variation may be linked to plague outbreaks in Central Asia and Europe's Black Death pandemics. We also discovered that low streamflow in the 20th century is unprecedented and worsened the Aral Sea crisis.