Exploring Nature-based Solutions in Mountain Regions: A Review of Their Hydrological Functions

Fernández Velarde, Michell Andree; Cools, Jan; Staes, Jan; Yepez, Santiago

doi:10.5194/egusphere-2026-744

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https://doi.org/10.5194/egusphere-2026-744

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26 Feb 2026

| 26 Feb 2026

Status: this preprint is open for discussion and under review for Hydrology and Earth System Sciences (HESS).

Exploring Nature-based Solutions in Mountain Regions: A Review of Their Hydrological Functions

Michell Andree Fernández Velarde, Jan Cools, Jan Staes, and Santiago Yepez

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.

Received: 09 Feb 2026 – Discussion started: 26 Feb 2026

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.

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Michell Andree Fernández Velarde, Jan Cools, Jan Staes, and Santiago Yepez

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RC1:
'Comment on egusphere-2026-744', Anonymous Referee #1, 13 Mar 2026 reply
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:
The two research questions and objectives outlined in the introduction (lines 53–55) could be more closely aligned with the topic stated in the title and abstract. Based on the title and abstract, a stronger focus on analysing the hydrological functions of NbS might be expected, rather than primarily presenting descriptive results from the literature review.

The methods and results of the literature review are described very extensively with 14 figures. Can these sections be condensed to only the relevant findings for the main study aim (i.e. the hydrological functions of NbS) and figures reduced to the most important aspects/findings? I would focus on those aspects, which are picked up later in the discussion section, hence only those results which give a clear and robust information on ‘the hydrological function’ and effectiveness of NbS measures. Many of the bar graphs (e.g. Fig. 4, 5, 7, …potentially others) could be expressed in word, in one sentence, which would help to further condense these sections.

I see chapter 4.6 to be the central part of this study. However, it was not entirely clear to me how the findings in figures 11, 12, and 13 are linked to the literature review. If I understood correctly the indicators were taken from the reviewed studies, but what about the links (-/+ relationships)? It could be insightful to add another layer of information to the figures by quantifying these relationships further (e.g. visualizing by the thickness of the arrows how many studies found positive/negative/no/diverging relationships). In their current form, the figures provide limited additional insight beyond the information and conceptual understanding already known.

Some of the relationships illustrated in figures 11, 12, and 13 may benefit from additional clarification. For example, in the wetlands section, the positive relationship between topography and water retention capacity and the negative relationship between topography and runoff appear somewhat counterintuitive and could be explained in more detail. It would also be helpful to clarify why no connections are shown between topography and soil erosion, or between soil and soil erosion.

Regarding the quantification of NbS effectiveness, lines 317-326 stand out positively. This section provides a level of detail that can be particularly valuable for decision-makers when evaluating such interventions, and for scientists aiming to test and further assess these reported impacts. Would it be possible to extract more such information from the reviewed literature?

Specific comments:
I would suggest reducing the number of figures substantially and focus on the most important ones.

Figure appearance: I would ensure the figures have an appropriate size and are not distorted (e.g. Fig. 8 – maps). The figures appear to have been produced in Microsoft Excel. Excel is a perfectly valid tool for generating figures, which I do not mean to discard, but the visual presentation could be improved for publication in a scientific journal. The authors might consider recreating them using software more commonly used for scientific visualization (e.g., R or Python), as these tools allow figure sizes, styles, and font sizes to be easily standardized across all figures.

Figure 15: are all the relationships equally strong (= same thickness of arrows)? Can the message of this figure be presented in a more refined way?

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.

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Citation: https://doi.org/10.5194/egusphere-2026-744-RC1

Michell Andree Fernández Velarde, Jan Cools, Jan Staes, and Santiago Yepez

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https://doi.org/10.5194/egusphere-2026-744-supplement

Michell Andree Fernández Velarde, Jan Cools, Jan Staes, and Santiago Yepez

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Short summary

Water security in mountain regions is under threat, yet evidence on the effectiveness of nature-based solutions is limited and inconsistent. Our review of global studies clarifies their hydrological benefits and highlights gaps, particularly the frequent omission of local knowledge and climate change scenarios. These findings highlight the need for more inclusive methodologies to transform these natural strategies into reliable, equitable tools for safeguarding mountain water resources.


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