Precipitation variations in arid central Asia over past 2500 years: Possible effects of climate change on development of Silk Road civilization

The ecological environment of arid central Asia (ACA) is fragile and sensitive to long-term climate change. Recent palaeoclimatological studies have mainly focused on northwestern China, which is located on the eastern side of the region. Holocene palaeoclimate records from the western region of ACA are scarce, thus hindering the exploration of the relationship between climate change and Silk Road civilization. In this study, we conduct a pollen analysis of Lake Sasikul on the Pamir Plateau in Tajikistan and use pollen data to quantitatively reconstruct the precipitation history over the last 2500 years. The results show that herbaceous pollen is primarily represented by Artemisia and Amaranthaceae, thus suggesting the persistent dominance of grassland in the vicinity of Lake Sasikul. Amaranthaceae, which is the most drought-tolerant pollen type, shows the highest values during the Medieval Warm Period (MWP, 950-1300 CE). The values of Artemisia and cold-wet-adapted Picea pollen are higher during the Little Ice Age (LIA, 1550-1900 CE). The quantitative reconstruction shows that during the MWP, the mean annual precipitation is 120 mm, which is approximately 15% lower than the level of modern precipitation; meanwhile, during the LIA, the average annual precipitation is 160 mm (up to 210 mm), which is approximately 20% higher than the present value. We combine our results with regional temperature records and archaeological data to discuss the possible effects of climate change on the development of Silk Road civilization. The hydrothermal configuration may have altered water resources and thus affect human activities in ACA. From 580 to 900 CE, i.e. during the Sui and Tang Dynasties, ice and snow meltwater increased under warm climate, whereas the amount of precipitation was average. Additionally, human settlements intensified along with urbanization, and the Silk Road civilization was prosperous and well-developed. From 1270 to 1650 CE, i.e. during the Yuan and Ming Dynasties, under overall colder and drier conditions and due to insufficient freshwater input, the intensity of local human settlement weakened, and the Silk Road civilization declined. Therefore, owing to global warming and increasing precipitation, new development opportunities have emerged for the development of agriculture and social economy in ACA.