This catalogue entry provides daily and monthly Regional Climate Model (RCM) data on single levels from a number of experiments, models, members and time periods computed over Europe and in the framework of the Coordinated Regional Climate Downscaling Experiment (CORDEX). The term "single levels" is used to express that the variables are computed at one vertical level which can be surface (or a level close to the surface) or a dedicated pressure level in the atmosphere. Multiple vertical levels are excluded from this catalogue entry.

High-resolution RCMs can provide climate change information on regional and local scales in relatively fine detail, which cannot be obtained from coarse scale Global Climate Models (GCMs). This is manifested in better description of small-scale regional climate characteristics and also in more accurate representation of extreme events. Consequently, outputs of such RCMs are indispensable in supporting regional and local climate impact studies and adaptation decisions. RCMs are not independent from the GCMs, since the GCMs provide lateral and lower boundary conditions to the regional models. In that sense RCMs can be viewed as magnifying glasses of the GCMs.

The CORDEX experiments consist of RCM simulations representing different future socio-economic scenarios (forcings), different combinations of GCMs and RCMs and different ensemble members of the same GCM-RCM combinations. This experiment design through the ensemble members allows for studies addressing questions related to the key uncertainties in future climate change. These uncertainties come from differences in the scenarios of future socio-economic development, the imperfection of regional and global models used and the internal (natural) variability of the climate system. This experiment design allows for studies addressing questions related to the key uncertainties in future climate change:

• what will future climate forcing be?
• what will be the response of the climate system to changes in forcing?
• what is the uncertainty related to natural variability of the climate system?

The term "experiment" in the CDS form refers to three main categories:

• Evaluation: CORDEX experiment driven by ECMWF ERA-Interim reanalysis for a past period. These experiments can be used to evaluate the quality of the RCMs using perfect boundary conditions as provided by a reanalysis system. The period covered is typically 1980-2010;
• Historical: CORDEX experiment which covers a period for which modern climate observations exist. Boundary conditions are provided by GCMs. These experiments, that follow the observed changes in climate forcing, show how the RCMs perform for the past climate when forced by GCMs and can be used as a reference period for comparison with scenario runs for the future. The period covered is typically 1950-2005.;
• Scenario (RCP2.6, RCP4.5, RCP8.5): Ensemble of CORDEX climate projection experiments using RCP (Representative Concentration Pathways) forcing scenarios. These scenarios are the RCP 2.6, 4.5 and 8.5 scenarios providing different pathways of the future climate forcing. Boundary conditions are provided by GCMs. The period covered is typically 2006-2100.

In CORDEX, the same experiments were done using different RCMs (labelled as “Regional Climate Model” in the CDS form).

In addition, for each RCM, there is a variety of GCMs, which can be used as lateral boundary conditions. The GCMs used are coming from the CMIP5 (5th phase of the Coupled Model Intercomparison Project) archive. These GCM boundary conditions are labelled as “Global Climate Model” in the form and are also available in the CDS.

Additionally, the uncertainty related to internal variability of the climate system is sampled by running several simulations with the same RCM-GCM combination. On the forms, these are indexed as separate ensemble members (the naming convention for ensemble members is available in the documentation). For each GCM, the same experiment was repeatedly done using slightly different conditions (like initial conditions or different physical parameterisations for instance) producing in that way an ensemble of experiments closely related. More details behind these sequential ensemble numbers will be available in the detailed documentation.

On a general level in the CDS form for the RCM simulations “v” enumerates runs and not model versions. Runs numbers different from “v1” means new simulations relative to the first “v1” one. It might not mean a new version.

1. For the EC-EARTH and HadGEM2-ES forced HIRHAM RCM simulation “v2” is a new simulation where proper GHG concentrations changing with time are used as a contrast to “v1” that erroneously used the constant control level throughout the simulation. Therefore users should use "v2".
2. For NorESM forced HIRAM RCM “v2” run includes also an error in the vertical interpolation when preparing the boundary files also exists. Therefore users should use "v3".
3. For the MOHC-HadGEM2-ES forced RACMO simulation "v2" is a new simulation where a big error in SST-remapping from the HadGEM-grid to the RCM-grid in "v1" was corrected. The erroneous v1-simulation has been unpublished from the ESGF.
4. For the CNRM-CM5 forced runs "v2" is a new simulation replacing the old now with input data taken from pressure levels instead of model levels. The originally provided model level fields from CNRM were wrong.
5. Two MPI-driven scenario runs were rerun in 2016 as there had been problems with a restart file and as there was an error in the snow diagnostics in the original run. The reruns were labelled "v1a".

The data are produced by the participating institutes of the EURO-CORDEX and Med-CORDEX projects.

More details about the product are given in the Documentation section.