the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 Feb 2026
Exploring Nature-based Solutions in Mountain Regions: A Review of Their Hydrological Functions
Abstract. Mountain regions play a fundamental role in sustaining the water supply for many activities around the world. However, these ecosystems are under increasing pressure due to climate change, changes in land use, and socioeconomic stressors, threatening water security. Implementing Nature-based Solutions (NbS) in mountain catchments are considered and effective means to increase water security, in the mountain regions itself, but also downstream. Despite growing interest, the scientific evidence base on the hydrological impacts of NbS in mountain regions is limited and characterised by methodological inconsistencies and insufficient consideration of climate dynamics. This study aims to review the hydrological performance of NbS in mountain regions and identify key knowledge gaps. We present a typology covering Wetlands, Forest-based interventions (Afforestation, Reforestation, Forest Conservation, and Agroforestry), and Water Harvesting interventions highlighting their hydrological functions. The analysis revealed that the most frequently reported indicators included flow regulation, groundwater recharge, water retention capacity, and soil erosion control. Our findings emphasise the need for more standardised methodologies in this environment, to enable robust comparisons of NbS performance under future scenarios. Strengthening the evidence base will require methodological integration and multiscale analyses that incorporate climate variables, as well as the inclusion of local and indigenous knowledge in planning and evaluation processes. Such efforts are essential for enhancing the design, implementation, and long-term effectiveness of NbS strategies for safeguarding water resources in mountain regions.
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Status: open (until 10 May 2026)
- RC1: 'Comment on egusphere-2026-744', Anonymous Referee #1, 13 Mar 2026 reply
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RC2: 'Comment on egusphere-2026-744', Anonymous Referee #2, 28 Apr 2026
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Review of the paper submitted to HESS by Velarde et al. entitled “Exploring Nature-based Solutions in Mountain Regions: A Review of Their Hydrological Functions”.
Please see my review comments organized by sections of the paper that follow:
Abstract is very vague with few specific findings.
Introduction:
L 26: Water towers typically refer to some of the highest peaks where snow, glacier & permafrost melt are the primary runoff contributors.
L 40-46 It is not at all surprising that IUCN does not adequately address water issues in the context of NbS; IUCN mostly focuses on biodiversity and conservation.
L46-51 Likewise the EC approach is yet another indicator approach with little emphasis on hydrological process linkages.
L54-55 The second objective listed here seems liked a flawed approach to me – firstly, most indicator approaches do not consider processes in sufficient details and secondly, standardizing these would add yet another level of disconnect from reality.
L56-57 The stated focus on water security seems to get lost in the results that are later presented.
Nature-based Solutions Definition:
This short section comes across as initially very general (i.e., the OECD definition of NbS) followed by a rather restrictive application – only looking at water in the contexts of forest conservation, wetland restoration, and water harvesting. It seems that the potentially greatest benefits from NbS are ignored – e.g., reducing overland flow and increasing infiltration to alleviate surface erosion, support baseflow in streams, and reduce peak flows (although later in the paper soil erosion is marginally addressed). Also, no mention of water-induced or mediated hazards – an area where NbS can offer significant benefits. As such, it almost seems like categories of water-related NbS were selected based on this automated literature search rather than a pragmatic assessment of where NbS could offer the most benefits.
Methodology:
These automated ‘scoping reviews’ of the literature without including critical insights are becoming far too common in papers. They reveal very little important process information. Of course, screening criteria were used to help fit your pre-designated “forest conservation, wetland restoration, and water harvesting” focus. However, I fail to see the innovation here. Even with this automated approach, you missed several key, recently published NbS papers that deal with NbS interventions in mountain environments.
L103 Ignoring publications that are not in English is somewhat understandable but nevertheless injects potential bias.
Results:
Section 4.1
This section only presents a summary of the automated reviews based on the authors predetermined structuring of the criteria. Lots of simple graphs and a literature map, but, once again, I do not see much innovation here.
L125-126 Of course more recent publications will be less cited.
Section 4.2
I understand the connection with NbS and societal issues, but this begs the question of why a broader approach to water-related NbS was not used in this paper. Overall, this short section contributes few new insights.
Section 4.3
Similar to my comments on Section 4.2, simply categorizing NbS as including or not including indigenous knowledge, provides few new insights.
Section 4.4
These very brief results suggest better documentation of climate change impacts in NbS studies are needed, but with no other recommendations. What is really needed in NbS interventions is granular scale climate assessments and these are incredibly difficult to capture in mountainous terrain.
Section 4.5
L210-213 I may be wrong, but I have a hard time believing that studies on wetlands covered the largest scale – this could be an artifact of the total catchment areas, but it is difficult to comprehend that wetlands covered larger areas than forest conservation and water harvesting NbS interventions; or it could simply be a bias of the types of reported studies. In any case, it does not seem logical.
Section 4.6
Generating a set of NbS indicators based on this automated literature search and the reported metrics is not solidly grounded in hydrological processes and it could possibly set dangerous or erroneous precedents.
L246-253 This contains several examples of why such automated reference searches leave knowledge gaps. The hydrological controls noted are mostly obvious relations that are covered in any introductory hydrology textbook. Soil erosion is now mentioned, but no new insights are presented.
Section 4.7
One concern here with this type of analysis is that most studies tend to publish positive results while few publish negative results. This will bias such an analysis. One example herein is the discussion of the erosion control benefits of terraces – this is not always the case and terraces can exacerbate landslide erosion and even surface erosion under certain circumstances. Nevertheless, this sub-section is more informative than the previous six sub-sections of the Results.
Discussion:
L349-352 I question whether developing NbS strategies at individual sites or areas is a negative as implied. These NbS interventions typically address several issues – not just the three water related issues noted in this paper – and thus they need to be carefully developed for specific areas, including concerns related to climate, soils, anthropogenic stressors (including legacy effects), hydrology, native vegetation, and the potential for NbS to address these in a holistic manner that supports local livelihoods.
L362-375 I would argue that NbS ‘strategies’ have been used for many decades going back to the integrated catchment management practices of the 1970’s – yes, they had a different name and may not have been as sophisticated, but implying the Chinese scientists are leading this field is not accurate. Most of the work you see published is relying heavily on earlier research that may not have been called NbS investigations, but nevertheless provided the backbone for the more recent papers – there is nothing wrong with this, except for the impression that all of the papers you cited represent unique research.
L376-383 NbS should address both restoration of ecosystems as well as societal benefits. This is a complex, granularly- focused task and is why broad ‘one-size-fits-all’ NbS interventions will not work.
Section 5.2 The ecosystem services cascade approach is worthy of consideration, but it is far too simply addressed here.
Section 5.3 Some good ideas here, but it is difficult to see if any of these were derived from the literature search.
Section 5.4 I see no new insights here; the statements in L420-424 could apply to most studies in mountainous terrain where climate change predictions are of little value compared to the more granular needs of NbS applications and the societal benefits that could be derived from these.
Section 5.5 The first sentence addresses my previous point – i.e., most NbS strategies need to be designed for specific areas with granular biogeophysical data along with site specific socioeconomic concerns and information.
L434-440 The call for applying multiple methods to address NbS is a good point, but certainly not unique, as this is a well-recognized approach in transdisciplinary investigations.
Section 5.6 The first referenced sentence encapsulates a major point I have been making in this review – i.e., the biogeophysical characters and societal context of individual sites need to define the NbS strategies. But in the next sentence the authors express disagreement with this statement saying this automated literature review and analysis “demonstrate a consistent pattern among NbS types, while also highlighting significant methodological gaps”. Saying that such an empirical automated approach provides new insights into such patterns is not justified nor established in this paper.
Conclusions:
Most of what is presented here has already been addressed in my preceding comments.
Citation: https://doi.org/10.5194/egusphere-2026-744-RC2
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The paper is titled "Exploring Nature-based Solutions in Mountain Regions: A Review of Their Hydrological Functions“. This is an important topic and of high relevance, considering the ongoing and rapid changes in mountain hydrology and their associated impacts for mountain communities. As the authors point out correctly, evidence of the effectiveness of Nature-based Solutions (NbS) in mountain regions is still limited and a strengthened and robust evidence base is needed to systematically assess the impacts of such measures. While the title and abstract clearly define the main aim and scope of the study, the manuscript would benefit from a clearer and more focused storyline that better aligns with the title and abstract. At present, some sections of the text seem to diverge from these central objective. The manuscript moves between topics such as a detailed description of the methodology of the literature review, to an extensive yet mainly descriptive presentation of the review results, a conceptual summary of potential hydrological functions of NbS, as well as a discussion of limitations of NbS measures regarding climate change aspects and the inclusion of Indigenous and local knowledge. As a result the focus promised in the title (‘ a review of hydrological functions of NbS in mountain regions’) gets lost and the overall storyline needs more coherence and focus.
Overall, I would suggest a thorough revision of the manuscript with the aim of further refining and focusing its overall scope and objectives. If the intention is to discuss the hydrological functions of NbS, this focus should be reflected in the research questions and in a more quantitative/robust presentation of the results. Alternatively, if the primary goal is to identify gaps in the current NbS research/literature, this focus could be more clearly reflected in the title and in the main aim outlined in the abstract.
Below are several suggestions that may help to further focus the paper on the topic outlined in the title and the abstract, which in my mind would help to improve its impact and visibility.
General comments:
Specific comments:
Considering the points raised above, I am unable to recommend the publication of the manuscript in its current form. However, I hope the authors view these comments as constructive and helpful for further developing and strengthening the manuscript. I would like to emphasise again, that the topic is highly relevant and a more focussed presentation and discussion could lead to a highly impactful article. The title could be a nice guide to focus the study on a single relevant question: exploring the hydrological functions of nature-based solutions in mountain regions.