The hydrosphere is made up of a number of components, including groundwater, oceans, shelf seas, estuaries, rivers, sea ice. The transport processes taking place in these domains vary vastly from domain to domain and are characterised by a wide range of space and time scales. These components also interact with each other at a number of space and time scales. Understanding and quantifying this complexity necessitates models that simultaneously deal with most, if not all, of the components of the hydrospheric system.
Numerical models of each of the components of the hydrosphere already exist. However, an integrated model of the whole hydrosphere has yet to developed. Building such a model is a daunting task, requiring the development of multi-scale/physics simulation tools.
Numerical methods for dealing with multi-scale problems are developing rapidly. Unstructured meshes offer an almost infinite geometrical flexibility, allowing the space resolution to be increased when and where necessary. In addition, time steppings for dealing with a wide spectrum of timescales while retaining a high order of accuracy have been developed over recent years (e.g. multi-rate schemes).
In the light of the abovementioned progress in numerical methods, various teams over the world have started developing models for simulating in an integrated manner a significant number of components of the hydrosphere. Ours is one of these groups; we are building the Second-generation Louvain-la-Neuve Ice-ocean Model (SLIM2). The latter solves the equations governing geophysical, environmental and groundwater phenomena by means of the (discontinuous Galerkin) finite element method on 1D, 2D or 3D unstructured meshes. To take advantage of state-of-the-art developments, SLIM is also being interfaced with existing tools (often based on radically different numerical methods), such as the widely-used General Ocean Turbulence Model (GOTM).
The current status of SLIM will be presented, as well as developments planned in the near future. It will be seen that space-time mesh adaptivity pays off. Idealised test cases will be reported on, including a well-known three-dimensional ROFI benchmark. Realistic problems will also be dealt with, in particular the application of SLIM to the Great Barrier Reef, Australia. The potential for using SLIM's dynamical core in existing atmospheric models will be briefly considered.