Abstract. The growing global demand for heating and cooling challenges decarbonization efforts, which requires a shift to renewable solutions. Inland waters, especially lakes and reservoirs, account for a significant portion of global land heat uptake, offering potential to help meet these demands. When used for heating, the resulting cooled lake could benefit from buffering climate-induced warming. However, existing lake models lack dedicated capabilities to simulate thermal energy extraction limiting the assessment of its environmental impacts on aquatic ecosystems. Here, we present a new thermal use module integrated into the General Lake Model (GLM) framework. The module features: (1) depth-flexible water extraction and injection at static or dynamic elevations; (2) user-defined operational parameters for flow rates, temperature spread, and heat flux; and (3) coupling with the Aquatic Ecodynamics (AED) library, enabling simulations of biogeochemical responses to thermal alterations. Heat transfer calculations are integrated with GLM's existing hydrodynamic and thermodynamic algorithms and maintain energy and mass conservation. We tested the module using a heat-extraction scenario (-2 K) for a drinking water reservoir in Germany with 19 years of monitoring data. The open-source module provides a new tool for both energy and lake management by enabling the evaluation of the thermal and ecological impacts of heat extraction.
Received: 29 Jun 2026 – Discussion started: 21 Jul 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.
The manuscript is an excellent contribution to GMD as it highlights a new module for the popular GLM-AED model that provides scientists and managers with the option to simulate heat extraction from lakes and reservoirs, which, potentially, can be a low emission heating method. I very much enjoyed reading the draft and only offer a couple of minor comments to an overall well-described study.
L33: The link between the sentences seems off. First, you describe how the method is environmentally friendly but is nonetheless a manipulation of the lake regime, with all the associated potential ecological consequences. Then you derive a challenge, which is mostly technical. Wouldn’t the challenge be to derive quantifications on how heat extraction would affect the thermal regime, and for this you are developing these tools and processing workflows?
L52: “model here presented was verified against first principles”
L66-70: These advantages seem very general and fit also well to Simstrat. Maybe you can first describe that GLM is popular (wide spread use) with active development and then that it offers (1) open-source and modularized source code, which is easier to change, plus (2) coupling to AED, and (maybe) (3) its historical research focus on reservoir dynamics, which would be an ideal application for heat extraction?
Figure 1 and lines 80-88: I suggest to rename “open and closed-loop system” to something more akin to extraction and injection in the text? Also I suggest to add additional information to the figure caption.
L116 and below: please standardize the amount of digits, sometimes it’s default: 2 deg C, sometimes default: 2.0 deg C; same in Table 1
L143: Can this cause numerical instabilities under extreme injection scenarios, e.g., because the model fails to create enough layers for mixing afterwards? Is that possible?
L155: Maybe revise to “Assuming that residence time is negligible, the model does not account for any biogeochemical transformations between intake and backflow.”
L186: Unclear to me where point (1) controlled verification is? Aren’t all points related to this one?
L189: The scenarios are later defined sometimes as HP-OFF instead of HP off. Also, HP-on should also be explicitly defined somewhere
L290: Would it be possible to also discuss the energy benefits of heat extraction from lakes? Is this economically feasible? Can your model results quantify this in back-of-the-envelope calculation?
GLM: Thermal Use Module to integrate heat extraction into the General Lake ModelTaynara Fernandes, Matthew Hipsey, Laura Soares, Bertram Boehrer, and Karsten Rinke https://doi.org/10.5281/zenodo.21035097
Lakes store large amounts of heat that could be used to warm nearby buildings, offering a clean alternative to fossil fuels. To explore this, we added a new feature to a widely used lake computer model (GLM) that simulates how taking water out for heating, and returning it afterwards, affects a lake's temperature. Our feature enable scientists and communities energy planners to check how much energy can be drawn while keeping the lake healthy.
Lakes store large amounts of heat that could be used to warm nearby buildings, offering a clean...
The manuscript is an excellent contribution to GMD as it highlights a new module for the popular GLM-AED model that provides scientists and managers with the option to simulate heat extraction from lakes and reservoirs, which, potentially, can be a low emission heating method. I very much enjoyed reading the draft and only offer a couple of minor comments to an overall well-described study.