Extension 1 - CORDEX Overview

This catalogue entry provides Regional Climate Model (RCM) data on single levels from a number of experiments, models, domains, resolutions, ensemble members, time frequencies and periods computed over several regional domains all over the World in the framework of the Coordinated Regional Climate Downscaling Experiment (CORDEX). The term "single levels" is used to express that the variables are 2D-matrices computed on 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 Regional Climate Models (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 "region" in the CDS form refers to the different regional domains, which are as follows:

• EUR: European domain from 27°N to 72°N and from 22°W to 45°E. The horizontal resolution for this domain is 0.11° x 0.11° (EUR-11).
• NAM: North-American domain from 12°N to 59°N and from 171°W to 24°W. The horizontal resolutions for this domain are 0.22° x 0.22° (NAM-22) and 0.44° x 0.44° (NAM-44).

Additional details on each CORDEX geographical domain are available at https://cordex.org/domains/.

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: 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 is available in the detailed documentation.

All known issues about the CORDEX data are documented through the ES-DOC Errata Service : https://errata.es-doc.org/.

The data are produced by the institutes and modelling centres participating in the different CORDEX domains with partial support from different international and national contributions (including support from COPERNICUS for some of the EURO-CORDEX runs and for helping in the data curation and ESGF archiving process in some domains). 

Recommended search procedure: 

1. Select the CORDEX region of interest
2. Select the spatial resolution of interest
3. Select the CORDEX experiment (e.g., future scenario) of interest
4. Select the required variable(s) for your analysis.
5. Select the required time period (which depends on the experiment).
6. The search interface will adapt the other selection fields according to the available data (e.g., which models provides the variable you aim for, how many ensemble are available, etc.)

MARKDOWN FORMAT for teh overview text

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 Regional Climate Models (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**: 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:

- 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".
- 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".
- 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.
- 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.
- 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.

YAML FORMAT for the Description table

---
description:
data-type: Gridded
file-format: NetCDF4
horizontal-coverage: From 27°N to 72°N and from 22°W to 45°E (grid projection may differ among RCMs)
horizontal-resolution: |
0.11°x0.11° for the European domain

0.22°x0.22° and 0.44°x0.44° for the North American domain

temporal-coverage: 1950-2100 (shorter for some experiments)
temporal-resolution: 3h, 6h, daily, monthly and seasonal
vertical-resolution: Variables are provided at a specific single level for each variable. That level may differ among the variables
update-frequency: Regular quarterly updates
conventions: Climate and Forecast (CF) Metadata Convention v1.6
versions: Latest version of the data is provided.

keywords:
- 'Spatial coverage: Europe'
- 'Variable domain: Atmosphere (surface)'
- 'Variable domain: Atmosphere (upper air)'
- 'Temporal coverage: Future'
- 'Temporal coverage: Past'
- 'Temporal coverage: Present'
- 'Product type: Climate projections'

YAML FORMAT for the variables

variables:

  2m temperature:
    units: 'K'
    description: 'The ambient air temperature. The data represents the mean over the aggregation period at to 2m above the surface.'

  Mean precipitation flux:
    units: 'kg m^-2 s^-1'
    description: 'The deposition of water to the Earth s surface in the form of rain, snow, ice or hail. The precipitation flux is the mass of water per unit area and time. The data represents the mean over the aggregation period.'

  2m relative humidity:

    units: '%'

    description: 'Relative humidity is the percentage ratio of the water vapour mass to the water vapour mass at the saturation point given the temperature at that location. The data represents the mean over the aggregation period at 2m above the surface.'

  2m specific humidity:

    units: 'Dimensionless'

    description: 'Amount of moisture in the air at 2m above the surface divided by the amount of air plus moisture at that location.'

  Surface pressure:

    units: 'Pa'

    description: 'Pressure of air at the lower boundary of the atmosphere.'

Mean sea level pressure:

  units: 'Pa'

  description: 'The air pressure at sea level. In regions where the Earth s surface is above sea level the surface pressure is used to compute the air pressure that would exist at sea level directly below given a constant air temperature from the surface to the sea level point. The data represents the mean over the aggregation period.'

10m Wind Speed:

  units: 'm s^-1'

  description: 'The magnitude of the two-dimensional horizontal air velocity. The data represents the mean over the aggregation period at 10m above the surface.'

Surface solar radiation downwards:

  units: 'W m^-2'

  description: 'The downward shortwave radiative flux of energy per unit area. The data represents the mean over the aggregation period at the surface.'

Surface upwelling shortwave radiation:

  units: 'W m^-2'

  description: 'Short wave radiative flux of energy from the surface per unit area.'

Surface thermal radiation downward:

  units: 'W m^-2'

  description: 'Radiative longwave flux of energy incinding on the surface from the above per unit area.'

Total cloud cover:

  units: 'Dimensionless'

  description: 'Total refers to the whole atmosphere column, as seen from the surface or the top of the atmosphere. Cloud cover refers to fraction of horizontal area occupied by clouds.'

500hPa geopotential:

  units: 'm'

  description: Gravitational potential energy per unit mass normalised by the standard gravity at 500hPa at the same latitude.

850hPa U-component of the wind:

  units: 'm s^-1'

  description: 'Magnitude of the eastward component of the two-dimensional horizontal air velocity at 850hPa.'

850hPa V-component of the wind:

  units: 'm s^-1'

  description: 'Magnitude of the northward component of the two-dimensional horizontal air velocity at 850hPa.'

10m v-component of the wind:

  units: 'm s^-1'

  description: 'The magnitude of the northward component of the wind at 10m above the surface. '

10m u-component of the wind:

  units: 'm s^-1'

  description: 'The magnitude of the eastward component of the wind at 10m above the surface. '

200hPa v-component of the wind:
  units: 'm s^-1'
  description: 'The magnitude of the northward component of the wind at 10m 200hPa. '

200hPa u-component of the wind:
  units: 'm s^-1'
  description: 'The magnitude of the eastward component of the wind at 10m 200hPa. '

Total run-off flux:
  units: 'kg m^-2 s^-1'
  description: 'The mass of surface and sub-surface liquid water per unit area and time, which drains from land.'