Editor's choice 

This paper introduces recent methods to cluster catchments that is based on traits with an application on a very important dataset (over 9000 catchments using 274 traits). The method proposed open many research perspectives in the fields of hydrology, environmental sciences and other disciplines.

Freshwater is a precious commodity for mankind, and irrigation is one of the largest component of freshwater usage by mankind. Many uncertainties exist in determining the amount of freshwater usage for irrigation. This manuscript discusses various ways to quantify irrigation and application of remote sensing to assess irrigation fluxes. With future, high-resolution remote sensing platforms becoming available, this work will be helpful to develop application pertaining to irrigation quantification especially is drought affected and semi-arid regions of the world.

This review paper constitutes a tremendous effort reviewing and analyzing a vast body of literature on the evaluation of Satellite Remote Sensing-based evapotranspiration datasets. It is a great road map for this field of research guiding all future such studies toward the use of community-based best practices.

This paper is relevant and can be of interest for a wider audience. It is important that the effects of artificial snow on hydrology and water resources is discussed in a more technical, hydrological forum, like HESS. The paper shows important and sound conclusions which are relevant in the societal discussion on the effects of snowmaking.

This paper presents an open-source software package for earth observation data accessing, reformatting, and visualization. This tool can be useful to the broad science community and stakeholders for effective use of remote sensing products. It lowers the technical barriers and simplifies the process of accessing earth observation data. It works for multiple operating platforms.

The characterization of subsurface hydraulic properties of catchments is one of the grand challenges in hydrology. This study explores the potential of using the stream network for this issue. The idea is very innovative and deserves to be highlighted.

The study proposes a new approach to characterize soil hydraulic functions. The novel approach strongly improves simulation results. This is a significant advancement of vadose zone hydrology.

The quest for low-carbon energy sources is driving a wave of new hydropower dam construction throughout the world. This is particularly the case in mountain regions such as the Andes, where a very large, untapped potential for hydropower still exists. It is therefore essential to get a better grip on the side-effects of dam development, and their impact on water quality is a very important but highly understudied aspect of those. This is again particularly timely and relevant in tropical regions, which are facing a perfect storm of limited data availability, poorly understood processes, and major challenges for sustainable development.

Understanding how catchments respond to change is a central theme of the work of many hydrologists around the world, however, it is fair to say that the vast majority of these studies have focused on water quantity. This study is unique in that it represents a very detailed treatment of how water quality changes due to drought, which is a topic that is becoming ever so important with the rapid changes happening in warming climate for many regions of the world. The authors very cleverly combine both complex models and data-driven analyses to elucidate the effects of extreme drought on river water quality.

In agreement with the handling Editor, the study is highlighted in HESS

This work addresses the important issue of the "dry gets drier wet gets wetter" paradigm from a new perspective using terrestrial water storage estimates. The paper can be an important contribution to the debate on how climate change will impact the global distribution of aridity.

This is highly relevant research on a topic that has great socio-economic impact. The research uses state-of-the-art observational networks and drought simulation, which could inspire similar efforts in other European countries.

This is a paper demonstrating the added value of hybrid modeling approaches for modeling hydrological features (flow and internal states). The paper is well written and will be sent out for a detailed scientific review. The combination of ANN with ODE-based hydrological models is a good way forward to construct hybrid modeling approaches. It is a significant step forward compared to the current state of the art.

I recommend this paper for highlight. In the words of the authors: "No previous study has been able to provide such detailed data [of soil moisture] at catchment scale, amount of terrain indices in combination with an extensive field survey which clearly demonstrates the importance of selection of terrain index, DEM resolution and index-specific threshold.

As also stated by both reviewers, this work is important and timely. It combines data from several sources to highlight the role of fine-scale hydrogeological features on hydrological processes. As nicely stated by reviewer 2: “The work addresses important questions regarding the description of connectivity and interaction between groundwater and surface water in mountainous catchments. The authors develop in their paper an interesting vision at the interfaces between geomorphology, hydrology and hydroecology (principally fish habitats)

The authors present a new method to sample water vapour from trees in a cost-effective manner. The method can be applied in a lab, but also in the field. As many scientist are struggling with proper sampling method, I think this paper is worth highlighting.

The study provides a unique effort undertaken by several research groups in the context of a remarkably instrumented large scale system. The latter is subject to a variety of measurement approaches and techniques and a wide range of models are considered in a remarkable inter-comparison study. Key methodological elements stemming from this very comprehensive work are highly relevant to the broad hydrological community.

The paper presents an original and innovative approach to understand hillslope processes linking hillslope surface flow, drainage structure formation, and erosion processes to thermodynamics. I consider that the topic is very important in understanding why simple parsimonious empirical methods work in nature.

The paper provides interesting insight about the relative importance of local land use change versus climate change effects on sediment delivery to surface waters at a decadal time scale.

How vegetation responds to changing climate will have large implications for our global carbon and water cycles. This study shows the potential of using C-band scatterometer data to investigate vegetation status-- with over a 30 year record. Many applications related to biosphere-atmosphere interactions could potentially develop from here and improve weather and climate predictions, and model evaluation in terms of their representation of vegetation dynamics.