The Water Table Model (WTM) v2.0.1: Coupled groundwater and dynamic lake modelling

Abstract. Ice-free land comprises 26 % of Earth’s surface and holds liquid waters that delineate ecosystems, affect global geochemical cycling, and modulate sea level. However, we currently lack capacity to simulate and predict these terrestrial water changes over the full range of relevant spatial (watershed to global) and temporal (monthly to millennial) scales. To address this gap in knowledge, we present the Water Table Model (WTM), which comprises coupled components to compute dynamic lake and groundwater levels. The groundwater component solves the 2D horizontal groundwater-flow equation by using non-linear equation solvers in the C++ PETSc library. The dynamic lakes component makes use of the Fill-Spill-Merge (FSM) algorithm to move surface water into lakes, where it may evaporate or affect groundwater flow. To demonstrate the continental scale capabilities of the WTM, we simulate steady-state climate-driven present-day and Last Glacial Maximum (LGM: 21,000 calendar years before present) water table for the North American continent. At the LGM, North America stored 6.0 cm sea-level equivalent (SLE) more water in lakes and groundwater than in the climate-driven present-day scenario. We then advance the simulation transiently from 21–16 ka, in which lake volume remains approximately constant but groundwater storage drops by 4.5 cm SLE due to reduced precipitation. Open-source code for the WTM is available on Github and Zenodo.