The Qin and Western Han dynasties (221 BCE to 24 CE) represent an era of societal prosperity in China. However, due to a lack of high-resolution paleoclimate records it is still unclear whether the agricultural boost documented for this period was associated with more favorable climatic conditions. Here, multiparameter analysis of annually resolved tree-ring records and process-based physiological modeling provide evidence of stable and consistently humid climatic conditions during 270 to 77 BCE in northern China. Precipitation in the Asian summer monsoon region during the Qin-Western Han Dynasties was ~18 to 34% higher compared to present-day conditions. In shifting agricultural and pastoral boundaries ~60 to 100 km northwestward, possibility up to 200 km at times, persistently wetter conditions arguably increased food production, contributing to the socioeconomic prosperity around 2,200 y ago. A gradual wetting trend in the western part of arid northwestern China since the 1980s resembles the historical climate analogue, suggesting that similar benefits for regional environmental and agricultural systems may reoccur under current climate change, at least in the near term.

Bolin Centre for Climate Research Stockholm University Stockholm 106 91 Sweden

Centre for Ecological and Evolutionary Synthesis Department of Biosciences University of Oslo Oslo 0316 Norway

Climatic Research Unit School of Environmental Sciences University of East Anglia Norwich NR4 7TJ United Kingdom

Department of Environmental and Biodiversity University of Salzburg Salzburg 5020 Austria

Department of Geography Faculty of Science Masaryk University Brno 611 37 Czech Republic

Department of Geography Johannes Gutenberg University Mainz 55099 Germany

Department of Geography Justus Liebig University of Giessen Giessen 35930 Germany

Department of Geography University of Cambridge Cambridge CB2 3EN United Kingdom

Department of History Stockholm University Stockholm 106 91 Sweden

Global Change Research Institute Czech Academy of Sciences Brno 603 00 Czech Republic

Institute of Geography Friedrich Alexander University Erlangen Nürnberg Erlangen 91058 Germany

Key Laboratory of Ecological Safety and Sustainable Development in Arid Lands Northwest Institute of Eco Environment and Resources Chinese Academy of Sciences Lanzhou 730000 China

Mathematical Methods and Information Technology Department Siberian Federal University Krasnoyarsk 660075 Russia

School of Atmospheric Sciences Nanjing University Nanjing 210023 China

School of Geography and Ocean Science Nanjing University Nanjing 210023 China

Swedish Collegium for Advanced Study Uppsala 752 38 Sweden

Swiss Federal Research Institute for Forest Snow and Landscape Research Birmensdorf 8903 Switzerland

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Persistent humid climate favored the Qin and Western Han Dynasties in China around 2,200 y ago