Contributors: Cristian Lussana (MET Norway)
Issued by: Cristian Lussana (MET Norway)
Issued Date: 30/08/2023
Ref: M311_Lot3.3.1.4_NGCD_PUG_ver0.2
Official reference number service contract: C3S2 311 Lot3
History of modifications
List of datasets covered by this document
Related documents
| Reference ID | Document |
|---|---|
D1 | NGCD Algorithm Theoretical Basis Document |
D2 | NGCD Product User Guide and Specifications (PUGS) |
D3 | Climate and Forecast (CF) Conventions and Metadata; http://cfconventions.org |
D4 | 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 | |
MET Norway | |
KNMI | |
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 |
ECA&D |
Data access information
| Description | Link |
|---|---|
| NGCD climate indices ver. 23.03 (full update based on NGCD historical archive) | https://thredds.met.no/thredds/catalog/ngcd/version_23.03/indices/catalog.html |
| NGCD climate indices ver. 22.03 (full update based on NGCD historical archive) | https://thredds.met.no/thredds/catalog/ngcd/version_22.03/indices/catalog.html |
| NGCD climate indices provisional ver. 23.03 (monthly updates based on NGCD provisional archive) | https://thredds.met.no/thredds/catalog/ngcd/provisional/indices/catalog.html |
| NGCD is available to users via the Climate Data Store | https://cds.climate.copernicus.eu/cdsapp#!/dataset/insitu-gridded-observations-nordic?tab=overview |
| NGCD is also available to users via MET Norway OPeNDAP access | https://thredds.met.no/thredds/catalog/ngcd/catalog.html |
There are no "Known issues" at the moment.
Scope of the document
This document is the user guide for the climate indices derived from the NGCD observational gridded dataset. The climate indices and NGCD are 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 main aim of this document is to aid the user in understanding the features and limitations of the data, and then to enable them to read and use the data.
Executive summary
Indices of extremes are derived indicators that can be used to monitor the climate. Examples of these indices are the number of frost days in winter or the annual number of rainy days. Some indices have a fixed threshold and therefore are only useful in certain areas, at certain times, such as the number of ice days which reflect the number of days when the maximum daily temperature is below zero. Other indices are calculated with respect to the local climate, such as the number of very heavy precipitation days, calculated as the number of days when the daily precipitation is higher than the 95th percentile for a reference period at that specific location. A large number of indices use only temperature or only precipitation as input, while a few others require more than one variable as input. The indices dataset presented here uses the NGCD gridded dataset as the input from which the indices are derived.
Product information
Product description
NGCD is an observational gridded dataset covering Fennoscandia (Finland, Norway and Sweden) based on in-situ observations only. The variables included in the dataset are: daily mean temperature; daily maximum temperature; daily minimum temperature; and daily total precipitation. NGCD consists of two independent datasets, NGCD-1 and NGCD-2. NGCD is released in versions, which are labelled as Year.Month (e.g. the update in March 2023 yields ver. 23.03). Each version is made up of two archives: i) the historical archive and ii) the provisional archive.
NGCD is described in detail in the documents NGCD Algorithm Theoretical Basis Document and NGCD Product User Guide and Specification (PUGS).
Climate indices are derived from the daily NGCD datasets and the key characteristics of the datasets are reported in Table 1.
The methods and elaboration are briefly described in Table 2 (column Description).
We distinguish between five main types of climate indices Table 2 (column Type):
- Rain indices
- Heat indices
- Cold indices
- Drought indices
- Multi-element indices
Each index is assigned to one of these five categories.
The climate indices are provided on a regular grid, using a Lambert Azimuthal Equal Area coordinate reference system, with a spacing of 1 km in both Easting and Northing directions.
For each of the indices, the fields are provided both for NGCD-1 and NGCD-2. In addition, NGCD provides a provisional archive, in between two subsequent versions of the historical archive. For the provisional archive, a reduced set of monthly climate indices is provided, which are based on NGCD-2 only. The final fields are stored in data files in netCDF-4 format.
NGCD climate indices are fully updated once a year, in June, on the basis of the most recent NGCD historical archive available. Each update is then linked to a specific NGCD version (e.g. the update in June is linked to the NGCD historical archive produced in March 2023, which yields ver. 23.03). The newest updated climate indices are based on NGCD ver. 23.03 and they cover the time period from January 1971 to December 2022. In addition, for each month we provide monthly climate indices based on the NGCD ver. 23.03 provisional archive.
The next release of fully updated NGCD climate indices is scheduled for June 2024 and the indices will be based on NGCD historical archive ver 24.03 (scheduled for March 2024).
Data Overview
Table 1: Overview of key characteristics of the indices derived from NGCD
Data Description | |
Dataset title | Indices derived from NGCD |
Data type | Indicators derived from gridded observations |
Topic category | Climate Monitoring |
Sector | Applicable to various sectors |
Keyword | Climate indices |
Dataset language | eng |
Domain | Finland, Norway and Sweden |
Horizontal resolution | 1 km x 1 km |
Temporal coverage | 1971-01-01/to/2022-12-31 |
Temporal resolution | Monthly / seasonal / half-yearly / annual / daily (depending on the index) |
Update frequency | Annual (in June) |
Version | ver. 23.03 (based on NGCD ver 23.03) |
Provider | the Norwegian Meteorological Institute (MET Norway) |
Terms of Use | The NGCD based Climate Indices as a derived dataset can be provided under the Copernicus licence. |
Variable Description
Table 2: Overview and description of variables.
| Variables | ||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Long Name | Short Name | Unit | Type | Description | ||||||||||||||||
Number of Frost Days | FD | Days | Cold | The number of days in a given period when the daily minimum temperature is less than 0°C. | ||||||||||||||||
Maximum number of consecutive frost days | CFD | Days | Cold | The largest number of consecutive days in a given period when the daily minimum temperature is less than 0°C. | ||||||||||||||||
Number of Ice Days | ID | Days | Cold | The number of days in a given period when the daily maximum temperature is less than 0°C. | ||||||||||||||||
Heating degree days | HD17 | °C | Cold | The heating degree days index accumulates the temperature difference between daily mean temperature TG and the threshold of 17°C (17°C−TG), for the days when the daily mean temperature drops below 17°C, for a given period. | ||||||||||||||||
Growing season length | GSL | Days | Cold | The number of days between the first occurrence of at least 6 consecutive days when the daily mean temperature exceeds 5°C and the first occurrence after 1 July of at least 6 consecutive days when the daily mean temperature drops below 5°C. | ||||||||||||||||
Minimum value of daily maximum temperature | TXn | °C | Cold | The minimum value of the daily maximum temperatures in a given period. | ||||||||||||||||
Minimum value of daily minimum temperature | TNn | °C | Cold | The minimum value of the daily minimum temperatures in a given period. | ||||||||||||||||
Percentage of cold nights | TN10p | % | Cold | The percentage of days in a given period when the daily minimum temperature is less than the 10th percentile of daily minimum temperatures for the 5-day windows centred on each calendar day in the corresponding climatological period for 1961-1990. | ||||||||||||||||
Percentage of cold day-times | TX10p | % | Cold | The percentage of days in a given period when the daily maximum temperature is less than the 10th percentile of daily maximum temperatures for the 5-day windows centred on each calendar day in the corresponding climatological period for 1961-1990. | ||||||||||||||||
Cold-spell duration index | CSDI* | Days | Cold | The largest number of consecutive days in a given period when the daily minimum temperature is less than the 10th percentile of daily minimum temperatures for the 5-day windows centred on each calendar day in the corresponding climatological period for 1961-1990, in intervals of at least six consecutive days. | ||||||||||||||||
Number of Summer days | SU | Days | Heat | The number of days in a given period when the daily maximum temperature is higher than 25°C. | ||||||||||||||||
Maximum number of consecutive summer days | CSU | Days | Heat | The largest number of consecutive days in a given period when the daily maximum temperature is higher than 25°C. | ||||||||||||||||
Number of Tropical nights | TR | Days | Heat | The number of days in a given period when the daily minimum temperature is higher than 20°C. | ||||||||||||||||
Maximum value of daily maximum temperature | TXx | °C | Heat | The maximum value of the daily maximum temperatures in a given period. | ||||||||||||||||
Maximum value of daily minimum temperature | TNx | °C | Heat | The maximum value of the daily minimum temperatures in a given period. | ||||||||||||||||
Percentage of warm nights | TN90p | % | Heat | The percentage of days in a given period when the daily minimum temperature is higher than the 90th percentile of daily minimum temperatures for the 5-day windows centred on each calendar day in the corresponding climatological period for 1961-1990. | ||||||||||||||||
Percentage of warm day-times | TX90p | % | Heat | The percentage of days in a given period when the daily maximum temperature is higher than the 90th percentile of daily maximum temperatures for the 5-day windows centred on each calendar day in the corresponding climatological period for 1961-1990. | ||||||||||||||||
Warm-spell duration index | WSDI* | Days | Heat | The largest number of consecutive days in a given period when the daily maximum temperature is higher than the 90th percentile of daily maximum temperatures for the 5-day windows centred on each calendar day in the corresponding climatological period for 1961-1990, in intervals of at least six consecutive days. | ||||||||||||||||
Mean of diurnal temperature range | DTR | °C | Multi | The mean value in a given period of the difference between the daily maximum temperature and daily minimum temperature (daily maximum - daily minimum). | ||||||||||||||||
Maximum number of consecutive dry days (daily precipitation < 1 mm) | CDD* | Days | Drought | The largest number of consecutive days in a given period when the daily precipitation is less than 1 mm. | ||||||||||||||||
Huglin Index for grape growth suitability | HI | [-] | Multi | The Huglin index accumulates the mean of the temperature difference between the daily mean temperature (TG) and the threshold of 10°C (TG - 10°C), and the temperature difference between the daily maximum temperature (TX) and the threshold of 10°C (TX - 10°C), for the days when the daily mean temperature exceeds 10°C. The accumulation is multiplied by a latitudinal coefficient for day length, K. The period of accumulation is 1 April to 30 September. The value of K is determined using:
Each specific grape variety has a specific range of Huglin Index values for which it thrives (https://en.wikipedia.org/wiki/Huglin_index). | ||||||||||||||||
3-Month Standardized Precipitation Index | SPI-3 | [-] | Drought | SPI is a probability index based on precipitation. It is designed to be a spatially invariant indicator of drought. SPI3 refers to precipitation in the previous 3-month period (positive values indicate a wet period; negative values indicate a dry period). | ||||||||||||||||
6-Month Standardized Precipitation Index | SPI-6 | [-] | Drought | SPI is a probability index based on precipitation. It is designed to be a spatially invariant indicator of drought. SPI6 refers to precipitation in the previous 6-month period (positive values indicate a wet period; negative values indicate a dry period). | ||||||||||||||||
Highest 1-day precipitation amount | RX1day | mm | Rain | The maximum value of the one-day precipitation amount in a given period. | ||||||||||||||||
Highest 3-day precipitation amount | RX3day | mm | Rain | The maximum value of the consecutive three-day precipitation amount in a given period. | ||||||||||||||||
Highest 5-day precipitation amount | RX5day | mm | Rain | The maximum value of the consecutive five-day precipitation amount in a given period. | ||||||||||||||||
Simple daily intensity index | SDII | mm/day | Rain | The mean value of daily precipitation amount on wet days (when the daily precipitation is equal to or larger than 1 mm) in a given period. | ||||||||||||||||
Number of Wet days | R1mm | Days | Rain | The number of days in a given period when the daily precipitation amount is equal to or larger than 1 mm. | ||||||||||||||||
Number of Heavy precipitation days | R10mm | Days | Rain | The number of days in a given period when the daily precipitation amount is equal to or larger than 10 mm. | ||||||||||||||||
Number of Very heavy precipitation days | R20mm | Days | Rain | The number of days in a given period when the daily precipitation amount is equal to or larger than 20 mm. | ||||||||||||||||
Maximum no of consecutive wet days | CWD* | Days | Rain | The largest number of consecutive days in a given period when the daily precipitation amount is equal to or is larger than 1 mm. | ||||||||||||||||
Precipitation fraction due to moderate wet days | R75pFRAC | % | Rain | The percentage of days in a given period when the daily precipitation amount is higher than the 75th percentile of the daily precipitation amounts for the 5-day windows centred on each calendar day in the corresponding climatological period for 1961-1990. | ||||||||||||||||
Precipitation fraction due to very wet days | R95pFRAC | % | Rain | The percentage of days in a given period when the daily precipitation amount is higher than the 95th percentile of the daily precipitation amounts for the 5-day windows centred on each calendar day in the corresponding climatological period for 1961-1990. | ||||||||||||||||
Precipitation fraction due to extremely wet days | R99pFRAC | % | Rain | The percentage of days in a given period when the daily precipitation amount is higher than the 99th percentile of the daily precipitation amounts for the 5-day windows centred on each calendar day in the corresponding climatological period for 1961-1990. | ||||||||||||||||
Precipitation total due to moderate wet days | R75pTOT | mm | Rain | The accumulated daily precipitation amount in a given period for the days when the daily precipitation amount is higher than the 75th percentile of the daily precipitation amounts for the 5-day windows centred on each calendar day in the corresponding climatological period for 1961-1990. | ||||||||||||||||
Precipitation total due to very wet days | R95pTOT | mm | Rain | The accumulated daily precipitation amount in a given period for the days when the daily precipitation amount is higher than the 95th percentile of the daily precipitation amounts for the 5-day windows centred on each calendar day in the corresponding climatological period for 1961-1990. | ||||||||||||||||
Precipitation total due to extremely wet days | R99pTOT | mm | Rain | The accumulated daily precipitation amount in a given period for the days when the daily precipitation amount is higher than the 99th percentile of the daily precipitation amounts for the 5-day windows centred on each calendar day in the corresponding climatological period for 1961-1990. | ||||||||||||||||
Total precipitation on wet days | PRCPTOT | mm | Rain | The accumulated daily precipitation amount on wet days (when the daily precipitation amount is equal to or larger than 1 mm) in a given period. | ||||||||||||||||
*For the calculation of spells (CSDI, WSDI, CDD, CWD) the spells are cut-off at the end of the calendar year. This might interfere with the applications where the continuation of a spell into the next calendar year is relevant. For these applications, additional datasets are provided with the names: altCSDI, altWSDI, altCDD, altCWD.
Data usage information
File naming convention
The data files are in netCDF-4 format and follow the CF-standards.
For the historical archive, the file names have the format:
NGCD_<Index>_<TempAgg>_<CRS>_type<Id_type>_version_<Ver>.nc
Where:
- <Index> is one of the indices reported in Table 2 (column Short Name)
- <TempAgg> temporal aggregation: yr (year); hf (half-year); seas (season); mon (month)
- <CRS> is the coordinate reference system (1km-laea, where "laea" stands for Lambert azimuthal equal-area projection)
- <Id_type> NGCD type: either 1 or 2
- <Ver> NGCD climate indices version (Year.Month)
For the provisional archive, the file names have a similar format. There are some differences though, since in this case we have one file per index and per month. The file names have the format:
NGCD_<Index>_<TempAgg>_<CRS>_type<Id_type>_version_<Ver>_prov_<YearMonth>.nc
Where there is the tag "prov" (stands for provisional) after the version and the time label YearMonth is specified in the file name.
