Central Asia is located in the hinterland of the Eurasian continent, far from the ocean, and with drastic temperature changes, it has become one of the significant arid regions. Studying the hydrological and climatic changes since the geological history of Central Asia is particularly important, as it helps to understand the historical hydrological changes in Central Asia and provides a reference for predicting future precipitation trends in this region in the context of global warming. There have been many achievements in the reconstruction of humidity in Central Asia during the Holocene, and most of the hydrological and climatic records in Central Asia during the Holocene come from the eastern region of Xinjiang, China. The current precipitation in this region is concentrated in the summer half year, in contrast to the current winter half year precipitation pattern in western Central Asia. This has raised questions such as whether the hydrological and climate changes in the eastern and western regions of Central Asia, which have different seasonal patterns of precipitation, have been synchronized in the past, when and what kind of climate crises have Central Asia experienced, and their impact on social development.

Tan Liangcheng, the research team of extreme climate events and impacts of the Institute of Earth Environment, Chinese Academy of Sciences, and An Zhisheng, an academician of the CAS Member, together with scientific researchers at home and abroad, studied stalagmite samples collected from the Fergana Basin, Kyrgyzstan. This study integrated stalagmite oxygen, carbon isotopes, and Sr/Ca ratio indicators to construct high-precision dating and high-resolution hydroclimatic records of the western Central Asia region over the past 7800 years. Research shows that since the Middle Holocene, the western region of Central Asia has shown a gradual drying trend. This is consistent with the decrease in the number of local archaeological sites, as well as the decrease in precipitation indicated by geological and biological records such as stalagmites, lakes, and peat in the West and East Mediterranean regions dominated by winter precipitation. The records of loess, peat, and spore pollen located in the eastern part of Central Asia indicate a long-term trend of humidification during the Holocene, which is in contrast to the long-term drought in the western region. Further research has found that this difference is attributed to the different responses of winter and summer westerly jets in Central Asia to seasonal solar radiation. Since the Holocene, the summer sunshine in the northern hemisphere has decreased, and the summer westerly jet has strengthened and moved southward over Central Asia, leading to an increase in precipitation in the eastern region of Central Asia, which is mainly characterized by summer half year precipitation. On the contrary, in the western region of Central Asia, which is dominated by winter precipitation, due to the increase in winter sunshine in the northern hemisphere, the winter westerly jet moves northward and is accompanied by an increase in temperature, reducing Mediterranean storm activity and reducing water vapor transport to Central Asia, resulting in a decrease in winter precipitation and snow cover in the region. This suggests that in the future, with the continuous increase of winter solar radiation and global warming, the region from western Central Asia to West Asia may face the threat of continuous reduction in precipitation.

Furthermore, the study found through analysis of wet and dry records in western Central Asia that the 1400 year, 50-70 year, and 20-30 year cycles in the region may be related to climate fluctuations in the North Atlantic, indicating a connection between climate change in Central Asia and the global climate system. Among them, drought events on the century to decade scale have had an impact on the history, society, and even cross-cultural exchanges in the region. For example, the super drought event that occurred 5180-5820 years ago hindered the expansion of Central Asian culture and delayed cultural exchanges along the prehistoric Silk Road oasis corridor. After the major drought, the gradual recovery of precipitation promoted the prosperity of the Bronze Age civilization in Central Asia, namely the rise of the Bactrian Margiana civilization, and led to the migration of nomadic peoples from the Eurasian grasslands to the south. In addition, the prosperity of the Persian Empire spanning across the three continents of Asia, Africa, and Europe coincided with the humid climate period in this region.

This work provides a detailed hydrological and climatic background of the western region of Central Asia over the past 7800 years, which is of positive significance for exploring the cultural changes in the region since the Neolithic Age. Meanwhile, the study reveals different precipitation trends driven by orbits between the eastern and western regions of Central Asia, which can help improve prediction models for future climate change in this ecologically fragile region.

Recently, the relevant research results have been published in the Journal of the National Academy of Sciences (PNAS) in the United States. The research work was supported by the National Natural Science Foundation of China and the Chinese Academy of Sciences strategic leading science and technology project.