Manuscript title: Drought reconstruction since 1796 CE based on tree-ring widths in the Upper Heilongjiang (Amur) River Basin in Northeast Asia, and its linkage to Pacific Ocean climate variability

This manuscript presented a reconstruction of the May-July scPDSI sequence since 1796 from tree rings in the Upper Heilongjiang (Amur) River Basin. The study area is located in the climate-sensitive arid-semi-arid border region of China, which is also the location of cross-border rivers. The reconstruction is reliable and capture acceptable variance of the instrumental precipitation. The authors seem to want to link global climate change to regional extreme droughts. However, some of the analyses are preliminary and not perfect. In general, the  presented results are reasonable, but the following concerns should be addressed before it can be reconsidered for publication.

• As the reconstructions in the manuscript reflect only a relatively small area of the upper Heilongjiang (Amur) River basin, in the citation section I would like the authors to indicate what the implications of your study are for other areas, please improve on this point.
• In the Methods or the supplemental, it would be good to know more about how the tree-ring data were standardized and truncated to control for signal strength. Were short series removed?
• In section 2.3, it is necessary to clarify how the correlation coefficient is calculated, as the widely used Pearson method should check whether the data set shows a normal distribution. In this case, Spearman's rank test is often used as an alternative method of calculation.
• “2.4 Land-atmosphere water balance”: This section is overloaded with descriptions and explanations of calculation methods, which should not be the focus of the methods section.
• In the discussion section, the manuscript lacks a comparison with the results of reconstructions in other neighbouring areas.
• The drought index used in this manuscript is the self-calibrating Palmer Drought Severity Index (scPDSI). However, the various drought indices do not have exactly the same focus. Will the reconstructed precipitation have a similar response pattern to other drought indices (e.g. SPEI)?
• The hydrological data used in this study is too far from the tree ring sampling sites. It also includes the input of other branch rivers, besides the human activities.
• Title of 4.1 is to discuss “Climate–tree ring growth relationships and temporal variations259

in regional drought”. “NEC is a major food-producing region in China, and thus it is of both regional and national importance to improve our understanding of the causes and patterns of drought events and to develop appropriate responses.” These sentences are not relevant to the topic of the section.

• The year should be expressed in a unified way, some with “CE” and some without “CE”.
• Line 59: “several studies based on tree-ring width have been conducted in Northeast Asia ”,What is the scientific problem in the current researches? Why did you carry out this study? Just to make a new reconstruction?
• Line 61-64: Please rephrase to make the description more clear.
• Line 71,125: Please correct the spacing between words
• Line 98: Show the specific meaning of “NEGC” and “MGET”.
• Line 98: The selection of the sampling sites is not sufficiently described. Lack of data about slope inclination and exposure.
• Line 102-105:“This region has a continental and monsoonal climate. Due to the incursion of high-latitude cold and dry air masses in winter and of warm and moist air masses from low-latitude areas in summer, the climate tends to alternate between cold and dry in winter and warm and humid in summer.” The description of the regional climate in the manuscript lacks an appropriate literature base.
• Line 123-130: Why the STD chronology was chosen among the three, the authors didn’t provide the necessary explanation of the characteristics of the other two categories.
• Line 144,148,212,225.250,253,272: Change “correlation” to “correlation coefficient”.
• Line 237-241: How did you get the 5 continuous wet periods and 4 continuous dry periods? What is the criterion. If you defined them by the cumulative anomaly curve , then the cumulative anomaly curve should be introduced before the periods.
• Line 281-300: The authors identify seven extreme drought years in the reconstruction results in the historical literature. However, the literature cited is sparse and does not provide sufficient proof of the reliability and authenticity of the results.
• Line 290 - 298:This sentence is tediously long, please revise it.
• Line 307: The impact of ENSO is shown on the SST anomaly composite graph for the extreme drought years of the SST. However, as seen in Figure 7, ENSO is the most obvious, but not the only one. Do SST variations in other regions also have an impact?
• Line 366-368: “These results suggest that water vapor transport processes play a key role in the development of drought in the Upper Heilongjiang (Amur) River Basin.”This sentence should be revised.
• Figure 1: The method of drawing Figure 1 should be given. Based on what data and software?
• Figure 3:What’s the thick black curve in each figure?
• Figure 4: High-frequency (1st order difference) comparison between the instrumental and reconstructed scPDSI should be given.
• Figure 4 (e): The curve in the diagram is not clear and I would like the author to change the colour to make it more legible.
• Figure 6: I would like the authors to add the results of the significance test to the correlation analysis.
• Figure 6: The small plots used as correlation between sequences in (a) and (b) are not very clear, and it is also recommended that some smoothing of the curves be added to this type of plot.
• Figure 6: For spatial correlation patterns, how about the result from the meteorological station (with CRU gridded precipitation, SST)?
• Figure 7,8,9: These 3 figures are missing units of data.

Summary: the authors have reconstructed the drought variability in the Upper Heilongjiang River Basin in Northeast Asia since 1796 based on tree-ring width and have explored its linkages with Pacific ocean-climate variability. Overall, the paper is well-written and well-organized, providing valuable insights into regional hydroclimate dynamics and mechanisms. However, there are some issues that need to be addressed.

I have one major concern:

The discussion section discusses large-scale climate driving factors that influence drought variability in the study area, including ENSO and the Silk Road teleconnection pattern, as well as the contributions of external moisture transport and local evaporation to precipitation in the atmospheric water cycle process. The discussion is insightful and plausible, but some arguments need more evidence and references to support them. For example, how do ENSO and the Silk Road teleconnection pattern affect atmospheric circulation and moisture transport over Northeast Asia? How reliable are the moisture flux data and calculations used in this study? How consistent are this study's findings with other studies in terms of climate mechanisms and impacts?

Other detailed comments are as follows:

1) In the title, the authors use “Northeast Asia”, which is inconsistent with the description in the introduction (e.g., Line 44, “northeast China”). It would be better to keep it consistent.

2) In lines 60-61, overall, the cited papers seem outdated (before 2018). I suggest citing more recent papers (since 2019) from nearby regions.

3) Line 82: What does “EU” stand for? It is unclear.

4) Line 91: Revise “To reconstruct” to “to reconstruct”.

5) Line 116: Revise “chest height” to “breast height”.

6) In lines 215-222: May-July scPDSI was found to be the dominant climatic signal in tree-ring widths. How about linkages of tree-ring width with SPEI at different scales? Maybe higher correlations could be detected.

7) Lines 234: Please specify what is meant by low-frequency. Which time domain? Inter-decadal?

8) Lines 262-263: Usually, the full Latin name is used for the first time, and abbreviations of genus names are shown for the rest. Therefore, please revise “Pinus sylvestris var. Mongolica” to “P. sylvestris var. Mongolica”.

9) Lines 591-593: In Table 1, the species name is “Pinus sylvestris”, different from “Pinus sylvestris var. Mongolica” in the body text. Please keep consistent.

10) Lines 642-650: Add the Amur River in (a) and (b), as shown in (c).