This paper presents 15 years of curated in situ soil moisture time series from the SwissSMEX network and demonstrates how data from 12 grassland stations, providing volumetric soil water content at multiple depths and integrated values down to 50 cm, can be used to analyze drying trends in soil water content. The data set is of broad interest given the increasing occurrence of drought in many regions worldwide under global climate change and fits well within the scope of ESSD. The presented data product will be valuable to the scientific community working on global change and water scarcity issues in alpine regions. It would be great to also include the data in the International Soil Moisture Network (Dorigo et al., 2021).

Unfortunately, the manuscript exhibits several substantial shortcomings with respect to its methods, content, overall structure, and clarity of writing, which need to be addressed in detail (see specific comments below). I have suggested improvements to the text in some places. However, the entire text should be revised by a native speaker. When revising the manuscript, authors should bear in mind that ESSD focuses on the data set rather than on the interpretation of the data.

General comments:

The Abstract is overly long and not suitable for ESSD. It should be 150–200 words and focus on the dataset rather than scientific interpretation, describing the data type, size, and spatial and temporal coverage, explaining how the data were collected, briefly outlining quality-control procedures, and clearly indicating where the dataset is available (e.g., repository or DOI).

The Introduction section is too long and includes discussion, which is inappropriate for ESSD. It should instead concisely provide context and justify the dataset by highlighting gaps in existing data, clearly state the dataset’s purpose, scope, key variables, and coverage, and emphasize its value.

The Conclusion section should be shortened and focus on the dataset rather than scientific interpretations, emphasizing its main contributions, unique features or improvements over existing datasets, and briefly noting potential applications.

The manuscript does not provide sufficient references and details for the statistical methods used. Even well-known methods such as the Mann-Kendall trend test should be properly cited and the implementation described (e.g., software/library and version). For example: “The Mann-Kendall test (Mann, 1945; Kendall, 1975) detects monotonic changes over time and is robust to non-normally distributed data. Calculations were performed using the Python library pyMannKendall (vX.Y.Z) at α = 0.05, with missing values handled according to the library’s default options.”

A map showing the locations of the measurement stations should be included, along with a table summarizing key soil properties, such as soil type and texture.

Specific comments:

L10: “curated time series of in-situ”

L16: “vertically integrated” or “root-zone soil moisture”

L16: “the robustness of recent drying trends”

L44-59: This section reads more like a discussion and is not directly related to the data presented; it should be rewritten in a more concise way.

L45: Is the increase in evapotranspiration significant?

L53: “soil moisture”

L117: Please explain the trapezoidal method.

L115-143: This section on data processing is very confusing. The processing steps are not clearly presented, and information on data processing, e.g. sensor calibration and data correction, is missing. It needs to be rewritten in a clearer and more concise manner, with the focus on how the data was processed.

L164: “0–0.5 m (merged)” should be removed, as this information is unnecessary; the acronym IWC is self-explanatory.

L165: Please clarify how this percentage was determined. Was a statistical analysis performed to derive it, or was it determined in another way?

L184-186: This section should be moved to Chapter 2.1.2. In addition, the weighting function should be presented as a numbered equation. Note that the weights in the equation should not have units of length, otherwise the unit of IWC would be mm·m rather than mm. Combining several measurement depths into a single layer (e.g., 7–28 cm) causes measurements at 5 cm depth to be weighted more heavily. It would be preferable to weigh each measurement depth individually when calculating IWC.

L186: This is a strong assumption and should be tested using periods for which deeper soil moisture measurements are available.

L188–193: Since these data are not part of the dataset provided with this submission, this section is too excessive and should be reduced to a single sentence.

L199: “in-situ time series”

L201: "available on a 0.25° × 0.25° latitude–longitude grid with daily temporal resolution."

L211: “Figure 3 presents the individual soil moisture anomaly time series of the summer IWC at SwissSMEX stations (2010–2024) for each station combination (Table 1), along with the respective median anomalies.”

L214–215: The median anomalies appear to exhibit different trends. Please add trend lines to make these differences more clearly visible.

L234: Please explain “Theil-Sen trend”

L284-285: “ERA5-Land and ESA CCI PASSIVE also show good agreement in the long-term monthly variations of Swiss Plateau soil moisture since 1991…”

L295–299: This summary section does not fit in the Discussion and should be removed.

L329–330: Domínguez-Niño et al. (2019) found no evidence of decreasing sensitivity of the 10HS sensors in detailed laboratory experiments with different soil materials. However, using only the factory calibration led to much higher measurement errors compared to sensor- and soil-specific calibrations, which could falsely suggest a decrease in sensitivity. This important clarification should be included here.

L341-342: “We present a curated and comprehensive set of in situ soil moisture time series from the SwissSMEX stations on the Swiss Plateau.”

Figure 1: This figure only shows snapshots of data availability. A time series diagram illustrating the availability of measurements over time would be more informative (see, for example, Fig. 2 in Bogena et al., 2022).

Figure 2 does not effectively present the data. The many overlaid lines make it difficult to distinguish individual series, and the thick black line is superfluous, as it merely duplicates other datasets. I suggest presenting the data in two additional subplots. In addition, the legend could also be placed outside the plot area so that the data range does not have to be unnecessarily restricted. Finally, similar plots should be provided for the remaining stations in the supplement.

Figure 4: The numbers inside the circular areas are not all easily readable and should be made clearer.

Literature

Bogena, H.R., M. Schrön, J. Jakobi, P. Ney, S. Zacharias, M. Andreasen, R. Baatz, … and H. Vereecken (2022): COSMOS-Europe: A European network of Cosmic-Ray Neutron Soil Moisture Sensors. Earth Syst. Sci. Data 14: 1125–1151. DOI: 10.5194/essd-14-1125-2022

Domínguez-Niño, J.M., H.R. Bogena, J.A. Huisman, B. Schilling and J. Casadesús (2019): On the accuracy of factory-calibrated low-cost soil water content sensors. Sensors 19(14): 3101. DOI:10.3390/s19143101

Dorigo, W., I. Himmelbauer, D. Aberer, L. Schremmer, I. Petrakovic, L. Zappa, W. Preimesberger, A. Xaver, F. Annor, J. Ardö, D. Baldocchi, M. Bitelli, G. Blöschl, … and R. Sabia (2021): The International Soil Moisture Network: serving Earth system science for over a decade. Hydrol. Earth Syst. Sci. 25: 5749–5804. DOI:10.5194/hess-25-5749-2021

The manuscript and data are fitting to the scope of ESSD. They are about an observational dataset of soil moisture data in Switzerland. The authors present in situ data from volumetric soil moisture that are used to estimate the integrated soil water content. They further validate their data and results of a trend analysis with model data (ERA5 Land) and a remote sensing product (ESA CCI). 

The manuscript would benefit from a streamlining of the storyline. Currently the manuscript is divided into a results, discussion and conclusion section. The discussion section includes in major parts results and isn’t discussing the results from the results section with exception of a few points. The presented results can be discussed more in depth to support the analyses that have been presented in the results section. Further some figure captions are repeated in the text which elongates the paper unnecessary. The conclusion section is mainly a summary rather than a conclusion section and would benefit from some overhauling.

Also also suggest to show some of the maths used for calculating for example IWC and correction/homoginization of the IWC time series.

The manuscript will be well placed in ESSD after some work into streamlining the storyline. It highlights important points like the difficulties of funding and maintaining long-term observational networks and their benefit for climate impact assessment studies. It showcases ideas how to deal with short time series and ways of bringing observations from various instruments together.

Specific Comments:

Can you please add a map of the locations of the stations and add the footprint of the ERA and ESA CCI. data

• L140-144 Can you please elaborate on the scaling one time series with the other using mean and standard deviation. Ideally add the formula. 
• Figure 2: 
• Panel a) is hard to read. It might be useful to move the IWC up to have an better view on the VWC
• the figure caption is quite hard to understand
• L186: assumption VWC28-100cm  
• Can you please elaborate on the meaning of Figure 4? What is the take home message of the pairwise correlations?
• L237 for the trends calculated between -0.1 % year-1 and -1.2 % year-1 it would be useful to discuss the accuracy of the measurement devices. This enables the reader to assess the relevancy of the detected trends.
• Figure 5: Can you please increase the font size of the labels and caption? I am not sure if the figure needs to start in 1980. I would suggest zooming in to 2010-2025.

Data:

Thanks for including metadata like the soil texture and land cover into the data repository. This is very helpful.

• Can you please provide the SiteInfo_SwissSMEX.pdf as ASCII file. This makes it machine readable and hence easier to work with.
• It would be useful to get a lookup table for the nomenclature in the header columns. I know; it can be worked out from the file headers. I would appreciate a dedicated lookup table though.