Influence of groundwater recharge projections on climate-driven subsurface warming: insights from numerical modeling

Tsypin, Mikhail; Nguyen, Viet Dung; Cacace, Mauro; Blöcher, Guido; Scheck-Wenderoth, Magdalena; Luijendijk, Elco; Krawczyk, Charlotte

doi:10.5194/egusphere-2025-4335

Preprints

https://doi.org/10.5194/egusphere-2025-4335

Preprints

13 Oct 2025

| 13 Oct 2025

Influence of groundwater recharge projections on climate-driven subsurface warming: insights from numerical modeling

Mikhail Tsypin, Viet Dung Nguyen, Mauro Cacace, Guido Blöcher, Magdalena Scheck-Wenderoth, Elco Luijendijk, and Charlotte Krawczyk

Abstract. Groundwater warming due to rising surface temperatures has been documented in both urban and natural settings. However, the potential for long-term changes in the magnitude and seasonality of groundwater recharge to modulate this warming trend has not yet been systematically investigated. In this study, we integrate a stochastic weather generator, distributed hydrologic modeling, and regional thermo-hydraulic groundwater modeling into a unified workflow and apply it to the area of Brandenburg (northeastern Germany). We conduct numerical simulations to assess changes in the subsurface thermal field between present day and 2100, evaluating two climate change scenarios, and incorporate a spectrum of ensemble-based and discrete recharge projections. Our results demonstrate that, while surface temperature rise is the primary driver of the projected groundwater warming of up to 2.5 °C, groundwater flow is responsible for its regional variability in magnitude and affected depths. Higher hydraulic gradients on topographic highs and increased thickness of the permeable Quaternary unit may allow the warming signal to propagate below 200 m depth, whereas groundwater discharge in the river valleys tends to limit it to <200 m. By the late century, the difference in groundwater temperatures between recharge-reduction and recharge-increase scenarios can reach 0.4 °C. Under the high-emissions pathway, a 20 % recharge reduction, from a mean of 75 to 60 mm a^-1, causes a 2–5 m water level decline, reducing the area of unconfined aquifer subjected to seasonal temperature fluctuations. Model experiments show that even a hypothetical increase in winter recharge does not suffice to counteract the groundwater warming induced by rising surface temperatures. Changes in advection rates are not expected to affect the net climate-driven accumulated heat in the subsurface due to counterbalancing of heat gains and losses between recharge and discharge areas. Nevertheless, long-term reconfiguration of the potentiometric surface may further impact both the annual and long-term thermal state of key aquifers targeted for water supply and shallow geothermal energy utilization.

Received: 11 Sep 2025 – Discussion started: 13 Oct 2025

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Journal article(s) based on this preprint

30 Mar 2026

Influence of groundwater recharge projections on climate-driven subsurface warming: insights from numerical modeling

Mikhail Tsypin, Viet Dung Nguyen, Mauro Cacace, Guido Blöcher, Magdalena Scheck-Wenderoth, Elco Luijendijk, and Charlotte Krawczyk

Hydrol. Earth Syst. Sci., 30, 1647–1673, https://doi.org/10.5194/hess-30-1647-2026,https://doi.org/10.5194/hess-30-1647-2026, 2026

Short summary

Mikhail Tsypin, Viet Dung Nguyen, Mauro Cacace, Guido Blöcher, Magdalena Scheck-Wenderoth, Elco Luijendijk, and Charlotte Krawczyk

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-4335', Anonymous Referee #1, 14 Oct 2025

Tsypin and colleagues have submitted a manuscript on evolving subsurface thermal regimes, with the key novel contribution being the role of changing recharge. They conclude that advection plays a role in general, but that changing advection (e.g. more cold-season recharge) cannot overwhelm the overall pattern of groundwater warming from diffusion. The study is generally well written and interesting.
A few comments, in no particular order:
1. Many times in this manuscript the authors use 'temperature' to refer (I think) to surface air temperature; such examples can often be found when referring to climate data. But in a manuscript focused on groundwater temperature, they should always be clear about where in the earth system domain they are referring to when they mention temperature.
2. The authors miss some quite related studies from the Netherlands on the role of groundwater flux on subsurface warming. For example Bense et al. (10.1029/2019WR026913) show how changes to groundwater flow regimes can be inferred from temperature profiles (a close topic to the present manuscript although this former study did not forecast into the future), and Bense et al. 2017 (10.1002/2017GL076015) showed that recharge influences where the inflection point occurs in evolving temperature profiles (see L542, where I think a conference abstract is cited for this point). Also, Figure 9 of the present study shows deep temperature shifts when the flow regime changes. This was also demonstrated by Bense et al. 2017 (10.1002/ 2017WR021496) who showed that using a linear temperature-depth profile as an initial condition results in deep shifts in temperature with time because that initial condition doesn't have the same groundwater flow regime as the forward modeling (e.g., Taniguchi et al. 1999 solution). Side note: I think the authors could do a better job of explaining that groundwater flow regime shifts are what is driving the temperature changes at depth in some of their results (which could not happen under heat diffusion alone under the timescales considered here).
3. Figure 1b - it is stated that this is a 3D view of the model mesh. However, neither the mesh nor the model parameters are indicated (from what I can see). This is just a geological model (or perhaps geometric model of the model domain). Much is made of the geology in this paper (rightfully so), but I think it would be useful to just indicate the parameters on this model domain (at least k and Ss - or put in a clear table). If a table, the thermal properties for each layer would be useful to list too (in the main text).
4. The recharge modeling is impressive - it might be good to be more explicit that all of these recharge realizations do not translate into equivalent model runs for groundwater temperature. I only figured that out later, but I admit to reading this in a moving car with children yelling in my ear etc. The authors calibrate this to streamflow. How does the model performance compare for just baseflow? That might be more comforting to know, since that is a better indicator of whether the recharge and discharge processes are being captured reasonably.
5. Eq. 1 - units don't work - is Recharge in units of 1/s (like a volume flux per unit volume)?
6. This is a big numerical model domain with many elements. Was this solved with high-performance computing or anything - or just run on a 'regular' computer? My simulations with this many nodes took weeks to run, but that was 10 years ago.
7. Boundary conditions questions: a) is there any vertical hydraulic gradient on the vertical boundary conditions at the sides? b) Does the model allow for exfiltration at the surface if the water table rises too high? c) I'm surprised the surface air temp and ground surface temperature are so similar. Is there no snow here? The mean annual air temp of 9C suggests there would be.
8. Using mesh size for characteristic length for Peclet number is arbitrary (but maybe common) - how do the authors know what the threshold is for this Pe formulation for which advection matters? Later on they present Pe values and use these to highlight the role of advection, but this is not a formulation for which Pe =1 implies that advection = conduction (like say the Bredehoeft and Papadopulos 1965 formulation does - if I remember right). So what is the threshold for when advection matters? Maybe that is hard to say.
9. The recharge change runs in the groundwater model are interesting (see Table 1), but I'm still not clear where some of these came from (esp. the discrete synthetic scenario). I guess at least one is more of a sensitivity run rather than an expected scenario? Also, it would be helpful if Table 1 were more precise about timelines rather than "present" and "late century". What years are the before/after runs here for?
10. Model calibration - consider presenting the RMSE normalized to head range. I think that would do a better job of showing the fit. 6.6 m sounds high, but the head is highly variable, so it is not a bad fit at all.
11. Where do groundwater temp measurements come from for calibration? Case borehole temp profiles? Pumped groundwater with temp recorded? Open boreholes? Large diameter? Are convection or seasonal bias concerns?
12. Figure 7 - it would be interesting to also see changes in discharge presented somehow. The authors talk about changes in recharge (input) and head (storage), but what about output (relevant for some of the reasons groundwater temperature is relevant)
13. L386 "Profile A, located on a glacial plateau, has a shallow seasonal envelope, entirely above the water table, suggesting no advective transfer of the seasonal thermal signal into the saturated zone" - I don't think you have to be saturated for heat advection to matter. It depends on the water flux, not the saturation per se. if you have recharge through the vadose zone, advection can still theoretically matter.
Minor comments
L60-65 - I think the controversy over the role of advection is overstated here. In the Benz et al. study, the authors used a parsimonious approach in a global study and justified this using 2D numerical models of advection and conduction. They basically found that for typical hydrogeological systems and recharge rates, heat advection is not a primary driver of groundwater temperature change. However, they note that is not the case for some basins. Other studies cited here are in steeper topography or with much higher recharge, and so it makes sense that they found that advection mattered.
Figure 11 a - label missing for scale bar?
Conclusions _ 'depth limit of advection overprint' sounds a bit jargony for the conclusions
In general, these comments are all easy to address I think, and I look forward to seeing this article published.

Citation: https://doi.org/10.5194/egusphere-2025-4335-RC1
- AC1: 'Reply on RC1', Mikhail Tsypin, 23 Nov 2025
  
  Please see the response in the attached PDF.
  
  Citation: https://doi.org/10.5194/egusphere-2025-4335-AC1
RC2:
'Comment on egusphere-2025-4335', Anonymous Referee #2, 10 Nov 2025
I enjoyed reading the manuscript “Influence of groundwater recharge projections on climate-driven subsurface warming: insights from numerical modeling.” The manuscript presents a clear objective, employs a sound methodology to achieve it, and reports results that are well presented and supported by the discussion and conclusions. Most of my comments focus on improving clarity in certain sections.
Line 167: Could you please explain why these seven GCMs were selected? Since many GCMs are available, I am curious whether these models have specific characteristics that make them particularly suitable for this study. Clarifying this would also address the question of why seven—why not five, ten, or the full ensemble?

For completeness, could you report the area of the model domain? The mesh spans 170 × 150 km, but (as I understand it) the numerical model only simulates part of that rectangle. Are some cells within the bounding rectangle not active? A brief clarification would help.

It would be helpful to include a short paragraph or a few sentences describing the computational cost of the simulations and the computing resources used (e.g., HPC system, number of cores, total runtime).

Line 219: Why were thermal and hydraulic parameters calibrated for only two layers? A short justification would improve clarity.

Line 227: What proportion (in percentage) of the model’s lateral boundaries coincide with rivers?

Some darker points appear in Figure 5a. Do these points represent a specific subset of observations, or are they a rendering artifact? Additionally, could you add a measure of bias between modeled and observed heads and temperatures?

In Figure 6 why were these three wells chosen? Would it not be more informative to select wells from three distinct regions with different expected drawdown responses (Fig. 7a)?

Line 386: The text states that Profile A has a shallow seasonal envelope entirely above the water table, implying no advective transfer of the seasonal signal into the saturated zone. Isn’t this also the case for Profile D?

Section 6.1 is clearly written, and Figure 13 is well designed. However, I’m a bit confused: GD3 is described as an area where “the Rupelian is locally eroded, allowing direct hydraulic connection between Quaternary aquifers and deeper formations”. In Figure 13, the region labeled GD3 appears to still contain Rupelian clay (gray unit), which does not reflect such a direct connection. Could you clarify this?

Line 517: The sentence “The groundwater system is … reversible” may cause confusion. It is clear that your model does not simulate mechanical deformation of the subsurface (and this is okay), yet changes in groundwater storage can lead to changes in hydraulic properties, which may be irreversible depending on geomechanical conditions (Galloway & Burbey, 2011, not my paper, just a reference). I recommend clarifying the assumptions under which the groundwater system is considered reversible in your simulations or rephrasing the sentence to avoid misunderstanding.

Reference:

Galloway, D. L., & Burbey, T. J. (2011). Regional land subsidence accompanying groundwater extraction. Hydrogeology Journal, 19(8), 1459–1486.
Citation: https://doi.org/10.5194/egusphere-2025-4335-RC2
- AC2: 'Reply on RC2', Mikhail Tsypin, 23 Nov 2025
  
  Please see the response in the attached PDF.
  
  Citation: https://doi.org/10.5194/egusphere-2025-4335-AC2
RC3:
'Comment on egusphere-2025-4335', Anonymous Referee #3, 04 Dec 2025
The study by Tsypin et al. aims to quantify future groundwater warming under various climate change scenarios. Its key novelty lies in the explicit consideration of heat advection by groundwater flow, an aspect often overlooked in previous research.
The manuscript is well written and presents a compelling approach. Several comments should be addressed to further strengthen its impact.
General:
It would be beneficial for the reader to make titles of different chapters more detailed.

Figures and legends need more clarity.

Specific comments:
L57 Regarding the impact of GW dynamic on subsurface temperatures, you may also check Klepikova et al., ERL, 2025.
L67 As for the impact of advection on temperature profiles, a review by Kurylyk, 2018 should be cited.
L104 “representative of EU geology” sounds weird.
Fig.1 please provide scale reference on all subfigures.
Section 3: In order to improve the clarity I believe that general conceptual models should be described first.
L167-168 The main difference in between these scenarios should be already mentioned here.
L254 D of fluid?
Figure 3. Expand and detail the legend.
Figure 4. The clarity of this figure could be improved as well.
L343 Could you tell more about the T data (depth/profile or point?/range/precision)?
L370 Please explain “teleconnections”.
Figure 13. It is not really clear what do you want to highlight by horizontal arrows.
L535 This is confusing as the depth of penetration should be regulated by the GW flow rate and thermal properties of rocks.
L541-544 Rephrase this sentence to make it clearer (i.e. what is meant by “this response”?)
L544 differentiation of what?
L645 for which depth?
Citation: https://doi.org/10.5194/egusphere-2025-4335-RC3
- AC3: 'Reply on RC3', Mikhail Tsypin, 26 Dec 2025
  
  Please see the response in the attached PDF.
  
  Citation: https://doi.org/10.5194/egusphere-2025-4335-AC3

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-4335', Anonymous Referee #1, 14 Oct 2025

Tsypin and colleagues have submitted a manuscript on evolving subsurface thermal regimes, with the key novel contribution being the role of changing recharge. They conclude that advection plays a role in general, but that changing advection (e.g. more cold-season recharge) cannot overwhelm the overall pattern of groundwater warming from diffusion. The study is generally well written and interesting.
A few comments, in no particular order:
1. Many times in this manuscript the authors use 'temperature' to refer (I think) to surface air temperature; such examples can often be found when referring to climate data. But in a manuscript focused on groundwater temperature, they should always be clear about where in the earth system domain they are referring to when they mention temperature.
2. The authors miss some quite related studies from the Netherlands on the role of groundwater flux on subsurface warming. For example Bense et al. (10.1029/2019WR026913) show how changes to groundwater flow regimes can be inferred from temperature profiles (a close topic to the present manuscript although this former study did not forecast into the future), and Bense et al. 2017 (10.1002/2017GL076015) showed that recharge influences where the inflection point occurs in evolving temperature profiles (see L542, where I think a conference abstract is cited for this point). Also, Figure 9 of the present study shows deep temperature shifts when the flow regime changes. This was also demonstrated by Bense et al. 2017 (10.1002/ 2017WR021496) who showed that using a linear temperature-depth profile as an initial condition results in deep shifts in temperature with time because that initial condition doesn't have the same groundwater flow regime as the forward modeling (e.g., Taniguchi et al. 1999 solution). Side note: I think the authors could do a better job of explaining that groundwater flow regime shifts are what is driving the temperature changes at depth in some of their results (which could not happen under heat diffusion alone under the timescales considered here).
3. Figure 1b - it is stated that this is a 3D view of the model mesh. However, neither the mesh nor the model parameters are indicated (from what I can see). This is just a geological model (or perhaps geometric model of the model domain). Much is made of the geology in this paper (rightfully so), but I think it would be useful to just indicate the parameters on this model domain (at least k and Ss - or put in a clear table). If a table, the thermal properties for each layer would be useful to list too (in the main text).
4. The recharge modeling is impressive - it might be good to be more explicit that all of these recharge realizations do not translate into equivalent model runs for groundwater temperature. I only figured that out later, but I admit to reading this in a moving car with children yelling in my ear etc. The authors calibrate this to streamflow. How does the model performance compare for just baseflow? That might be more comforting to know, since that is a better indicator of whether the recharge and discharge processes are being captured reasonably.
5. Eq. 1 - units don't work - is Recharge in units of 1/s (like a volume flux per unit volume)?
6. This is a big numerical model domain with many elements. Was this solved with high-performance computing or anything - or just run on a 'regular' computer? My simulations with this many nodes took weeks to run, but that was 10 years ago.
7. Boundary conditions questions: a) is there any vertical hydraulic gradient on the vertical boundary conditions at the sides? b) Does the model allow for exfiltration at the surface if the water table rises too high? c) I'm surprised the surface air temp and ground surface temperature are so similar. Is there no snow here? The mean annual air temp of 9C suggests there would be.
8. Using mesh size for characteristic length for Peclet number is arbitrary (but maybe common) - how do the authors know what the threshold is for this Pe formulation for which advection matters? Later on they present Pe values and use these to highlight the role of advection, but this is not a formulation for which Pe =1 implies that advection = conduction (like say the Bredehoeft and Papadopulos 1965 formulation does - if I remember right). So what is the threshold for when advection matters? Maybe that is hard to say.
9. The recharge change runs in the groundwater model are interesting (see Table 1), but I'm still not clear where some of these came from (esp. the discrete synthetic scenario). I guess at least one is more of a sensitivity run rather than an expected scenario? Also, it would be helpful if Table 1 were more precise about timelines rather than "present" and "late century". What years are the before/after runs here for?
10. Model calibration - consider presenting the RMSE normalized to head range. I think that would do a better job of showing the fit. 6.6 m sounds high, but the head is highly variable, so it is not a bad fit at all.
11. Where do groundwater temp measurements come from for calibration? Case borehole temp profiles? Pumped groundwater with temp recorded? Open boreholes? Large diameter? Are convection or seasonal bias concerns?
12. Figure 7 - it would be interesting to also see changes in discharge presented somehow. The authors talk about changes in recharge (input) and head (storage), but what about output (relevant for some of the reasons groundwater temperature is relevant)
13. L386 "Profile A, located on a glacial plateau, has a shallow seasonal envelope, entirely above the water table, suggesting no advective transfer of the seasonal thermal signal into the saturated zone" - I don't think you have to be saturated for heat advection to matter. It depends on the water flux, not the saturation per se. if you have recharge through the vadose zone, advection can still theoretically matter.
Minor comments
L60-65 - I think the controversy over the role of advection is overstated here. In the Benz et al. study, the authors used a parsimonious approach in a global study and justified this using 2D numerical models of advection and conduction. They basically found that for typical hydrogeological systems and recharge rates, heat advection is not a primary driver of groundwater temperature change. However, they note that is not the case for some basins. Other studies cited here are in steeper topography or with much higher recharge, and so it makes sense that they found that advection mattered.
Figure 11 a - label missing for scale bar?
Conclusions _ 'depth limit of advection overprint' sounds a bit jargony for the conclusions
In general, these comments are all easy to address I think, and I look forward to seeing this article published.

Citation: https://doi.org/10.5194/egusphere-2025-4335-RC1
- AC1: 'Reply on RC1', Mikhail Tsypin, 23 Nov 2025
  
  Please see the response in the attached PDF.
  
  Citation: https://doi.org/10.5194/egusphere-2025-4335-AC1
RC2:
'Comment on egusphere-2025-4335', Anonymous Referee #2, 10 Nov 2025
I enjoyed reading the manuscript “Influence of groundwater recharge projections on climate-driven subsurface warming: insights from numerical modeling.” The manuscript presents a clear objective, employs a sound methodology to achieve it, and reports results that are well presented and supported by the discussion and conclusions. Most of my comments focus on improving clarity in certain sections.
Line 167: Could you please explain why these seven GCMs were selected? Since many GCMs are available, I am curious whether these models have specific characteristics that make them particularly suitable for this study. Clarifying this would also address the question of why seven—why not five, ten, or the full ensemble?

For completeness, could you report the area of the model domain? The mesh spans 170 × 150 km, but (as I understand it) the numerical model only simulates part of that rectangle. Are some cells within the bounding rectangle not active? A brief clarification would help.

It would be helpful to include a short paragraph or a few sentences describing the computational cost of the simulations and the computing resources used (e.g., HPC system, number of cores, total runtime).

Line 219: Why were thermal and hydraulic parameters calibrated for only two layers? A short justification would improve clarity.

Line 227: What proportion (in percentage) of the model’s lateral boundaries coincide with rivers?

Some darker points appear in Figure 5a. Do these points represent a specific subset of observations, or are they a rendering artifact? Additionally, could you add a measure of bias between modeled and observed heads and temperatures?

In Figure 6 why were these three wells chosen? Would it not be more informative to select wells from three distinct regions with different expected drawdown responses (Fig. 7a)?

Line 386: The text states that Profile A has a shallow seasonal envelope entirely above the water table, implying no advective transfer of the seasonal signal into the saturated zone. Isn’t this also the case for Profile D?

Section 6.1 is clearly written, and Figure 13 is well designed. However, I’m a bit confused: GD3 is described as an area where “the Rupelian is locally eroded, allowing direct hydraulic connection between Quaternary aquifers and deeper formations”. In Figure 13, the region labeled GD3 appears to still contain Rupelian clay (gray unit), which does not reflect such a direct connection. Could you clarify this?

Line 517: The sentence “The groundwater system is … reversible” may cause confusion. It is clear that your model does not simulate mechanical deformation of the subsurface (and this is okay), yet changes in groundwater storage can lead to changes in hydraulic properties, which may be irreversible depending on geomechanical conditions (Galloway & Burbey, 2011, not my paper, just a reference). I recommend clarifying the assumptions under which the groundwater system is considered reversible in your simulations or rephrasing the sentence to avoid misunderstanding.

Reference:

Galloway, D. L., & Burbey, T. J. (2011). Regional land subsidence accompanying groundwater extraction. Hydrogeology Journal, 19(8), 1459–1486.
Citation: https://doi.org/10.5194/egusphere-2025-4335-RC2
- AC2: 'Reply on RC2', Mikhail Tsypin, 23 Nov 2025
  
  Please see the response in the attached PDF.
  
  Citation: https://doi.org/10.5194/egusphere-2025-4335-AC2
RC3:
'Comment on egusphere-2025-4335', Anonymous Referee #3, 04 Dec 2025
The study by Tsypin et al. aims to quantify future groundwater warming under various climate change scenarios. Its key novelty lies in the explicit consideration of heat advection by groundwater flow, an aspect often overlooked in previous research.
The manuscript is well written and presents a compelling approach. Several comments should be addressed to further strengthen its impact.
General:
It would be beneficial for the reader to make titles of different chapters more detailed.

Figures and legends need more clarity.

Specific comments:
L57 Regarding the impact of GW dynamic on subsurface temperatures, you may also check Klepikova et al., ERL, 2025.
L67 As for the impact of advection on temperature profiles, a review by Kurylyk, 2018 should be cited.
L104 “representative of EU geology” sounds weird.
Fig.1 please provide scale reference on all subfigures.
Section 3: In order to improve the clarity I believe that general conceptual models should be described first.
L167-168 The main difference in between these scenarios should be already mentioned here.
L254 D of fluid?
Figure 3. Expand and detail the legend.
Figure 4. The clarity of this figure could be improved as well.
L343 Could you tell more about the T data (depth/profile or point?/range/precision)?
L370 Please explain “teleconnections”.
Figure 13. It is not really clear what do you want to highlight by horizontal arrows.
L535 This is confusing as the depth of penetration should be regulated by the GW flow rate and thermal properties of rocks.
L541-544 Rephrase this sentence to make it clearer (i.e. what is meant by “this response”?)
L544 differentiation of what?
L645 for which depth?
Citation: https://doi.org/10.5194/egusphere-2025-4335-RC3
- AC3: 'Reply on RC3', Mikhail Tsypin, 26 Dec 2025
  
  Please see the response in the attached PDF.
  
  Citation: https://doi.org/10.5194/egusphere-2025-4335-AC3

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

ED: Publish subject to minor revisions (further review by editor) (05 Jan 2026) by Gabriel Rau

Thank you for submitting your detailed and thoughtful responses to the reviewers’ comments. After careful consideration of the reviews and your point-by-point replies, I am pleased to inform you that the manuscript requires minor to moderate revisions before it can be accepted for publication in HESS.

Overall, your responses to the reviewers are constructive, transparent, and technically well reasoned. The reviewers’ comments can be addressed to a high standard through clearer framing, improved figures and tables, additional references, and explicit clarification of assumptions, scope, and limitations. In several instances, the suggested revisions go beyond editorial polish and materially improve the manuscript’s clarity and interpretability.

Where you chose not to fully adopt specific reviewer suggestions (e.g. retention of the overall model structure, scope limitations on discharge analysis, or withdrawal rather than reinterpretation of Péclet number diagnostics), your justifications are clear, defensible, and appropriate given the study objectives and data constraints. These decisions do not undermine the central conclusions and, in some cases, strengthen the manuscript by avoiding over-interpretation.

Beyond the reviewers comments, please ensure that:

- All promised clarifications, rewordings, and added references are consistently implemented throughout the revised manuscript.

- Figure labels, captions, and in-text references are fully aligned following the revisions.

- Limitations discussed in the responses are clearly reflected in the Discussion and Conclusions, without diluting the main findings.

I appreciate the care and professionalism with which you have engaged in the review process. I look forward to receiving the revised manuscript as well as final responses to the reviewers and anticipate that it will make a strong and valuable contribution to the literature on climate-driven groundwater thermal dynamics.

Hide

AR by Mikhail Tsypin on behalf of the Authors (15 Jan 2026) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (19 Jan 2026) by Gabriel Rau

The authors have done an incredible job at revising the manuscript according to the reviewers' recommendations. However, I do have a few points that require addressing beyond this revision before I can accept the manuscript for publication in HESS. Please submit a response to each of these points.

Minor aspects to be addressed:

- Revise Section 5.3 (page 15, lines ~416–420) and the opening of Section 6.3 (page 20–21, lines ~555–565) to clarify the role of advection. Where the text refers to a “dominance of advective heat transport” or similar phrasing, explicitly qualify that advection dominates local and spatial variability of groundwater temperatures within the meteoric circulation zone, while diffusion controls basin-scale and long-term heat accumulation. Introduce this clarification at first occurrence and ensure consistent wording in subsequent references.

- In Section 6.2 (page 19–20, lines ~520–550) and/or the Conclusions (page 23, lines ~655–670), explicitly restate that conclusions regarding discharge-related buffering of subsurface warming are conditional on the boundary condition choice, specifically the representation of rivers as time-invariant Type III (regulated stage) boundaries. Ensure it is clear that these findings may not directly apply to systems with freely adjusting river stages.

- In Section 6.3, Recharge seasonality discussion (page 21, lines ~565–575), add a short explanatory sentence clarifying that increased total or winter-biased recharge does not lead to groundwater cooling because recharge temperatures increase concurrently with rising surface temperatures under climate change. Make this causal linkage explicit to avoid counter-intuitive interpretation.

- In the Discussion or Conclusions (page 22–23, lines ~610–675), briefly reiterate the limitation already stated in Section 5.1 (page 12, lines ~365–368) by reminding readers that projected transient groundwater temperature changes are model-based and not directly validated against long-term observational temperature time series. Adjust phrasing where necessary to ensure the strength of conclusions remains aligned with this limitation.

- Where later sections refer broadly to “surface warming” or “surface temperature,” briefly remind the reader at first re-occurrence in the Discussion that this forcing is implemented via near-surface air temperature used as a proxy for land surface temperature, as defined in Section 3.3. This will ensure consistent interpretation of the boundary condition throughout the paper.

- Standardise terminology related to thermal signal modification by preferentially using one term for each process. For example, use “attenuation” or “damping” when referring to thermal signals and reserve “buffering” for hydrological or discharge-related effects. Apply this consistently in Sections 5.3, 6.2, and 6.3 to reduce semantic ambiguity.

- Ensure that statements describing groundwater temperature changes in the Results and Discussion consistently reflect their model-based nature. Where phrasing currently implies direct observation (e.g. “groundwater warming reaches X °C”), adjust wording to “modelled” or “projected” groundwater warming, in line with the calibration and validation limitations described in Section 5.1.

- When discussing longer-term groundwater system reorganisation in Section 6.2, explicitly restate that hydraulic and thermal properties are assumed time-invariant in the simulations. Clarify that any discussion of basin-scale reorganisation refers to changes in flow patterns driven by boundary conditions rather than evolving subsurface properties.

- In Section 6.4, slightly strengthen the transition from regional-scale modelling results to installation-scale geothermal implications by explicitly noting that statements about GSHP or ATES performance are indicative and conceptual, rather than site-specific predictions. This will align scale-dependent interpretations more clearly with the modelling framework.

- Finally, refine the final paragraph of the Conclusions (page 23, lines ~670–680) to explicitly qualify the transferability of the results. I suspect that the strongest inferences apply to temperate, recharge-controlled, low-relief hydrogeological settings comparable to Brandenburg, and that extrapolation beyond such settings should be made with caution. Ensure this qualifier aligns with the modelling assumptions without weakening the main conclusions.

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AR by Mikhail Tsypin on behalf of the Authors (29 Jan 2026) Author's response Author's tracked changes Manuscript

ED: Publish as is (01 Feb 2026) by Gabriel Rau

AR by Mikhail Tsypin on behalf of the Authors (16 Feb 2026) Manuscript

Post-review adjustments

AA – Author's adjustment | EA – Editor approval

AA by Mikhail Tsypin on behalf of the Authors (25 Mar 2026) Author's adjustment Manuscript

EA: Adjustments approved (26 Mar 2026) by Gabriel Rau

Journal article(s) based on this preprint

30 Mar 2026

Influence of groundwater recharge projections on climate-driven subsurface warming: insights from numerical modeling

Mikhail Tsypin, Viet Dung Nguyen, Mauro Cacace, Guido Blöcher, Magdalena Scheck-Wenderoth, Elco Luijendijk, and Charlotte Krawczyk

Hydrol. Earth Syst. Sci., 30, 1647–1673, https://doi.org/10.5194/hess-30-1647-2026,https://doi.org/10.5194/hess-30-1647-2026, 2026

Short summary

Mikhail Tsypin, Viet Dung Nguyen, Mauro Cacace, Guido Blöcher, Magdalena Scheck-Wenderoth, Elco Luijendijk, and Charlotte Krawczyk

Data sets

Long-term synthetic weather data, groundwater recharge and a thermo-hydraulic groundwater model for Berlin-Brandenburg (1955-2100) M. Tsypin et al. https://doi.org/10.5880/GFZ.CUEG.2025.001

Model code and software

mesoscale Hydrologic Model (mHM) source code L. Samaniego et al. https://doi.org/10.5281/zenodo.4575390

Mikhail Tsypin, Viet Dung Nguyen, Mauro Cacace, Guido Blöcher, Magdalena Scheck-Wenderoth, Elco Luijendijk, and Charlotte Krawczyk

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Shallow groundwater temperatures are increasing as a consequence of global warming. At the same time, climate models project substantial changes in future groundwater recharge, with impacts on groundwater levels. We investigated the combined effects of these two processes. Our modeling results suggest that decreased annual recharge or increased cold recharge in winter can locally slow groundwater warming, but not sufficiently to stop or reverse the overall warming trend.


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