Update of the EUR balance ensemble matrix

[jesusff]

This is a proposal raised by @csteger during the recent EURO-CORDEX GA 2026 to include CCLM in the balanced matrix experiment. The matrix would look like this:

All other simulations remain the same, just the CCLM6-0-1 ones were added. The only problem I see is that the CCLM driving GCMs are a subset of those for ICON. On the other hand, the MPI-ESM>ICON simulation is contributing to unbalance the ensemble, by having both the GCM and RCM an excess in the matrix.

The building rule was to have at least 3 GCMs per RCM and at least 4 RCMs per GCM. This minimum (3,4) cannot be achieved, but this MPI>ICON simulation is enlarging unnecessarily the matrix. By dropping it, MPI would have 4 nested RCMs, ICON is nested to 3 GCMs and CCLM and ICON would have two independent sets of driving GCMs. I understand that this MPI>ICON simulation is a flagship simulation for the UDAG project, so let me know what do you think.

On the other hand, and in principle unrelated to this, the CNRM-ESM2-1 GCM is at risk of not having the minimum number (4) of RCMs nested into it. RegCM5 simulations at CUNI are still planned (@micval could you provide an update?). The MPI>ICON simulation could be replaced by the CNRM>ICON one to make sure we meet the balance design. In this case, the HCLIM set (@gnikulin ) would be a subset of those driving ICON.

@guillaumeevin @sam-somot @stefan-sobolowski what do you think?

[guillaumeevin]

In my view, it is already a solid effort to have followed these recommendations, and the matrix design already seems much more balanced to me than in the previous exercises. Additional simulations seem like a bonus. I do not think the matrix can become unbalanced because of additional simulations as there is already a balanced baseline set that allows for robust comparisons between simulations. That said, I think replacing MPI>ICON by CRNM>ICON is an excellent suggestion.