In ORCHIDEE the graph of the water routing through rivers was generated on the fly in the main code. These developments are documented in Nguyen-Quang et al. 2018 and integrated in the ORCHIDEE-ROUTING branch.
This solution is not ideal for various reasons :
- It is difficult to parallelize as in ORCHIDEE the domain decomposition does not foresee exchange of halos.
- The routing graph produced in ORCHIDEE could not easily be verified before a simulation is launched.
- We plan evolutions of the routing scheme which will require a large number of extra information (floodplains, dams, adduction networks, ...) and it will be complicated to add them within the full model.
This pre-processor generates the full information needed by ORCHIDEE to route the water to the ocean or return it to evaporative processes. It required the grid of the model and the land/sea mask as well as a detailed description of hydrological surface network. All the rest should be ancillary information.
Furthermore the global hydrological data (HydroSHEDS, MERIT) sets are at such high resolution now, that they cannot be dealt with on one processor alone. It is necessary to parallelize the usage of these data and the construction of the routing graph for ORCHIDEE. This parallelization is more driven by the memory needs than the speed of simulation and thus could be different than in ORCHIDEE itself.
The package also includes a viewer which allows to verify the structure of the graph of HTUs which is generated. It provides pictures like the one below.
The Seine basin on a curvilinear atmospheric grid (in black) is displayed. The HTUs are represented as Voronoi polygons (red) and the elevation of HTUs is colour coded. The main stream of the Seine through the HTU graph is depicted in blue.