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History of modifications

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Version

Date

Description

1.0

08/12/2021

First version

2.131/03/2022Update to version 22.03
3.027/09/2022Update to version 22.09
4.031/03/2023Update to version 23.03
5.030/09/2023Update to version 23.09
6.031/03/2023Update to version 24.03
7.030/09/2024Update to version 24.09
8.031/03/2025Update to version 25.03


List of datasets covered by this document

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titleClick here to expand the list of datasets covered by this document


Product title

Product type

Version Number

Delivery date

NGCDObservational gridded dataset22.0331/03/2022
NGCDObservational gridded dataset22.0930/09/2022
NGCDObservational gridded dataset23.0331/03/2023
NGCDObservational gridded dataset23.0930/09/2023
NGCDObservational gridded dataset24.0331/03/2024
NGCDObservational gridded dataset24.0930/09/2024
NGCDObservational gridded dataset25.0331/03/2025


Related documents

Reference IDDocument

D1

Anchor
D1
D1

NGCD Algorithm Theoretical Basis Document

D2

Anchor
D2
D2

Climate and Forecast (CF) Conventions and Metadata; http://cfconventions.org

D3

Anchor
D3
D3

R Core Team (2017). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL

https://www.R-project.org/

Acronyms 

Acronym

Definition

CDS

Climate Data Store

MET Norway

The Norwegian Meteorological Institute

FMI

Finnish Meteorological Institute

KNMI

The Royal Netherlands Meteorological Institute

SMHI

The Swedish Meteorological and Hydrological Institute

NGCD

Nordic Gridded Climate Dataset (DOI:https://doi.org/10.24381/cds.e8f4a10c)

NGCD-1

NGCD type 1 datasets

NGCD-2

NGCD type 2 datasets

seNorge

Observational gridded dataset over Norway (senorge.no)

ECA&D

European Climate Assessment & Dataset

TITAN

software for automatic quality control (TITAN and titanlib)

OI

Optimal Interpolation

RMSERoot Mean Squared Error

Main variables

Symbol

Definition

TG

Daily mean temperature (from day before the date in the timestamp at 06 UTC, to date in the timestamp at 06 UTC)

TX

Daily maximum temperature (from day before the date in the timestamp at 18 UTC, to date in the timestamp at 18 UTC)

TN

Daily minimum temperature (from day before the date in the timestamp at 18 UTC, to date in the timestamp at 18 UTC)

RR

Daily precipitation total (from day before the date in the timestamp at 06 UTC, to date in the timestamp at 06 UTC)

Data access information

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table_data_access

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The list of Known issues is available at the following link.

Scope of the document

This document is the user guide for the NGCD observational gridded dataset produced under the service contract C3S2_311 Lot3 (Collection and processing of in situ observations - Access to high-resolution gridded datasets over Europe based on in situ observations) on behalf of Copernicus.

The primary objective of this guide is to assist users in comprehending both the features and potential limitations of the dataset. Furthermore, it aims to provide clear instructions on how to access, read, and effectively utilize the data.

Executive summary

The NGCD is an observational gridded dataset that covers Fennoscandia, encompassing Finland, Norway, and Sweden. It exclusively relies on in-situ observations. The dataset includes the following main variables: daily mean temperature (TG); daily maximum temperature (TX); daily minimum temperature (TN); daily total precipitation (RR).

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For data access, please refer to the provided links in the "Data access information" section. A comprehensive description of NGCD is presented in the "Product information" section. Additionally, Appendix A details the evaluation for ver. 18.03, which is consistent with the methodologies employed for all versions up to ver. 25.03. Lastly, Appendix B showcases examples of file structures.

Product information

Product description

The description of the input data and the methods is available in the NGCD Algorithm Theoretical Basis Document [D1]. As specified in D1, the user must be aware that the NGCD input data are non-homogenized time series.

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Figure 7: Daily minimum temperature (TN): spatial distribution of the observing stations used in the production of NGCD when the observational network consists of a smaller number of stations (“sparse” observational network, top row) and a larger number of stations (“dense” observational network, bottom row) with respect to the the time series of available observations (see Figure 3). The left column shows maps over the domain while the right column shows the elevations of the stations (green dots) as a function of their Northing coordinates. As a reference in the background, the gray dots are the elevations of the cells on the 1 km digital elevation model over Fennoscandia.

Data usage information

File naming convention

The data files are in netCDF-4 format and follow the CF-standards, see D2 in Section Related Documents.

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ii) While there's a mention of a version, signaling the methodology deployed in data production, the source of these observations diverges from the historical archive of the corresponding version.

Data format

The key fields provided in this product are as given in Table 1.

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Table 1: Key data fields in the output files.

Variable Name

Description

lon

longitudes of the grid points

lat

latitudes of the grid points

projection_laea

specification of the coordinate reference system

time_bounds

time bounds of the aggregated variable

TG / TX / TN / RR

daily variable in the file

The provided data is single-layered, situated near the surface, and gridded on a regular grid covering Finland, Norway, and Sweden. Excluding a narrow buffer that extends a few kilometers into the sea, the grid is masked in regions beyond this domain and over the ocean due to the absence of in-situ observations. Utilizing the Lambert Azimuthal Equal Area projection as its coordinate reference system, the grid spacing is of 1 km in both the Easting and Northing directions. Specifically, its dimensions span 1550 units in Easting and 2020 in Northing. Figures 5-7 graphically represent this spatial domain.

On accessing files from the CDS, users receive individual files tailored to each specific day, variable, and requested NGCD-type. Notably, these fields carry a time dimension, which consistently measures a length of one.

Product content examples

Figures 8-10 provide illustrations of NGCD products for two distinct days.

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Figure 10: Daily minimum and maximum temperatures (TN top row, TX bottom row, oC) for 30 May 2021: NGCD-1 in the left column; NGCD-2 in the right column.

Data usage acknowledgments

All users of NGCD must provide clear and visible attribution to the Copernicus programme and are asked to cite and reference the dataset provider. Acknowledge according to the licence to use Copernicus Products.

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We acknowledge the data providers in the ECA&D project. Klein Tank, A.M.G. and Coauthors, 2002. Daily dataset of 20th-century surface air temperature and precipitation series for the European Climate Assessment. Int. J. of Climatol., 22, 1441-1453. Data and metadata available at https://www.ecad.eu

Appendix A - Evaluation of version 18.03

The evaluations presented in this Appendix for Temperature and Precipitation are based on NGCD version 18.03 and the data used covers the 46-year period from 1971 to 2016.

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Figure A14: Bias score (dimensionless) of daily precipitation totals (RR) for events exceeding given thresholds (0.1,0.5,1,5,10 and 25 mm) for NGCD-1 (black boxes) and NGCD-2 (red boxes).

Appendix B - Example file structure

Example file structure can be seen directly from the web-browser at the following URLs.

References

Klein Tank, A. M., Wijngaard, J. B., Können, G. P., Böhm, R. , Demarée, G. , Gocheva, A. , Mileta, M., Pashiardis, S. , Hejkrlik, L. , Kern‐Hansen, C. , Heino, R. , Bessemoulin, P. , Müller‐Westermeier, G. , Tzanakou, M. , Szalai, S. , Pálsdóttir, T. , Fitzgerald, D. , Rubin, S. , Capaldo, M. , Maugeri, M. , Leitass, A. , Bukantis, A. , Aberfeld, R. , van Engelen, A. F., Forland, E. , Mietus, M. , Coelho, F. , Mares, C. , Razuvaev, V. , Nieplova, E. , Cegnar, T. , Antonio López, J. , Dahlström, B. , Moberg, A. , Kirchhofer, W. , Ceylan, A. , Pachaliuk, O. , Alexander, L. V. and Petrovic, P. (2002), Daily dataset of 20th‐century surface air temperature and precipitation series for the European Climate Assessment. Int. J. Climatol., 22: 1441-1453. doi:10.1002/joc.773

Info
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This document has been produced in the context of the Copernicus Climate Change Service (C3S).

The activities leading to these results have been contracted by the European Centre for Medium-Range Weather Forecasts, operator of C3S on behalf of the European Union (Delegation Agreement signed on 11/11/2014 and Contribution Agreement signed on 22/07/2021). All information in this document is provided "as is" and no guarantee or warranty is given that the information is fit for any particular purpose.

The users thereof use the information at their sole risk and liability. For the avoidance of all doubt , the European Commission and the European Centre for Medium - Range Weather Forecasts have no liability in respect of this document, which is merely representing the author's view.

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