UPDATED ROUTINE SCHEME IN ORCHIDEE

Meeting of the 18 / 02 / 2019

Present: Agnes Ducharne, Yann Meudesoif, Jan Polcher, Thomas Dubos, Catherine Ottle, Pascal Maugis, Matt Macgrath, Korato Hamada, Philippe Peylin

Excused: Josefine Ghattas, Xudong Zhou

A/ IMPROVE ROUTINE (Supermesh) TowardsParallelRouting.pdf​: Presentation by Jan P. of a new routing scheme based on the description of the Hydrological units (HTUs) within the grid of ORCHIDEE. Each grid cell of ORCHIDEE may contain several HTUs with the water flowing toward a common 'point'. HTUs may cover several grid cell of ORCHIDEE.

B/ SIMPLE ROUTING: Presentation by Yann M. of the so-called "simple routing" scheme based on the current ORC routing scheme but externalised: the runoff and drainage fluxes calculated on the ORCHIDEE grid are map onto an independant grid representing the basins and their connections. The transport of the flow is done on this new "basin" grid and any return water flux should be interpolated on the ORC grid. This allows flexible parallel implementation.

From the discussion 3 majors directions of work emerge:

• Improving the "simple" scheme of Yann M.: Y.M needs some help to run some tests with a given precipitation field (or directly with a runoff+dranaige flux from an ORC run); This will allow to evaluate the potential of this simple external approach. (Agnes proposed to help).

• Define a common/optimal target for the routing scheme that the ORCHIDEE group would like to have. This could combine the advantages of both Yann and Jan approaches. For that a document should be written to resume the approach and iterate on the best solution (independent grid or embedded in the ORC grid; implementation of floods, ponds, etc...)

• Current works are using a relatively old "basin description" while Jan now has access to a new basin description at 90m (from Dai Yamazaki, based on the MERIT DEM). Jan need some help to work on this new hydrography database to extract the relevant information at a suitable resolution.

Note finally that the current ORCHIDEE routing scheme (used for CMIP6) should be corrected with respect to the transfer time of the water in the different reservoirs (bug that make this transfer time strongly dependent on the grid resolution).

Objectives for an optimal Routing Scheme

To be defined...