Water resource, circulation and infiltration, are essential for the regional ecosystem and society. This is an interesting work, focused on the changes of recharge threshold pre-post fire in a karst area of Australia. The authors monitoring the precipitation and discharge in cave, analyzed the data and compared the changes in recharge thresholds. The research design is simple and clear, and the data analysis is comprehensive and reasonable. The authors also pointed out some potential problems and imperfections. In general, I think this is an interesting and good manuscript. I can't pick on more and I recommend it to be published.

Review comments on the manuscript: Rainfall recharge thresholds decrease after an intense fire over a near-surface cave at Wombeyan, Australia by Song et al.

The manuscript presents an interesting study on the impact of (wild)fires on groundwater recharge. The authors compare post- and pre-fire rainfall recharge thresholds using time series from drip loggers situated in a karst cave in Australia. The topic is timely and relevant. The manuscript is well written and structured, and I recommend it for publication after minor revisions.

Main Comments

Most of the figures—especially Figure 1—are visually unappealing and difficult to interpret:

•    Figure 1a, 1b, and 1c are too small and blurry to discern the details referred to in the caption or main text - L204: “The decrease in rainfall recharge threshold is not observed immediately post-fire, when the land surface above the cave was covered with thick ash deposits (see Fig. 1). Our observations at the site showed a thick and widespread ash cover immediately post fire (Fig.1)” — this statement cannot be supported by the current quality of Figure 1.

•    Figure 1b is too dark, and the meaning of the different bounds of the Wombeyan Karst Reserve is unclear. Are these administrative, geological, or hydrological? This is important to clarify.

•    Figure 1d: Consider whether the information content justifies its current size.

I strongly recommend revising and improving Figure 1.

Figure 2: 

There is an inconsistency in the time span: the axis text states 1961–1990, while the figure caption refers to 1961–1991. Please clarify.

Figure 4b:

•    Please include a description of the line in the caption—why is there only one line?

•    Indicate clearly which number represent which period. You could use red to highlight the post-fire period, consistent with Figure 4a.

•    Why were both periods plotted together in one panel, unlike Figure 6, where they are shown separately?

Discussion: While the concise writing style is appreciated, the manuscript would benefit from a broader contextualization of the results. I would like to have a broader discussion of the results and on the implications of fire impacts on the hydrological cycle, an area of increasing interest, see e.g. Guzmán-Rojo et al. (2024) or Moazeni and Artemi (2024).

  

Secondary Comments

L19: Remove one period.

L43: Balfour et al., 2014

L68: The whole cave is less than 4 m depth below land surface -> 4 m deep or rephrase

L97: Remove one period.

L111: pre-fire

Table 1 caption: Consider using a symbol (e.g. an asterisk) instead of italics to improve readability. 

Table 2 caption: Climate (Köppen-Geiger)

References:

Guzmán-Rojo, M., Fernandez, J., d’Abzac, P., & Huysmans, M. (2024). Impacts of Wildfires on Groundwater Recharge: A Comprehensive Analysis of Processes, Methodological Challenges, and Research Opportunities. Water, 16(18), https://doi.org/10.3390/w16182562.

Moazeni, S., and Cerdà, A. (2024).  The impacts of forest fires on watershed hydrological response. A review, Trees, Forests and People, Volume 18, 2024, https://doi.org/10.1016/j.tfp.2024.100707.

Main comments

The paper reanalyses an existing data set about the response of the soil and rock above a shallow cave to rainfall before a controlled fire consumed the vegetation, and after. Drip monitors in the cave are used to determine when groundwater recharge occurred.

The paper is brief, generally well-organized, and reasonably clear (more on that below).

Lines 58-61 give the objectives of the paper. Objective 1 is well covered by the paper, but the other objectives are less convincingly addressed.

The Discussion and Conclusions are overall a bit qualitative. Is it possible to estimate quantitative effects on recharge and overland flow? I presume that a fire reduces transpiration (T) and increases evaporation € until the vegetation is restored to a leaf area index that gives a similar partitioning of infiltration in E and T as the pre-fire vegetation. Can you say anything on that? Given the nature of your data, I realize this may not be doable. On the other hand, the fire was controlled., so perhaps there were other sensors in place that permit a more quantitative analysis.

Is it possible to verify, from field observations, that ash filled the cracks, just as you were able to verify the formation of an ash crust?

The discussion is a bit brief. I am not sure it extracts all the information from the data. For instance, do you generally see increased and earlier discharge peaks in streams within the first months after extensive bushfires? That would support the hypothesis of panel 2 in Fig. 8. Did you find as deposits at (some of) the drip zones in the cave? That would indicate the cracks are losing their ash, and also point to cracks that are continuous from the soil surface to the cave. Is there a difference in the evolution of the drip rate over post-fire time between drip locations with and without such ash deposits? That could point to different ash removal rates from deep and shallow fractures (or something entirely different).

The captions of the figures and tables are insufficiently informative to allow figures and tables to be read independently of the text. Even after reading the text, they are not very clear. Several figure captions only repeat the label of the vertical axis, for instance, and abbreviations/acronyms are not explained. Abbreviations appearing above columns in a table are not explained in the caption of the table. Also, I have seen different box-and-whiskers plots, better to explain all the features of these plots. Some do not appear to have whiskers (Fig. 6) – what is going on there? Careful rewriting, keeping in mind that readers should be able to understand figures and tables before perusing the main text, is needed.

Figure 8: By what mechanism is ash removed from fractures, once it is in? 

Minor comments

Please check for double periods (..). I saw one, but there may be more.

There are elements of the discussion sprinkled in the Results section. Either combine the Results and the Discussion sections, or more rigorously separate the discussion from the results.

Fig. 8. Typos in the text below panels 1 and 3. In the caption, ‘More’ should not have an upper case M.

L. 42: How is the carrying capacity defined?

L. 88: ‘very high’: depends on your reference frame, I suppose.

L. 100-118: These are all results, although this is the methodology section. I understand that these results are form Bian et al. (2019). If that is the case, please clarify this a bit better, perhaps by making this segment a separate paragraph with a leading sentence indicating that you are summarizing the main findings of the pre-fire and post-fire hydrology of the site as presented by Bian et al. (2019).

L. 153-154: Different pieces of precipitation data gave similar results, but earlier you stated there was a 28% difference between them. How can that be?

L. 159-164: Is this not methodology, rather than a result?