Relationship between the rise and fall of Loulan ancient city and centennial-scale climate events and cycles

The discovery of Loulan ancient city (LA) in the early 20th century has important significance for understanding the history of Western regions and the Silk Road civilization. The current academic community still has disputes on whether LA was the capital of Loulan Kingdom, the time of its rise, peak and decline, and the process, rate and driving mechanism of human activity change. This study uses the radio carbon dates (¹⁴C) database of LA to reconstruct the history of the rise and fall of human activity, and finds that LA experienced more than ∼500 years from its rise to its peak and then to its decline: 1) the city rose rapidly, and the population increased rapidly from ∼A.D. 0 to 230; 2) the city was prosperous and flourishing, and the intensity of human activity reached its peak from ∼A.D. 160 to 340, especially in ∼A.D. 230, when the population reached its peak; 3) the city accelerated its decline, and the intensity of human activity decreased significantly, and the population shrank rapidly from ∼A.D. 230 to 500; 4) LA was completely abandoned after ∼A.D. 560. The results of the ¹⁴C dating database do not support that LA was the early capital of the Loulan Kingdom. By comparing the human activity record of LA with the existing high-resolution palaeoclimate records in the surrounding mountainous areas of the Tarim Basin and South Asia, it is found that the superposition of centennial-scale westerly circulation strength events and the ∼500-year cycle of the Indian monsoon jointly controlled the precipitation and meltwater (snow) supply of the mountains in the Tarim Basin, affecting the changes of surface runoff and oasis area in the basin, which is one of the important factors causing the rise and fall of LA.