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High-resolution RCMs can provide climate prediction projection information on regional and local scales in relatively fine detail, which cannot be obtained from lower resolution Global Climate Models (GCMs). This is manifested in more realistic descriptions of small-scale regional climate characteristics including extreme events. Consequently, outputs of such RCMs are important 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.
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.
The term "experiment" in the CDS form distinguishes between three main simulation categories of simulations:
- 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 driven by boundary conditions provided by GCMs. These experiments cover a period for which modern climate observations exist. 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 driven by boundary conditions from GCMs using RCP (Representative Concentration Pathways) forcing scenarios. The scenarios used here are RCP 2.6, 4.5 and 8.5 they provide different pathways of the future climate forcing. The period covered is typically 2006-2100.
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