Hannaford et al. use a large sample of stream gauges in the UK to assess whether hydrological drought properties and low flows have changed in recent decades as well as at longer time scales. They place the results of their analyses in the context of climatic and water/land use changes and suggest that evidence for worsening drought is minimal, especially amongst many confounding influences from human impacts. I commend the authors for the work they have presented here, but believe that substantial edits are required to clarify results as well as to more fully address the influence of human water and land use on drought properties and low flows. I believe that these edits will lead to a paper that will be of interest to the broad readership of HESS.

Comments and suggested edits bulleted below:

• Please check for consistency in author affiliation, postal code etc.
• Please write out all abbreviations in figure captions. As written currently, it is hard for the reader to understand the content of the figures without referencing the text repeatedly.
• Figure 4 legend symbol up down is opposite of what is shown on the maps for intensity and deficit.
• Color scale for figure 6 is the reverse of intuition or the statistic seems reversed. Prior trend plots showed drought properties becoming longer and more intense through time in the south and shorter and less intense in the north.
• Current figure 6 with the legend interpreted as shown implied that for trends tests starting and ending in more recent years, accumulated drought deficit has increased significantly for several sites in the north. Cree, Allen, Ellen as examples.
• There are several studies that I believe should be cited in the introduction and discussion to more thoroughly place the present study in the context of other recent studies on hydrological drought patterns and trends:
  • Brunner, M. I., Swain, D. L., Gilleland, E., & Wood, A. W. (2021). Increasing importance of temperature as a contributor to the spatial extent of streamflow drought. Environmental Research Letters, 16(2), 024038.
  • Dudley, R. W., Hirsch, R. M., Archfield, S. A., Blum, A. G., & Renard, B. (2020). Low streamflow trends at human-impacted and reference basins in the United States. Journal of Hydrology, 580, 124254.
  • Hammond, J. C., Simeone, C., Hecht, J. S., Hodgkins, G. A., Lombard, M., McCabe, G., ... & Price, A. N. (2022). Going beyond low flows: Streamflow drought deficit and duration illuminate distinct spatiotemporal drought patterns and trends in the US during the last century. Water Resources Research, 58(9), e2022WR031930.
  • Konapala, G., & Mishra, A. (2020). Quantifying climate and catchment control on hydrological drought in the continental United States. Water Resources Research, 56(1), e2018WR024620.Please capitalize the first word of figure caption in every figure caption.
  • Tijdeman, E., Barker, L. J., Svoboda, M. D., & Stahl, K. (2018). Natural and human influences on the link between meteorological and hydrological drought indices for a large set of catchments in the contiguous United States. Water Resources Research, 54(9), 6005-6023.
  • Van Loon, A. F., & Laaha, G. J. J. O. H. (2015). Hydrological drought severity explained by climate and catchment characteristics. Journal of hydrology, 526, 3-14.
• Figure 8 what does s in figure caption stand for? What is BFIHOST?
• Considering the extensive research and monitoring program that the authors are using for this research, I find the analysis and discussion of human impacts on drought and low flows to be incomplete. Are there not spatial datasets that report on the changing patterns of water withdrawals, impoundments, land use changes that would make it possible to more fully assess how trends in streamflow signatures have been impacted by human flow regulation, land use change, and groundwater regulation for individual watersheds as well as the aggregate response across regions? This would substantially extend the impact of this paper.
• Tabular summaries of the fraction of all sites and fraction of least disturbed sites with significant trends in low flow and drought metrics are needed. Preferably at least splitting into northern and southern UK regions, as well as into classes of land use / land cover (e.g. agricultural, forested, urban, heavily regulated by dams). These tables would help to synthesize the main results displayed in the figures in a way that makes digesting these results easier for the reader, and could also enhance the analysis of human impact on hydrological drought properties and low flows in the UK. See Dudley et al. (2020) as an example:
  • Dudley, R. W., Hirsch, R. M., Archfield, S. A., Blum, A. G., & Renard, B. (2020). Low streamflow trends at human-impacted and reference basins in the United States. Journal of Hydrology, 580, 124254.

Title: have river flow droughts become more severe? A review of the evidence for the UK – a data-rich, temperate environment

Authors: Hannaford et al.

Summary

This paper presents a review and extended analysis of streamflow drought in the UK based on a dense network of observed river discharges across all NRFA catchments. First, the study analyzes changes in drought severity across the UK using observed data, followed by an extended analysis with reconstructed data. Second, the paper explores key drivers of streamflow drought, focusing on climatic and human influences. The authors found little evidence that drought will become more severe, which contradicts near-future climate projections and anticipated human disturbances. Furthermore, they also highlighted some recommendations for researchers, policy makers, and water managers on moving forward.

Assessment

This paper presents new evidence that challenges the notion of worsening drought over recent decades due to climate change. The analysis is based on the in-situ observational data, which provides a reliable basis for the findings. However, while these findings may be specific to the UK, and not directly applicable to many regions (e.g., southern Europe), the authors argue for their broader relevance. The manuscript is interesting and well written. I have a few minor comments below and three general comments, but only for clarification and improvement. I believe this work is well-suited for publication in HESS.

General Comments

I have three general comments regarding the manuscript, all aimed at clarification, suggestion, and improvement.

1. As mentioned above, the findings of this study may be specific to the UK. Numerous studies have highlighted that drought will be more severe in southern European regions. I suggest that the authors reconsider their statement about the broader relevance of their findings or specify which aspects of the findings may have broader applicability.
2. I recommend incorporating more quantitative results instead of qualitative descriptions. The authors tend to present their results in a qualitative way e.g., only mentioning increase or decrease without providing precise percentage changes in trend magnitude (see Fig. 2).
3. There is inconsistency in the presentation of result, especially for Figure 5. The authors used SSI-3 in Figure 4, SSI-12 in Figure 5, and then return to SSI-3 in Figures 6 and 7. If possible, I suggest to replace SSI-12 in Figure 5 with SSI-3, as the author of Figure 5 is also a co-author of this paper.

Line by line comments

L refers to line and P refers to page.

P2L48-56: I suggest moving the second paragraph to the end of introduction. This paragraph presents the objective of the study, and in my opinion, it is disturbing the flow of introduction.

P3L80: Maybe place a comma before “it is necessary to quantify…..”

P3L85: What do the authors mean with “international standard”?

P4L122: I am wondering how we can define accumulation deficit for SSI? From my understanding, accumulation deficit can be applied only for threshold approach.

P12L324: Maybe place a comma before “there is generally a contrast…..”

P15L392: Please provide example of literatures/references when you say many literatures.

P15L398: Write the abbreviation of East Atlantic “(EA)” here since it is the first time EA is mentioned.

P15L415: What is SCA?

P20: Figure 8. In the figure caption, please use letter a and b instead of top and bottom. Also, please explain what N, G, S, GS, and others are.

P20L569: Here the authors write “It follows that….” As opening paragraph. What “it” refers to?

P21L587: Maybe place a comma before “LULC have been very…..”

P22L629: Maybe place a comma before “it is important not to…..”

P22L645: What do the authors mean with “cold comfort”? Also maybe write “….who are already frustrated….”

P25L740: I think you should reduce the jargon “smoking gun”

P25L741: Put comma and remove second “in fact” -> In fact, the key finding is that there is little evidence….

P36L1125: It seems that the sentence is not finish. “Seasonal flow”