the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Aug 2025
Disentangling controls of multi-scale variability in Precipitation Stable Isotopes at Yadong and Ali on the Tibetan Plateau
Abstract. Understanding precipitation stable isotope variability over the Tibetan Plateau (TP) is essential for identifying moisture sources and assessing climatic responses. However, drivers of daily and synoptic-scale variability beyond the westerlies and Indian Summer Monsoon (ISM) remain poorly constrained in the southern and western TP. Using event-based precipitation isotope data (δ¹⁸O and δD) from Yadong and Ali (May 2021–September 2023), we investigate multi-scale variability drivers. Both sites exhibit nearly identical δ¹⁸O and δD magnitudes during the monsoon (June–September), while the westerly-dominated season (November–February) shows maximum differences of 12.2 ‰ in δ¹⁸O and 118.8 ‰ in δD. Meteorological controls vary seasonally: amount effects dominate during the monsoon (R = −0.28 to −0.32, p < 0.05), while temperature effects prevail in the westerly season (R = 0.51–0.79, p < 0.001). ISM dominates during isotopic convergence, while westerlies drive divergence via distinct transport pathways. Local Meteoric Water Line analysis indicates stronger moisture recycling and sub-cloud evaporation variability at Yadong. On synoptic scales, simultaneous precipitation events reflect coherent ISM influence. Interannual variability is significantly modulated by ENSO, with δ¹⁸O enrichment of 2.8–5.1 ‰ from La Niña to El Niño. During El Niño, weakened Walker circulation reduces ISM transport and enhances local evapotranspiration. These results offer new constraints on seasonal moisture source transitions and reveal ENSO sensitivity exceeding previous estimates, advancing understanding of atmospheric moisture transport and regional climate sensitivity over the TP.
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Status: open (until 31 Oct 2025)
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CC1: 'Comment on egusphere-2025-3567', Yuankun Zhang, 08 Oct 2025
reply
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CC2: 'Reply on CC1', Ke Li, 30 Oct 2025
reply
Based on multi-year precipitation isotope observation data from Yadong and Ngari, combined with backward trajectories, local meteorological elements, and reanalysis data, this study systematically reveals the variation characteristics and controlling mechanisms of stable isotopes in precipitation on the Tibetan Plateau across daily to interannual scales. The research clearly delineates the differences in moisture contributions between the Indian Summer Monsoon and the westerly circulation across seasons and quantitatively assesses the significant impact of ENSO on precipitation isotope composition by regulating moisture transport pathways. This work holds important value for deepening the understanding of the plateau's hydrological cycle processes and interpreting paleoclimate records.
After careful reading, the following points are provided for the author's consideration:
First, the interpretation of the isotope data is generally consistent throughout the paper. However, the explanation of isotopic fractionation mechanisms in different seasons using the Local Meteoric Water Line (LMWL) and Rayleigh fractionation curves is somewhat generalized. For instance, the data points for the Yadong monsoon season are highly scattered, distributed both below the Rayleigh curve and above the mixing line. It is worth further discussion whether this can be attributed to the combined effects of mixing and below-cloud secondary evaporation. In particular, the Ali region exhibits high slopes and high intercepts but does not fall above the Rayleigh curve, which appears inconsistent with the interpretation for Yadong.
Reply: Thank you for your suggestion. We will further discuss the combined effects of mixing and sub-cloud evaporation on the Yadong monsoon period according to the reader's suggestions, and add the discussion that the data points distributed above the mixing line are attributed to the influence of local surface evaporation.
Second, some figures could be further optimized to improve readability: In Figure 2, the borders of some subplots are misaligned, and it is suggested to standardize the formatting. In Figure 3, symbols for different seasons overlap significantly, and it is recommended to present them in separate panels or use more distinguishable legends.
Reply: Thank you for your suggestion. Following the reader's comments, we will standardize the formatting in Figure 2, and use more distinguishable legends in Figure 3 to improve readability .
Third, the content explained in Figure 4 (backward trajectories), Figure 5, and Figure 6 (moisture flux) is consistent with the isotope interpretation discussed earlier. However, there is some overlap in their content. It is advisable to more clearly distinguish their respective conclusions in the textual explanation or consider integrating the images to enhance the conciseness of the information.
Reply: Thank you for your suggestion. We will consider refining the content explained in Figure 4, Figure 5, and Figure 6 according to the suggestions.
Overall, this study is supported by solid data and comprehensive methodology, providing important observational constraints for regional moisture source tracing and isotope research.
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AC1: 'Reply on CC1', Aibin Zhao, 30 Oct 2025
reply
We thank all the reviewers for their constructive comments. We have made our best to address all the comments.
CC1: 'Comment on egusphere-2025-3567', Anonymous Referee #1,
Based on multi-year precipitation isotope observation data from Yadong and Ngari, combined with backward trajectories, local meteorological elements, and reanalysis data, this study systematically reveals the variation characteristics and controlling mechanisms of stable isotopes in precipitation on the Tibetan Plateau across daily to interannual scales. The research clearly delineates the differences in moisture contributions between the Indian Summer Monsoon and the westerly circulation across seasons and quantitatively assesses the significant impact of ENSO on precipitation isotope composition by regulating moisture transport pathways. This work holds important value for deepening the understanding of the plateau's hydrological cycle processes and interpreting paleoclimate records.
After careful reading, the following points are provided for the author's consideration:
First, the interpretation of the isotope data is generally consistent throughout the paper. However, the explanation of isotopic fractionation mechanisms in different seasons using the Local Meteoric Water Line (LMWL) and Rayleigh fractionation curves is somewhat generalized. For instance, the data points for the Yadong monsoon season are highly scattered, distributed both below the Rayleigh curve and above the mixing line. It is worth further discussion whether this can be attributed to the combined effects of mixing and below-cloud secondary evaporation. In particular, the Ali region exhibits high slopes and high intercepts but does not fall above the Rayleigh curve, which appears inconsistent with the interpretation for Yadong.
Reply: Thank you for your suggestion. We will further discuss the combined effects of mixing and sub-cloud evaporation on the Yadong monsoon period according to the reader's suggestions, and add the discussion that the data points distributed above the mixing line are attributed to the influence of local surface evaporation.
Second, some figures could be further optimized to improve readability: In Figure 2, the borders of some subplots are misaligned, and it is suggested to standardize the formatting. In Figure 3, symbols for different seasons overlap significantly, and it is recommended to present them in separate panels or use more distinguishable legends.
Reply: Thank you for your suggestion. Following the reader's comments, we will standardize the formatting in Figure 2, and use more distinguishable legends in Figure 3 to improve readability .
Third, the content explained in Figure 4 (backward trajectories), Figure 5, and Figure 6 (moisture flux) is consistent with the isotope interpretation discussed earlier. However, there is some overlap in their content. It is advisable to more clearly distinguish their respective conclusions in the textual explanation or consider integrating the images to enhance the conciseness of the information.
Reply: Thank you for your suggestion. We will consider refining the content explained in Figure 4, Figure 5, and Figure 6 according to the suggestions.
Overall, this study is supported by solid data and comprehensive methodology, providing important observational constraints for regional moisture source tracing and isotope research.
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CC2: 'Reply on CC1', Ke Li, 30 Oct 2025
reply
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RC1: 'Comment on egusphere-2025-3567', Anonymous Referee #1, 30 Oct 2025
reply
The study of precipitation stable isotopes is of great significance for tracing the water vapor source and studying the water cycle, and it is also of great importance for reconstructing past climatic and environmental changes. This paper investigated the characteristics and mechanisms of multi-scale variability in precipitation stable isotopes in the southern and western Tibetan Plateau. It is worth noting that this paper demonstrates that Indian Summer Monsoon (ISM) circulation homogenizes isotopic signatures across the southern and western Tibetan Plateau, while westerly dominance amplifies regional differences through distinct moisture pathways, and ENSO significantly influences the interannual variability of precipitation stable isotopes in the study area. However, the paper has some issues that require further improvement and clarification.
General comments:
- About positive values of δ18O and δD in precipitation at the study sites. Figure 2 shows that there are a large number of positive values of δ18O and δD at the two study sites, especially at Yadong. It is necessary to analyze and explain the reasons for the occurrence of these positive values and their indicative significance.
- Regarding the selection of altitudes/heights at which the air parcels reach the study sites in backward trajectory analysis. It was pointed out in lines 200-204 that “to assess the influence of moisture sources on precipitation stable isotopes, to calculate 120 h backward trajectories for air masses arriving 200 m above ground level at Yadong and Ali stations.” Another thing is that the heights used for calculating water vapor flux are from 500 hPa to 200 hPa in this study. These analyses are all intended to explain the sources and paths of water vapor, but there is inconsistency in the selection of the levels. Since this study focuses on the stable isotopes of precipitation, why not choose the condensation levels instead of 200 m above ground level to calculate the trajectory of the air parcels reaching the study sites? If the condensation levels or 500 hPa or other heights are chosen, will the backward trajectories be significantly different from the current ones? These should be analyzed and explained.
Specific comments:
- The variation of precipitation throughout the year at Yadong is bimodal, with two peaks in April and October. What is the impact of this pattern of precipitation variation on precipitation stable isotopes? Or what characteristics of precipitation isotopes can indicate the peak precipitation information? If there is currently sufficient data available for the issues, please discuss and explain them.
- Lines 219-220, where g is gravitational acceleration, while Ps and Pt are surface pressure and top pressure, respectively. The expression of Pt is inaccurate.
- In Figure 2(f), (g), (h), (i), (j), especially in (j), the units of their vertical coordinates should be displayed.
- According to the definition of seasonal division in lines 232-236, the “late monsoon (October)” should be the “post-monsoon”? And pay attention to the expression of “late monsoon” in the following text.
- Line 434, “ISM dominated the moisture transport during pre-monsoon of 2021”. In this sentence, the first part is about the monsoon (ISM), but the second part mentions “during pre-monsoon”. It seems that the logic or expression is not accurate literally. Similar expressions can also be found in other parts of the text. Please make corrections and/or clarifications. If possible, the seasons can be divided based on the specific dates of the onset and withdrawal of the Indian monsoon each year during the study period in this paper. This seasonal division might be more meaningful for the study of precipitation stable isotopes.
Citation: https://doi.org/10.5194/egusphere-2025-3567-RC1
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Based on multi-year precipitation isotope observation data from Yadong and Ngari, combined with backward trajectories, local meteorological elements, and reanalysis data, this study systematically reveals the variation characteristics and controlling mechanisms of stable isotopes in precipitation on the Tibetan Plateau across daily to interannual scales. The research clearly delineates the differences in moisture contributions between the Indian Summer Monsoon and the westerly circulation across seasons and quantitatively assesses the significant impact of ENSO on precipitation isotope composition by regulating moisture transport pathways. This work holds important value for deepening the understanding of the plateau's hydrological cycle processes and interpreting paleoclimate records.
After careful reading, the following points are provided for the author's consideration:
First, the interpretation of the isotope data is generally consistent throughout the paper. However, the explanation of isotopic fractionation mechanisms in different seasons using the Local Meteoric Water Line (LMWL) and Rayleigh fractionation curves is somewhat generalized. For instance, the data points for the Yadong monsoon season are highly scattered, distributed both below the Rayleigh curve and above the mixing line. It is worth further discussion whether this can be attributed to the combined effects of mixing and below-cloud secondary evaporation. In particular, the Ali region exhibits high slopes and high intercepts but does not fall above the Rayleigh curve, which appears inconsistent with the interpretation for Yadong.
Second, some figures could be further optimized to improve readability: In Figure 2, the borders of some subplots are misaligned, and it is suggested to standardize the formatting. In Figure 3, symbols for different seasons overlap significantly, and it is recommended to present them in separate panels or use more distinguishable legends.
Third, the content explained in Figure 4 (backward trajectories), Figure 5, and Figure 6 (moisture flux) is consistent with the isotope interpretation discussed earlier. However, there is some overlap in their content. It is advisable to more clearly distinguish their respective conclusions in the textual explanation or consider integrating the images to enhance the conciseness of the information.
Overall, this study is supported by solid data and comprehensive methodology, providing important observational constraints for regional moisture source tracing and isotope research.