Continental-Scale Coupled Groundwater-Surface-Water Modelling
Abstract
Groundwater accounts for almost one third of the world's fresh water. Lakes and wetlands account for an additional 0.25%, but are intimately linked with groundwater systems. Both modern and past lake levels record changes in regional groundwater tables. The evolution of water table depth through time records changes in the total terrestrial water storage in response to changing climate and topography. To study terrestrial water balance through the past and present, we develop and implement a coupled groundwater-surface-water model that can rapidly compute water-table fluctuations on a continental scale over time scales from years to thousands of years.
We model groundwater-table evolution following Reinfelder et al. (2013), using Darcy's Law with a finite-difference approach in a single layer of vertically-integrated hydraulic conductivity. Surface-water movement and storage are rapidly computed by constructing a map of flow directions and a hierarchy of all depressions in the landscape. Surface water is redistributed following a "fill-merge-spill" methodology: runoff flows into a local depression until it overfills, spilling over and merging with a neighbour. Surface water eventually infiltrates and becomes groundwater, reaches the ocean, or is retained in a depression to form a lake. When using this method over long time periods (from the Last Glacial Maximum, 21,000 years ago, to the present day), one way to validate the results is by comparison to strandlines that indicate past lake levels. Since the size of a lake is directly influenced by the wetness of the climate inputs used, these results can be used to correct the outputs of general circulation models, and thus improve predictions of the past climate whose influence is still felt in present-day lakes, river systems, and water tables.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H53B..02W
- Keywords:
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- 1816 Estimation and forecasting;
- HYDROLOGY;
- 1839 Hydrologic scaling;
- HYDROLOGY;
- 1843 Land/atmosphere interactions;
- HYDROLOGY;
- 1847 Modeling;
- HYDROLOGY