A high-resolution hydrological model at planetary scale : conceptual study of the distribution and evolution of water reservoirs on early Mars.

In past decades, the study of Mars revealed geological and geochemical indicators regarding the past presence of valley networks, lakes and even possibly oceans, particularly at the end of the Noachian and the beginning of the Hesperian epochs. These indicators suggest a potentially long stable period during which early Mars could have had a climate warm and wet enough to allow the presence of surface liquid water and precipitation.

To understand the evolution of the planet's hydrological cycle, we developed a new high-resolution surface hydrological model to constrain hydrological processes. The resolution of our model is obtained from the data of MOLA (Mars Orbiter Laser Altimeter) topographic map (1/128°). Our approach is based on the creation of a global hydrological database to define the location of topographic depressions and their spillover flow point, the hydrological connection between watersheds, and a relationship between elevation, volume, and area of generated lakes. This database significantly accelerates the computation speed of the hydrological model. The hydrological model can simulate the drying up or formation of lakes and oceans based on various parameters. In this conceptual study, we primarily explore the variability in the location of precipitation and the amount of available water on the surface of Mars, in Global Equivalent water Layer (GEL) units.

The hydrological model performs detailed simulations by transferring water between watersheds according to their water storage capacity. Simulations are run in steady state, to ensure that inflow (precipitation) and outflow (evaporation and overflow) are equal. The model provides the location and extent of lakes and oceans depending on the amount and location of precipitation. Lake overflow rates are used as markers to identify runoff. To align with one of our plausible conceptual models, we use the relative climate aridity indicator (X-ratio) to position our study in relation to previous studies and highlight the contribution of this new model. Simulation results are compared with geological and geomorphological observations such as opened and closed lakes, deltas, and valley networks.

The next steps in our work aim to enhance the robustness of our hydrological model by integrating it into a global climate model (GCM) and a planetary evolution model (PEM). This connection will provide a better understanding of the interactions between Mars' hydrological regime and its global climate. We also plan to add subsurface/groundwater flows to our model, providing a perspective on the distribution and dynamics of water under the Martian surface.