Manuscript title: ‘Integration of the Global Water and Lake Sectors within the ISIMIP framework through scaling of streamflow inputs to lakes’;

Manuscript ID: egushpere-2025-3126;

Authors: Ana I. Ayala et al.;

Target journal: Geoscientific Model Development.

This work integrates the stream flows from the nearby catchments into 71 lakes in Sweden, based on the scaling method of the global water and lake sector model. The model performances are compared with referenced model results and observed data from stations. The authors finally concludes that the updated model is satisfactory on modeling the streamflow. The authors have done a good work in explaining the workflow of their coded work, while the reviewers have some comments and suggestions needed to be clarified before it can be published after Minor Revision.

1. The reviewer’s suggestion is avoiding using the specific values for the KGE in this Abstract section. Instead, this section should provide epitome of the entire work in a succinct and clear way.
2. The authors have done a good work in introducing the previous study work and its research gap, and what they need to do to fill this research gap, i.e., develop the coupled streamflow and lake model via the various discharges (e.g., surface, subsurface, groundwater etc.)
3. Material and methods. This section is generally well written and Fig. 2, 3, and 4 are nice figures to illustrate the procedure of the modeling frame well. Regarding the Section 2.5 Validation of streamflow at catchment scale, it is better by providing the range for the quality of Kling-Gupta efficiency (KGE) values. For example, in which ranges stand for model performance is excellent, good, poor etc., and this definition needs some references to support it. Another comment is to define the CVsim and CVobs, which the reviewer considers as Coefficient of Variation.
4. Line 229: ‘…… we assume than lake evaporation ……’ maybe changed to ‘…… we assume that lake evaporation ……’;
5. Line 223 and other places: The authors please make sure that whether 70 or 71 lakes in Sweden are studied. This needs to be consistent throughout the texts.
6. Line 248-249: ‘For all study sites, the KGE exceeded -0.41, indicating that the simulated streamflow provided added value compared to using long-term mean values.’ The reviewer is a little bit confused that a negative value of KGE (e.g., -0.41) means this revision provides added value.
7. In the Results Section. The authors have compared their model with reference results and observed data, respectively. The reviewer considers that would that also necessary to compare the reference results with the observed data. By doing so, the reader could have better understanding that whether the developed model improves its performance or not, compared with the traditional model (i.e., the reference results).
8. The current writing of this part could be improved in a more detailed way. For example, providing some skill metric values that are specified (e.g., various KGE values), so that this work could be better summarized in a more strict way.

The study presents a method of re-scaling gridded water flow data on lake catchments. The method is developed within the framework of ISIMIP, the model intercomparison platform facilitating access to climate scenarios, models, and observational data for model validation. The manuscript is well-structured, clearly written, and addresses an important gap in coupling water flow and lake models on global scales. The proposed method uses a straightforward rescaling algorithm, differentiating between three options---the catchment is smaller than a single grid cell, the catchment is larger than, but the lake is smaller than a grid cell, and the  lake is larger than a single grid cell. The approach has been validated against the long-term outputs of the operational regional hydrological model HYPE applied to 71 Swedish lakes and against a smaller observational dataset, demonstrating satisfactory performance. The results, summarized in two pages and two figures, are clear and concise. The impact on the modeling community can be however limited: while Swedish lakes provide a robust and diverse test case, the extrapolation to global conditions (particularly arid and tropical systems with highly variable evaporation and different hydrological regimes) remains speculative. Still, it is a valuable methodological contribution, with openly available code and datasets, which ensures reproducibility, and an initial step towards coupling lake and water flow modeling in climate models. 

Specific comments: 

• The case of Lake Mälaren demonstrates that irregular morphologies can strongly affect scaling performance. The authors might consider providing more concrete recommendations for how to approach such cases practically. 
• Only six lakes are compared against observed streamflow. While this is understandable due to data availability, a short description of the lakes representativity, in terms of lake size, geographical location, hydrological regime, would strengthen confidence.
• The validation method assumes negligible contribution of lake evaporation/precipitation  compared to inflow/outflow budget. The assumption would be justified if supported by characteristic values of monthly/annual evaporation from the six lakes.