Spatial and Temporal Variations in Rainfall Seasonality and Underlying Climatic Causes in the Eastern China Monsoon Region

Comments 1: Abstract: Could have been written better. Also include and elaborate quantitative results and conclusion in abstract.

Response 1: Thank you bring this to our attention. We modified the Abstract section in the revised manuscript, please see Page 1. The Abstract is also attached as follows:

The regularity of rainfall seasonality is very important for vegetation growth, livelihood of population, agricultural production, and ecosystem sustainability. The changes in precipitation and its extremes have been widely reported, however, the spatial and temporal variations of rainfall seasonality and underlying mechanisms are less understood. Here, we analyzed the changes in rainfall seasonality and possible teleconnection mechanisms in eastern China monsoon region during 1981–2022, with a special focus on El Niño-Southern Oscillation (ENSO), El Niño Modoki (ENSO_M), and Indian Ocean Dipole (IOD). Our results show that due to the changes in rainfall concentration, rainfall magnitude, or both, rainfall seasonality enhances in northern China (NC, 0.15×10^-3 yr^-1) and central China (CC, 0.07×10^-3 yr^-1) monsoon regions, and weakens in northeastern China (NEC, -0.08×10^-3 yr^-1) and southern China (SC, -0.15×10^-3 yr^-1) monsoon regions during recent decades. The large-scale circulation and SST anomalies induced by cold or warm phases of IOD, ENSO_M, and (or) ENSO can well explain the enhanced seasonality in NC and CC monsoon regions and weakened seasonality in NEC and SC monsoon regions. The wavelet coherence analysis further shows that the dominated climatic factors for rainfall seasonality changes are different in CC, NC, SC, and NEC monsoon regions, and rainfall seasonality are also affected by the coupling of IOD, ENSO_M, and ENSO. Our results highlight that IOD, ENSO_M, and ENSO are important climatic causes for rainfall seasonality changes in eastern China monsoon region.

Comments 2: Introduction: The authors described objectives very general, it should be specific which parameters will be used for rainfall seasonality.

Response 2: Thank you for this valuable suggestion. We revised the text in the resubmitted manuscript, please see Page 3, lines 102-105. The corresponding text can be attached as follows:

Therefore, the objectives of this study are to analyze the spatial and temporal variations of rainfall seasonality based on the novel seasonality indices proposed by Feng, et al. [1] during 1981–2022, and to investigate possible teleconnection mechanisms in eastern China monsoon region, with a special focus on ENSO, ENSO_M, and IOD.

Comments 3: Study Area: The scale bar should not be on top of study area boundary, please corrected Figure 1 map.

Response 3: Thank you for bringing this to our attention. We revised Figure 1. (See page 3, line 126). Figure 1 is also attached as follows:

Figure 1. Sketch of the study area

Comments 4: Methods: The authors should be briefly explain about Sen Slope and Modified Mann-Kendall (MMK), why these methods are significant for this study.

Response 4: Thank you for your comment. We modified the section 2.3.2 in the revised manuscript, please see pages 4-5, lines 161-166. The text is attached as follows:

The modified Mann-Kendall (MMK) method can avoid interference from outliers and remove autocorrelated components in time series [67]. Sen’s slope [68] and Mann–Kendall methods are usually applied together and have been widely utilized to many cli-mate-analysis studies [69,70,71,72]. Therefore, Sen’s slope and MMK were used to analyze the interannual trend of rainfall seasonality in eastern China monsoon region. The trend significance was set at the 0.05 level [73].

Comments 5: Results and Discussion: In Figure 2, the authors should specify units of rainfall magnitude in legend.

Response 5: Thank you for bringing this to our attention. We added units of rainfall magnitude in legend, please see Page 6, Figure 3. This Figure is also attached as follows:

Figure 3 The climatology of monthly rainfall (a) and seasonality indices (b-d) in eastern China monsoon region during 1981 to 2022.

Comments 6: There are too many figures in manuscript, the authors may reduce number of figures or put some figures in supplementary materials.

Response 6: Thank you for your suggestion. Following your suggestion, we put some figures in supplementary materials.

Comments 7: The authors should extend discussion section by citing previous work in study area. Authors have combined Discussion with Conclusion which is not a usual practice but could be acceptable. The discussion section can be written separately.

Response 7: Thank you for your suggestion. We carefully revised the Results and Discussion sections, and the Results and Discussion section were written separately. Please see the Results and Discussion sections in the resubmitted manuscript.

Point-by-point response to Comments and Suggestions for Authors

Comments 1: Define and clarify the use of EMI, Nino 3.4, and DMI which appear numerous times in this paper. On line 132 they are defined as "global climate indeces". But on lines 410-415 EMI and DMI "are key driving factors". Indeces are driving factors? Clarify by making better reference in this regard to ENSO, ENSO_M, I and IOD.

Response 1: Thank you for your comments. In this work, we analyzed the changes in rainfall seasonality and possible teleconnection mechanisms in eastern China monsoon region during 1981–2022, with a special focus on ENSO, ENSO_M, and IOD. Nino 3.4, EMI, and DMI were used to indicate ENSO, ENSO_M, and IOD, respectively. In the resubmitted manuscript, we revised as ENSO, ENSO_M, and IOD.

Comments 2: Line 191-193: references to black line and area within are out of place here. Move to section of paper showing plot.

Response 2: Thank you for your comments. We moved the references of the black line and area to Result section, please see Page 10, Lines 311-316.

Response to Comments on the Quality of English Language

Point 1: This paper is generally well written, but requires numerous grammatical changes, including choice of words, and sentence structure. Recommendation: Have an individual proficient in the English language thoroughly review this paper and make corrections.

Response 1: Thank you for your suggestions. The English language of the revised manuscript was polished by AJE Company. We further carefully checked and revised formatting issues and grammar errors in the revised manuscript.

Comments 1: The Abstract should present numerical results and highlight the main findings.

Response 1: Thank you for bringing this to our attention. We modified the Abstract section in the revised manuscript, please see Page 1. The Abstract is also attached as follows:

The regularity of rainfall seasonality is very important for vegetation growth, livelihood of population, agricultural production, and ecosystem sustainability. The changes in precipitation and its extremes have been widely reported, however, the spatial and temporal variations of rainfall seasonality and underlying mechanisms are less understood. Here, we analyzed the changes in rainfall seasonality and possible teleconnection mechanisms in eastern China monsoon region during 1981–2022, with a special focus on El Niño-Southern Oscillation (ENSO), El Niño Modoki (ENSO_M), and Indian Ocean Dipole (IOD). Our results show that due to the changes in rainfall concentration, rainfall magnitude, or both, rainfall seasonality enhances in northern China (NC, 0.15×10^-3 yr^-1) and central China (CC, 0.07×10^-3 yr^-1) monsoon regions, and weakens in northeastern China (NEC, -0.08×10^-3 yr^-1) and southern China (SC, -0.15×10^-3 yr^-1) monsoon regions during recent decades. The large-scale circulation and SST anomalies induced by cold or warm phases of IOD, ENSO_M, and (or) ENSO can well explain the enhanced seasonality in NC and CC monsoon regions and weakened seasonality in NEC and SC monsoon regions. The wavelet coherence analysis further shows that the dominated climatic factors for rainfall seasonality changes are different in CC, NC, SC, and NEC monsoon regions, and rainfall seasonality are also affected by the coupling of IOD, ENSO_M, and ENSO. Our results highlight that IOD, ENSO_M, and ENSO are important climatic causes for rainfall seasonality changes in eastern China monsoon region.

Comments 2: The final section of the abstract is written in a very general way and does not seem to address the following: "provide valuable information for sustainable economic and social development".

Response 2: Thank you for your suggestion. We modified the Abstract section in the revised manuscript, please see Page 1, lines 28-29.

Comments 3: In the introduction and line 62, 6 sources are provided to support a sentence "on precipitation variability in eastern China monsoon region [24-30]. " This style should be changed in writing the text and a specific type of citations should be used.

Response 3: Thank you for your comment. We checked the Introduction section and used the specific type of citation in the revised manuscript, please see the Introduction section.

Comments 4: In the introduction section, it is necessary to refer to the indicators/approaches used in calculating "Seasonality" and to discuss related research in this field.

Response 4: Thank you for your comment. Following your suggestion, we modified the Introduction section, and also discuss related research in the field of seasonality indices, please see Pages 1-2, Lines 43-51. The text is also attached as follows:

Rainfall seasonality is closely related to rainfall magnitude and rainfall concentration [14,15,16]. Traditionally, the characteristics of rainfall seasonality were quantified by relative rainfall intensity, rainfall in dry and wet seasons, and the timing of 25–75% of total rainfall [17]. However, traditional seasonality indices are difficult to consider rainfall differences and its temporal distribution [18]. To better understand the changing patterns of rainfall seasonality, Feng, et al. [1] proposed several novel seasonality indices, including seasonality index, rainfall magnitude, and rainfall concentration, based on the information theory to quantitively describe the aspects of rainfall seasonality in a unified framework.

Comments 5: It is necessary to include literature review in the introduction in one paragraph and describe several previous studies, and then provide a summary of the research history and highlight the importance of the present study.

Response 5: Thank you for your comment. In the reviewed manuscript, we describe several previous studies, and highlight the importance of our study in the section of introduction, please see page 2, lines 51-59. The text is also attached as follows:

Many previous researches have investigated rainfall seasonality changes based on seasonality indices proposed by Feng, et al. [1], and found that rainfall seasonality has changed significantly in many parts of world [1,12]. For example, the increases in the in-terannual variability of seasonality over many parts of the dry tropics [1] and Southeast China [19]. Significant decreasing trends in rainfall seasonality were also observed over the Indo-Gangetic plains, and parts of central India and Western Ghats [18]. Although the changes in rainfall seasonality have been widely reported in much of the world, the possible mechanisms behind the changes in rainfall seasonality at the reginal scale, such as in eastern China monsoon region, are still largely unclear.

Comments 6: The introduction section does not contain any information about the novelty.

Response 6: Thank you for your comments. We modified introduction section in the reviewed manuscript, please see introduction section, page 3, lines 100-107. The corresponding text is attached as follows:

However, the spatial and temporal variations of rainfall seasonality and especially underlying climatic causes are still less understood. Therefore, the objectives of this study are to analyze the spatial and temporal variations of rainfall seasonality based on the novel seasonality indices proposed by Feng, et al. [1] during 1981–2022, and to investigate possible teleconnection mechanisms in eastern China monsoon region, with a special focus on ENSO, ENSO_M, and IOD. Our study also provides a new perspective on analyzing the individual and coupled influences of global climate events on rainfall seasonality changes at regional scales.

Comments 7: In the "Method" section, it is better to show the steps of the work with a flowchart.

Response 7: Thank you for this valuable suggestion. In the revised manuscript, we added the steps of the work with a flowchart in Method section, please see Page 4. The Figure is also attached as follows:

Figure 2. The technical flowchart of research methods.

Comments 8: Mention in which software/programming platform the analyses of each part were performed in methodology section.

Response 8: Thank you for your comments. In this work, all of data processing and analysis were performed using MATLAB software, please see the section of methods, page 4, lines 145-146.

Comments 9: In the results and Figure 8.c, the correlation values are greater than 1, revision is required.

Response 9: Thank you for this valuable suggestion. We modified the partial correlations map in the revised manuscript, please see Page 10. In this Figure, the correlation values are less than 1 in all of grid points. The Figure is also attached as follows:

Figure 7 Spatial distributions of partial correlations between DMI, Niño3.4, and EMI and seasonality index in eastern China monsoon region. d presents the spatial average correlation coefficients in different eastern China monsoon regions.

Comments 10: It is difficult to debunk the interpretation of the figures, the following procedure should be followed: “first, refer to the figure, then present the figure, and finally, provide explanations and interpretations after the figure.”

Response 10: Thank you bring this to our attention. Following your suggestion, we modified the section of results, and followed the following procedure: “first, refer to the figure, then present the figure, and finally, provide explanations and interpretations after the figure.” Please see the Results section.

Comments 11: Make practical suggestions for application of the results in practical purposes based on the results.

Response 11: Thank you for your comments. Based on our results, we made practical suggestions for application of the results of practical purposes in the Conclusion section, please see page 14, lines 433-436.

Comments 12: Mentioning the research limitations and the uncertainty in the results would help.

Response 12: Thank you for this valuable suggestion. In the revised manuscript, we mentioned the research limitations in the Discussion section, please see pages 13-14, lines 373-416.

Comments 13: Propose directions for future research based on the findings.

Response 13: Thank you for your comments. We added the directions for future research in the Discussion section, please see pages 13-14, lines 373-416.