| 27 Apr 2026
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.
This study collected shrub tree-ring samples from 26 sites in a region influenced by both the westerlies and East Asian summer monsoon (EASM). By establishing chronologies and analyzing the relationship with climatic factors, the study found that water is the primary limiting factor affecting shrub growth. It is found that shrub growth shows no clear relationship with the westerlies and EASM on an interannual scale, characterizing by a positive correlation with westerlies and a negative correlation with the EASM on a decadal scale. I recommend a revision.
Major comments:
Lines 263 and 274: Figure 5 and Table 1 show a strong correlation between the tree-ring chronology and the westerlies and EASM. However, this correlation is based on time-series data obtained from 11-year moving average. This may introduce spurious correlations, creating the illusion of strong correlation. As shown in Figure 4, the correlations are not strong at the interannual scale. And the differences in decadal trends, shown in Figure 5, are quite pronounced. These increase the likelihood of spurious correlation.
Line 402: The authors use the foehn effect to explain the negative impact of the EASM on tree growth. However, EASM has a dual role, bringing both moisture and the foehn effect. Analyzing the impact of EASM on drought in the study area would help strengthen the conclusions.
The authors aim to elucidate the interaction between the westerlies and EASM on the climate of the study area. But, shrub growth under different westerlies and the EASM (Figure 5) does not adequately answer the scientific questions. The authors have identified that shrub growth in this region is influenced by moisture conditions. So, I suggest establishing structural equation models (or other functions) comprising factors such as westerlies, EASM, climate factors and chronologies. By comparing the direct and indirect effects of the westerlies and EASM on shrub growth, you can demonstrate the direction and intensity of their effects.
Text and figures require correction. Such as the punctuation in Line 160, the font size in the figures and the order of sub-figures in Figure 7.