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Model data formats and structures

What kind of data do models generally produce?

Regional climate model simulations produce 3-dimensional fields of climate variables like temperature, humidity, wind velocity etc. and in addition 2-dimensional fields of surface precipitation, radiation, etc. ESD, on the other hand, may produce time series for a point (1D), a group of points (2D) or derived quantities such as storm tracks, and follow the format of the observations. ESD can also be gridded like observations to provide 2D data objects. In several portals EURO-CORDEX data are used to explore climate model data and to calculate climate impact indicators. Below some links to websites of interest are listed:

How to download EURO-CORDEX projections?

EURO-CORDEX simulations for Europe have been performed for two different horizontal resolutions:

  • 0.44 degree (EUR-44, ~50 km)
  • 0.11 degree (EUR-11, ~12.5km)

The EURO-CORDEX simulations (EUR-44 and EUR-11) are openly available through the Earth System Grid Federation (ESGF) under the CORDEX project.

Steps towards the data download:

  • Accessing and registering at the ESGF Portal:
    • Access the Earth System Grid Federation (ESGF) Search Portal via
      one of the available data nodes (Select nodes from: *http://www.data.euro-cordex.net*)
    • Look for the hyperlink “Create Account” to be granted an ESGF
      OpenID and corresponding password. This account is needed to be able to download data.
  • Searching for data:
    • After registration, go back to the Search Portal and look for the
      hyperlink allowing to access the CORDEX Data Search (this may differ depending on the portal you chose)
    • You may specify the data you are looking for by ticking the
      respective selection options on the left (e.g. Project: “Cordex”, Domain: “EUR-11”, Variable Long Name: “Air Temperature”, etc.)
    • Clicking on “Search” generates a list with all available data that
      match your specifications.
    • Clicking on the interrogation mark next to the “Search” button
      provides you with additional search information
  • Choosing the desired data:
    • If you are unsure which item from the list you are looking for,
      press “show metadata” below each result of the data search to check for additional information or refine your search criteria.
  • Downloading a certain set of data:
    • By opening “Show Files”, you may access a list of files that
      contains the requested data. Depending on the temporal resolution of the data, this can be several data files.
    • You may either download each of these files individually, by
      clicking on “HTTPServer OPENDAP” located right of the file…
    • ...or you download a shell script by clicking on “WGET Script”,
      which manually downloads all data files if run.
    • The download of multiple files could be easier via 'datacart'
      option. You can create a wget-script over all selected files to download them at once.
  • Data Access Login:
    • Enter your ESGF OpenID and corresponding password to download the
      data

More details on how to access CORDEX data are provided in Data Access section on the CORDEX website (*http://www.cordex.org/index.php?option=com_content&view=article&id=228&Itemid=537*).

A subset of the Euro-CORDEX simulations (both EUR-11 and EUR-44), bias-adjusted by a few different methods, are also openly available on ESGF under the CORDEX-Adjust project (*http://www.cordex.org/index.php?option=com_content&view=article&id=275&Itemid=785*). Currently the bias-adjusted daily data for mean/max/min temperature and precipitation is available. This subset of bias-adjusted Euro-CORDEX simulations is a first step. At moment not all Euro-CORDEX simulations are bias-adjusted but work on expanding and filling the bias-adjusted Euro-CORDEX matrix is ongoing.

How to change netcdf into other formats?

The conversion of NetCDF-data into other formats can be carried out with the Climate Data Operator (CDO), which is available at *https://code.zmaw.de/projects/cdo*. The CDO is a collection of command line operators to manipulate and analyse climate and numerical weather prediction model Data. Supported data formats are GRIB, NetCDF, SERVICE, EXTRA and IEG. There are more than 600 operators available

With this tool, data can be converted into the following data formats: grb, grb2, nc2, nc4, nc4c, srv, ext, ieg.

To convert a NetCDF-file into a GRIB-file:

cdo -f grb copy input_file.nc output_file.grb

Furthermore, there is also an option to write NetCDF-data as a customised table into an ASCII-file. However, a NetCDF-file containing two or three dimensional data may not appropriate to write into an ASCII-file without modifications since the data will be written line by line according grid-cells and timesteps orders. Therefore, it can be helpful to calculate a fieldmean of the data or extract one grid-cell before writing into the ASCII-file first:

To calculate a fieldmean:

cdo fldmean input_file.nc output_file.nc

To extract a longitude/latitude point using the nearest-neighbour mapping:

cdo remapnn,lon=XX/lat=yy input_file.nc output_file.nc

Notice: When you are using single grid-cells from climate model data, it may appropriate to calculate the weighted average of each grid point plus the 8 surrounding points to avoid strange values:

cdo smooth9 input_file.nc output_file.nc

To write data as a customised table into an ASCII-file:

cdo outputtab,name,year,month,day,lon,lat,value input_file.nc >output_file.txt

How to read EURO-CORDEX data into analysis tools?

The free data analysis tool R (*http://cran.r-project.org*) can read netCDF files (CF conventions) and allows a large universe of statistical analysis, tests, and visualisation (e.g. regression and extreme value analysis). There is a wide range of R-packages which can be installed on top of R that have been designed for specific uses and purposes. One such package has been especially designed for general climate data analysis and ESD, and is freely available from a GitHub repository (*http://github.com/metno/esd*). It has also been written to process RCM results.

How to extract a specific region?

There are two proven methods how you can select a region: the software ‘Climate Data Operators’ (CDO) for your downloaded files on your computer or a web-based method (*https://climate4impact.eu*) in order to download data that contain only the region of interest.

Once you have downloaded the EURO-CORDEX simulation (see *How to download EURO-CORDEX projections?*), you can select a region by using the command ‘cdo sellonlatbox’ by giving the longitude and latitude coordinates of the edges of the region of interest. For further information or if you have not installed the software CDO, please follow the introductions of this website:` <https://code.zmaw.de/projects/cdo>`__*https://code.zmaw.de/projects/cdo*.

When you prefer to download data only for a specific region, use this web-based method. Login at` <https://climate4impact.eu/>`__*https://climate4impact.eu* with your ESGF account, go to Account -> Processing, select ‘convert and subset.’ Under ‘select a file’, a window opens where you can access via the ‘search function’ the ESGF data. After choosing your file of interest, select your file for processing by clicking on the ‘basket’-icon. Back in the main window, you can either select a region by specifying the longitude and latitude coordinates of the edges of the region. Or you can select the region with your mouse by changing the size of the box which is presented on the map on the right.

After choosing a file name at the bottom of the page, you can press the ‘Start processing’ button and a file in netcdf format with your selected region will be automatically produced and ready for download.

Examples of EURO-CORDEX data use

In the following, some examples of practical use cases of the EURO-CORDEX data are listed, e.g., national diagnostics on climate change. The list is nonexhaustive and growing with time.

Further Reading

  • Jerez, S.; Tobin, I.; Vautard, R.; Montavez, J. P.; Lopez-Romero, J. M.; Thais, F.; Bartok, B.; Christensen, O. B.; Colette, A.; Deque, M.; Nikulin, G.; Kotlarski, S.; van Meijgaard, E.; Teichmann, C. & Wild, M., 2015: The impact of climate change on photovoltaic power generation in Europe, Nature Communications, 6, *https://doi.org/doi:10.1038/ncomms10014*
  • Tobin, I.; Jerez, S.; Vautard, R.; Thais, F.; van Meijgaard, E.; Prein, A.; Déqué, M.; Kotlarski, S.; Maule, C. F.; Nikulin, G.; Noël, T. & Teichmann, C., 2016: Climate change impacts on the power generation potential of a European mid-century wind farms scenario, Environmental Research Letters, 11, 034013, *https://dx.doi.org/10.1088/1748-9326/11/3/034013*

How to cite the EURO-CORDEX ensemble in publications?

ToDo

Existing Guidelines

  • Mearns, L. O., F. Giorgi, P. Whetton, D. Pabon, M. Hulme, M. Lal, 2003: Guidelines for Use of Climate Scenarios Developed from Regional Climate Model Experiments, Final Version - 10/30/03, DDC of IPCC TGCIA, *www.ipcc-data.org/guidelines/dgm_no1_v1_10-2003.pdf*
  • Wilby, R.L., Charles, S.P., Zorita, E., Timbal, B., Whetton, P., Mearns, L.O., 2004: Guidelines for Use of Climate Scenarios Developed from Statistical Downscaling Methods, *www.ipcc-data.org/guidelines/dgm_no2_v1_09_2004.pdf*
  • World Meteorological Organization, 2011: Guide to Climatological Practices, WMO-No. 100, World Meteorological Organization, Geneva, ISBN 978-92-63-10100-6
  • Bund- Länder- Fachgespräch "Interpretation regionaler Klimamodelldaten", 2014: Leitlinien zur Interpretation regionaler Klimamodelldaten, *http://klimawandel.hlug.de/?id=448*
  • Kreienkamp, F., H. Huebener, C. Linke and A. Spekat (2012): Good practice for the usage of climate model simulation results - a discussion paper. Environmental Systems Research 2012, 1:9, *https://doi.org/10.1186/2193-2697-1-9*