Interaction between the East Asian summer monsoon and Westerlies as shown by desert shrub-ring records from the Alxa Plateau, Northwest China

Abstract. The variations, driving mechanisms, and interactions between the mid-latitude westerlies and the Asian summer monsoon represent a critical focus in global change research. Extensive research has investigated climate change and its drivers across multiple timescales in the core regions of both westerlies Asia and monsoonal Asia. However, studies are far fewer in the arid inland deserts at the interactive margin of these two circulation systems, where precipitation restrict the distribution of trees. To address this gap, we developed 26 shrub-ring width chronologies of Zygophyllum xanthoxylum from four sub-regions of the Alxa Desert Plateau. Our analysis reveals that shrub radial growth is primarily limited by aridity during the growing season, driven by low precipitation. The four regional chronologies indicate substantial spatiotemporal heterogeneity in dry–wet variability. By integrating these records with indices of the westerlies and the East Asian summer monsoon (EASM), we demonstrate that hydroclimatic variations are primarily modulated by the interaction between these two circulations. The Alxa Plateau is predominantly influenced by the EASM, whose boundary can extend approximately 400 km northwestward to the Yabulai–Nurgong–Lang mountains line in the central plateau. This can cover the entire Tengger and Ulan Buh Deserts. Concurrently, the westerlies can advance eastward to affect the Helan Mountains. Thus, the Alxa Plateau constitutes a key transition zone and interaction arena between the westerlies and the EASM within China’s arid interior. At the same time, the foehn effect in the mountains around the Alxa Plateau also has a certain impact on atmospheric circulation. Climatic fluctuations in this region critically influence local vegetation dynamics and desertification processes, underscoring its importance for understanding past and future environmental change.