Resources

Global Network of Isotopes in Precipitation

Welcome to the Global Network of Isotopes in Precipitation (GNIP) and its associated database. The IAEA's Water Resources Programme and the World Meteorological Organization (WMO) have been surveying the content of hydrogen and oxygen isotopes in precipitation since 1961. The data are used for a variety of purposes in the fields of hydrology, oceanography and hydrometeorology and in investigations related to the Earth's water cycle and climate changes.

Description and Mode of Operation


General

The International Atomic Energy Agency (IAEA), in cooperation with the World Meteorological Organization (WMO), is conducting a worldwide survey of oxygen and hydrogen isotope content in precipitation. The programme was initiated in 1958 and became operational in 1961. The main initial objective was the systematic collection of basic data on isotope content of precipitation on a global scale to determine temporal and spatial variations of environmental isotopes in precipitation and, consequently, to provide basic isotope data for the use of environmental isotopes in hydrological investigations within the scope of water resources inventory, planning and development.

Although this primary objective remains as an important factor, in recent years, two other objectives have attracted increasing interest: (i) providing input data to verify and further improve atmospheric circulation models, and (ii) the study of climate changes.

Precipitation samples are collected in cooperation with WMO, national meteorological services and national authorities. The samples are analysed in the IAEA's Isotope Hydrology Laboratory in Vienna, and in cooperating laboratories. Each contributing laboratory is responsible for the accuracy and precision of its own analyses. Thanks are due to these and other laboratories which have contributed data from individual collections. GNIP data may be used freely, provided the source is acknowledged.

The role and potential use of the GNIP data were reviewed in the International Workshop on "Tracing isotopic composition of past and present precipitation - opportunities for climate and water studies", which was held in Rüttihubelbad, near Bern, Switzerland, from 23—25 January 1995. The steps to be taken for strengthening the GNIP activities and a new framework of operation, including other international organizations and national networks, were discussed during a Consultants' Meeting on "Operational Aspects of the Global Network "Isotopes in Precipitation", held in Vienna from 7—10 November 1995.

The long-standing collaboration between WMO and IAEA has progressively strengthened year after year, leading to the ratification in December 1998 of the Memorandum of Understanding between WMO and IAEA relating to the Global Network of Isotopes in Precipitation. The MoU leads also to the creation of a Scientific Steering Committee (SSC). The scope of the GNIP-SSC, as defined in the Memorandum of Understanding is to "provide advice to the IAEA and WMO on matters related to the GNIP and to the GNIP Data Base". The work plan and recommendations can be found in the first , second and third GNIP-SSC meeting reports.

Scientific Background: The GNIP Booklet

The GNIP booklet transmit the necessary scientific background rather by images than by scientific reasoning. This booklet aims at stimulating interest in further reading.

Data Collection


IAEA/WMO Isotopes-in-Precipitation Network

Since 1961, more than 800 meteorological stations in 101 countries have been collecting monthly precipitation samples for the Global Network of Isotopes in Precipitation. (The locations of the stations which contributed to this database are shown in Fig. 1.)

Fig. 1. Geographical distribution of the meteorological stations belonging to the IAEA/WMO Global Network of Isotopes in Precipitation (GNIP).

Stations participating in the network collect monthly composite total rainfall, for tritium, deuterium and oxygen-18 analysis. The technical procedure for rain sampling can be found here in English, French or Spanish. Samples are then shipped to various laboratories for analysis. At present, approximately 40% of the stable isotope and of the tritium samples from all network stations are sent to the IAEA Laboratory in Vienna for analysis. The remainder is forwarded to co-operating laboratories for analysis of either tritium, or deuterium and oxygen-18, or both.

National network data

The data collected on a routine basis by stations belonging to national networks are provided to the IAEA and are included in this database, if they are compatible with the present data reporting system. The national networks provide actually 60% of the data of the global database. There is a need for further national networks to meet the scientific communities’ requirements for more (and more accurate) data on isotopes in present-day atmospheric water.

Full acknowledgement should be given to the national authorities, institutes and laboratories involved or supporting the national networks (citing the GNIP database).

Station and Sample Information


Station data

Certain basic information is, whenever available, given for each station or location for which isotope data are reported. Other basic information has been taken from WMO publications [ 1,2, 3 ] or was received in answer to enquiries made to WMO or co-operating laboratories submitting the isotope data. This information includes the following items:

Index number

The system of station index numbers is based on the one evolved by WMO for identifying observation stations, but the numbers, names and locations used in the IAEA network sometimes differ from those employed by WMO. This number has the general format II iii jj, i.e. the block number (II), the station number (iii) and the substation number (jj). Locations for which samples are available are hereafter referred to as stations for brevity.

Each station has a block number (II) which parallels the WMO block number and defines the area from which the isotopic data come. Each station has a station number (iii) which parallels the WMO station number. These correspond to a common block number (II), except Block 89, and are usually distributed so that the zone covered by the block number is divided into horizontal strips of one or several degrees of latitude. Where possible, station numbers within each strip increase from west to east and the first figure of the three-figure station number increases from north to south.

Station index numbers for samples from the Antarctic are allocated under a special WMO scheme.

In addition, each station has a substation number (jj) for which the WMO index system does not have an equivalent. When the sampling station corresponds to the location of a WMO station, the substation number will be 00. When a sampling station is located far from any WMO station it is assigned the block code and station number of the nearest WMO station and is given the substation code number 01, 02, 03, etc.

In all respects other than the substation number, index numbers for isotope sampling stations correspond to the WMO station indexing number.

Name

Official WMO station names are used for those meteorological stations participating in the IAEA/WMO network. The best known geographic name or the name used by the laboratory submitting the data is used in other cases.

Latitude and longitude

Latitude and longitude are given in degrees and hundredths.

Altitude

The altitude is given in metres above (below) mean sea level. For WMO stations it is the elevation of the average level of the terrain in the immediate vicinity of the sampling location.

Meteorological data


General

The great majority of annual and monthly meteorological data for network stations are supplied by the local authorities in charge of the stations. For some of the network stations and for most of the non-network stations meteorological data were compiled from WMO publications [1, 3] .

Precipitation

Precipitation is given in millimetres (mm). The total monthly precipitation values are rounded off to the nearest unit for data entered before 2000. Therefore, trace amounts of precipitation in a given month would appear as 0 if they are less than 0.5 mm. After 2000 the precipitation data is given in mm and tenth.

Type of precipitation

The type of precipitation falling during the month is given when known. 1-rain, 2-snow, 27-rain+snow, 28-precipitation (type not known).

Vapour pressure

Water vapour pressure is given in millibars (mb). The vapour pressure values have been calculated from temperature and relative humidity.

Temperature

The temperature is given in degrees Celsius and tenths.

Sample/analysis information


Date of sampling

The samples are usually composites from the total precipitation at a station during one month. The time of collection is identified under the columns year and month. For a given month, the day entered is 15 and the date accuracy is month. For daily or event-based samples, the sampling day has been entered.

Tritium concentration

The tritium content in each sample is given in tritium units (TU) and has been corrected for decay to the middle of the month. One TU is defined as one atom of tritium per 10^18 atoms of hydrogen, equivalent to 0.118 becquerels (Bq) per litre of water. The tritium half-life has been fixed as 12.32 years [4] for data from 2000.

The analytical error for tritium analysis is given in TU when known. Each contributing laboratory is responsible for the accuracy and precision of its own analyses.

Deuterium/oxygen-18 concentration

Deuterium and oxygen-18 contents of the samples are measured on a mass spectrometer as ratios of deuterium/hydrogen and oxygen-18/O-16 . They are expressed in terms of the per mille deviation of the isotope ratio from a standard. The measurements reported here have a long term precision of about +- 0.1per mil for oxygen-18 and +- 1per mil for deuterium, at one standard deviation level.

The reference standard used is called Vienna-SMOW (Standard Mean Ocean Water) as defined by Craig [5] and Gonfiantini [6]. The data are expressed in dimensionless delta values as defined by:

Quality of the Data

To date, more than 90,000 isotope values have been accumulated in the GNIP database. A critical analysis of the quality of the stored information was recently carried out. In the first instance, obvious errors in the database (typing mistakes, reversed signs, etc.) were eliminated. The second part of the data cleaning procedure consisted of rejection of outliers, identified according to the chosen statistical criteria [7]. In a few cases, a substantial portion of the available data record had to be removed from the database. This concerns stations where errors in the sample collection procedure were identified.

The database undergoes frequent updating: new data, corrections or revisions received from participating laboratories are introduced at regular intervals.

In several cases, the tritium values reported for a given station substantially exceed the expected level, indicating local sources of technogenic tritium and/or contamination during collection of the samples (e.g. Bern, Switzerland; St. Petersburg, Russia).

Availability of the Data

Data collected from 1961 to 1992 has been published by the IAEA in the Technical Reports Series [10].

This publication has been discontinued in the form of printed Technical Reports. The entire, cleaned database is now available for downloading in the form of CSV files.

The statistical evaluation of isotope and meteorological data accumulated up to the end of 1987 has been published as IAEA Technical Reports Series No. 331, entitled "Statistical Treatment of Data on Environmental Isotopes in Precipitation" [7]. In this publication, tables and graphs are presented for each station, illustrating the most characteristic features of the accumulated data. An updated and revised document has been recently prepared. The data accumulated until the end of 1997 have been considered in this new evaluation.

The basic features of the spatial and temporal distribution of deuterium and oxygen-18 in global precipitation, as derived from the IAEA/WMO database, have been discussed in a review paper [9].

References

  1. WORLD METEOROLOGICAL ORGANIZATION, Climatological Normals (Clino) for climate and climate ship stations for the period 1932-1960, WMO/OMM No. 17, TP.52.
  2. WORLD METEOROLOGICAL ORGANIZATION, Weather Reporting, Volume A: Observing Stations, WMO/OMM No. 9, TP.4.
  3. WORLD METEOROLOGICAL ORGANIZATION in Co-operation with Environmental Science Services Administration USA, Monthly Climatic Data for the World, United States Government Printing Office, monthly editions.
  4. LUCAS, L. L., UNTERWEGER, M. P., Comprehensible Review and Critical of the Half-life of Tritium. Journal of Research of the National Institute of Standards and Technology, 105-4 (2000), 541-549.
  5. CRAIG, H., Standard for reporting concentration of deuterium and oxygen-18 in natural waters, Science 113 (1961) 1833.
  6. GONFIANTINI, R., Standard for stable isotope measurements in natural compounds, Nature (London) 271 (1978) 534-536.
  7. INTERNATIONAL ATOMIC ENERGY AGENCY, Statistical Treatment of Data on Environmental Isotopes in Precipitation, Technical Reports Series No. 331, IAEA, Vienna (1992) 781.
  8. TAYLOR, C.B., Stable Isotope Composition of Monthly Precipitation Samples Collected in New Zealand and Rarotonga, Physical Science Rep. 3, Dept. of Scientific and Industrial Research, Lower Hutt, New Zealand (1990) 93.
  9. ROZANSKI, K., ARAGUAS ARAGUAS, L., GONFIANTINI, R., Isotope Patterns in Modern Global Precipitation, Geophysical Monograph 78. In: Climate Change in Continental Isotope Records, American Geophysical Union (1993) 1-36.
  10. INTERNATIONAL ATOMIC ENERGY AGENCY. Environmental Isotope Data No. 1-10: World Survey of Isotope Concentration in Precipitation.
    • No. 1 (STI/DOC/10/96) 1953-1963, 421 pages, published in 1969
    • No. 2 (STI/DOC/10/117) 1964-1965, 404 pages, published in 1970
    • No. 3 (STI/DOC/10/129) 1966-1967, 421 pages, published in 1971
    • No. 4 (STI/DOC/10/147) 1968-1969, 404 pages, published in 1973
    • No. 5 (STI/DOC/10/165) 1970-1971, 421 pages, published in 1975
    • No. 6 (STI/DOC/10/192) 1972-1975, 404 pages, published in 1979
    • No. 7 (STI/DOC/10/226) 1976-1979, 421 pages, published in 1983
    • No. 8 (STI/DOC/10/264) 1980-1983, 404 pages, published in 1986
    • No. 9 (STI/DOC/10/311) 1984-1987, 188 pages, published in 1990
    • No. 10 (STI/DOC/10/371) 1988-1991, 200 pages, published in 1994