| 03 Nov 2025
A Global High-Resolution Hydrological Model to Simulate the Dynamics of Surface Liquid Reservoirs: Application on Mars
Abstract. Surface runoff shapes planetary landscapes, but global hydrological models often lack the resolution and flexibility to simulate dynamic surface water bodies beyond Earth. Recent studies of Mars have revealed abundant geological and mineralogical evidence for past surface water, including valley networks, crater lakes, deltas and possible ocean margins dating from late Noachian to early Hesperian times. These features suggest that early Mars experienced periods allowing liquid water stability, runoff and sediment transport. To investigate where surface water could accumulate and how it may have been redistributed, we developed a global high-resolution (km-scale) surface hydrological model. The model uses a pre-computed hydrological database that maps topographic depressions, their spillover points, hierarchical connections between basins, and lake volume-area-elevation relationships. This database approach greatly accelerates simulations by avoiding repeated geomorphic processing. The model dynamically forms, grows, merges and dries lakes and putative seas without prescribing fixed coastlines, by transferring water volumes between depressions according to their storage capacities and overflow rules. We explore model behavior over the present-day Mars' topography measured by MOLA (Mars Orbiter Laser Altimeter) topography for a range of evaporation rates and total water inventories expressed as Global Equivalent Layer (GEL). Simulations are iterated to steady state under the assumption that precipitation balances evaporation plus overflow. The model outputs the extent and depth of surface water bodies and identifies main drainage pathways using overflow fluxes as runoff indicators. Results show a transition toward a contiguous northern ocean between low (1–10 m) GEL values and increasing concentration of water in northern lowlands and major impact basins at higher GEL. We discuss the model's limitations, including its dependence on topography and the absence of subsurface flows, and propose future improvements. This framework provides a quantitative tool to link preserved geomorphology with plausible past hydrological states. Future work will couple the model with a 3D global climate model into a Planetary Evolution Model (PEM) to study transient water redistribution and climate-hydrology feedbacks.
Comment to the authors:
I want to thank you sincerely for this paper and the remarkable work you have clearly invested in it. It has been both a pleasure and a privilege to read. I hope you will receive my comments in the constructive spirit in which they are offered. My suggestions aim only to help clarify your communication and highlight how strong the underlying research already is.
Color code used in the attached PDF:
Blue: Reference requested or missing.
Yellow: General comment or clarification.
Orange: Suggestion for rephrasing or improving clarity.
Red: Typographical, factual, or formatting error.
Summary of main comments:
Scope clarification – The abstract and introduction would benefit from a clearer definition of whether the paper primarily presents a model-development framework or a planetary reconstruction. This distinction will help readers immediately understand the paper’s main purpose.
Model vs. physics separation – In Section 2 (Model Implementation), clarity could be improved by separating the description of physical processes from their algorithmic implementation. A short explanation of which parameters are physical inputs and which are computational simplifications would help readers follow the logic.
Application and results – The Application on Mars section might gain from presenting the results in a concise table (e.g., steady-state outcomes for each GEL) while keeping the text focused on what the simulations reveal about model performance rather than geological interpretation.
Atmospheric coupling and limitations – It would strengthen the paper to state explicitly which atmospheric conditions are assumed or excluded (e.g., wind, pressure, freezing, or transient storage effects). This ensures readers understand what is inside and outside the model’s current scope.
Conclusion and perspective – The conclusion could stress that this work lays a foundation for future coupling with atmospheric and climatic models rather than claiming to fully reconstruct ancient Martian hydrology. This would underline how valuable and versatile your contribution truly is.