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 (from 0.1 m/yr to 10 m/yr) and total water inventories expressed as Global Equivalent Layer (from 1 mGEL to 1000 mGEL). 48 Simulations are iterated to reach the steady state. 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.

Figures (16)

• Figure 1: Representation of the water cycle on a conceptual topography with 4 leaf depressions. (a) 3D block represents the water flow from upstream to downstream. The links between the depressions, which represent streams, are symbolized by full blue curves. The sky blue dotted line represents the lake elevation where a depression No.1 can merge with a depression No.2 and create a new depression No.5. The dark blue dotted line represents the lake elevation where the depression No.5 merge with the depression No.3. The merge lines (blue and black dotted lines) are projected on the cross-section (b) of the 3D block diagram. (b) The dashed lines represent the minimum and maximum elevation limits of the depressions. (c) Binary tree of the depression hierarchy. Nodes No.1-4 are leaf depressions and nodes No.5-7 are meta-depressions. The black lines represent the merge into a new depression. The dotted arrows show the link with downstream depression. Adapted from barnesComputingWaterFlow2020.
• Figure 2: Mars topographic map showing the inventory of observed data relating to water flow effects. (a) Digital Elevation Model (DEM) from the Mars Orbiter Laser Altimeter (MOLA) Smith2001MOLANeumann2001MOLA. The shaded relief is generated from the DEM with a sun angle of 45° from horizontal and a sun azimuth of 315°, as measured clockwise from north. The blue lines represent the valley networks hynekUpdatedGlobalMap2010. The white and red dots represent open-basin and closed-basin lakes, respectively goudgeInsightsSurfaceRunoff2016. The orange triangles represent deltas diachilleAncientOceanMars2010d. The magenta and yellow lines represent respectively Arabia perronEvidenceAncientMartian2007 and Deuteronilus IVANOV201749 shorelines. The white squares are zoomed areas on Nirgal Vallis' watershed (b), Jezero' watershed (c) and Gale' watershed (d). The white stars on the zoomed areas indicate the outlets of Nirgal Vallis (b), Jezero Crater (c), and Gale Crater (d).
• Figure 3: (a) 9,777 watersheds of leaf depressions are represented on the zoomed area of the Gale crater watershed (Figure \ref{['obs']}d). Gale crater is localized by the white star. The color bar represents the watershed area $A^w_i$. (b) Example of pre-computed hydrological functions for a random depression ($i=4281753$) localized near to the Gale watershed by the white point (a). Evolution of the lake volume $V^{l}_{i}$ (black line) and the lake area $A^{l}_{i}$ (blue curve) as functions of the lake elevation $Z^{l}_{i}$.
• Figure 4: The three maps represent the initial states tested for a $GEL=100$ m. The water is either distributed homogeneously (a), in the northern lowlands (b), or in the Hellas crater (c). The blue areas show the location of water reservoirs. The plots show the evolution of the $P/E$ ratio over time for different $GEL$: 1 m (d), 10 m (e), 100 m (f), and 1,000 m (g). Solid lines, dashed lines, and dotted-dashed lines represent simulations with homogeneous water distribution (a), distribution in the northern lowlands (b), and in the Hellas crater (c), respectively. Green, orange, blue, and black lines represent simulations with fixed evaporation rates of $10$, $1$, $0.1$, and $0.01\,\text{m\,yr}^{-1}$, respectively.
• Figure 5: Distribution of water reservoirs at steady state for each GEL: 1 m (a, b), 10 m (c, d), 100 m (e, f), 1000 m (g, h). The blue areas represent the proportion of water relative to the total water volume (left y-axis) per degree of latitude (left column) and longitude (right column). The solid black lines show the cumulative relative water volume (right y-axis). The dashed black lines represent the cumulative relative water volume for a conceptual homogeneous distribution of water. The red curves on panels (a) and (b) represent the cumulative distribution of crater density (right y-axis) from Robbins2012.