Bruno Rudolf Deutscher Wetterdienst, Offenbach, Germany, June 2002

1. The Functions of the Global Precipitation Climatology Centre (GPCC) Bruno Rudolf Deutscher Wetterdienst, Offenbach, Germany, June 2002 • The GPCC has been established in 1988 at Deutscher Wetterdienst (DWD) on invitation by the WMO. • The GPCC contributes to WCRP (GEWEX-GPCP, ACSYS and CLIVAR) and to GCOS.

2. GPCC‘s functions • The primary task of GPCC is operational monitoringand analysis of global land-surface precipitation. • This comprises following specific functions: • Collection of precipitation data disseminated globally via GTS. • Acquisition of additional data from individual countries. • Data quality-control, correction, and error assessment. • Calculation of area-mean precipitation on regular gridboxes. • Dissemination of the gridded data sets. • Development of related methods. • Climate-related applications and studies. • Operation of the Arctic Precipitation Data Archive (ACSYS - APDA).

3. GPCC‘s near real-time “Monitoring Product“ • based on about 7,000 stations • available on web • http://gpcc.dwd.de • used by the GPCP for combination with satellite products • (Precipitation in mm • for December 2001)

4. Required accuracy, errors Users‘ request and goal of the GPCP is it, to provide precipitation with an accuracy of 10% on the gridboxes . The total stochastic error of the raingauge-based gridded precipitation results from three different error types: EQ = Error from undiscovered errors in the input data sets (estimated by statistical comparisons of data from different source) EC = Error from uncertainty of raingauge bias correction (estimated by variation of parameters used) ES = Sampling error of calculation of area-means (statistically based function of data coverage and regional variability)

5. The sampling error as function of network density and variability The sampling error of area-mean precipitation calculated from station-related observations depends on the number of stations used and the regional variabilty of the parameter. The required networkdensity depends on temporal and spatial resolution considered and desired accuracy of the product: a 10%-error on a 2.5° grid requires 40,000 stations! (Fig. after WMO-No. 115, 1985)

6. GPCC data sources • Near realtime: • GTS SYNOP (DWD RH Offenbach) • GTS CLIMAT (DWD RH Offenbach) • GTS CLIMAT (DWD RH Tokyo) • SYNOP-based (NOAA RH Washington) • Non realtime: • Additional data from (so far) 160 countries • International project data (GEWEX and other) • Historical data collections (CRU, FAO, GHCN)

7. GPCC‘s monitoring and merging of near real-time data (which is the data base of the monthly precipitation “Monitoring Product“) • Availability of data from GTS: • all GTS-data • CPC-SYNOP • DWD-SYNOP • DWD-CLIMAT • GSN-Stations

8. GPCC‘s full data base is aimed to meet the accuracy requirements for monthly precipitation Availability of all data including the data received via GTS and data supplied by NMSs of 160 countries up to 40,000 stations. Near real-timedata based on bulletins from GTS (DWD) SYNOP and CLIMAT about 7,000 stations. restricted data

9. GPCC data acquisition activities • Near realtime: • Monitoring of CLIMAT availability and quality • Publication of monitoring results by GSN-MC • Contact to NMSs in case of problems (email) • Non realtime: • WMO circular letters to Members • Individual follow-up requests by GPCC • by letters, email, conferences, visits . . . . . . . .

10. Result of data collection • Problems: • Data not readable • Formats unknown or irregular • Misformatted data • Meta data missing or wrong • Dublicate stations • Irregular data deliveries • Individual data errors • To do: • Reformatting of the data sets • Control of the meta data • Contact supplier (if possible) • Individual investigation • Careful quality control of the data

12. GPCC‘s new high-resolution “Full-Data“ Product for 1986-1995 • based on all collected raingauge data from 28,000 - 40,000 stations • full quality-control for relevant station metadata: location, names, ID-No. • full quality-control for all GTS-based near real-time data • overall visual-quality control of the individually received national data sets Ten years mean annual precipitation (period 1986-1995) in mm per month, gridsize: 0.5° x 0.5°

13. Comparison of GPCC‘s Monitoring and Full-Data Product: Network Density Monitoring Product Full-Data Product ca. 6,500 stations (June 1987) ca. 40,000 stations Number of raingauges used per grid box of 1° by 1° latitude/longitude

14. Comparison of GPCC‘s Monitoring and Full-Data Product Global land-surface mean precipitation in mm per month based on the results on all grid boxes covered by both products

15. Comparison of GPCC‘s Monitoring and Full-Data Product • Summary of first results: • The global land-surface area-averaged monthly precipitation for the Full • Data Product is always higher (up to 10%) than for the Monitoring Product. • One reason may be that mountaineous and heavy rainfall areas are depicted better by the denser network. • Size and sign of the differences of the two products vary from region to region. • The Full Data Product delivers more details, and sharper regional gradients compared to the Monitoring Product. • A more detailled comparison study is planned with respect of the specific • regional conditions.

16. Correction of gauge-measured data due to systematic errors: Remember yesterdays talks.

17. Comparison of global satellite-raingauge combined data sets GPCP-V2 (Huffman et al.) versus CMAP (Xie & Arkin)

18. The Implementation Plan of the Arctic Climate Systeme Study (ACSYS) requested for establishment of an Arctic Precipitation Data Archive (APDA). This archive was installed in 1996 within the Global Precipitation Climatology Center (GPCC) . APDA focuses on the period 1950-2000 and contains both daily and monthly as well as uncorrected and corrected precipitation and snow depth data from all observation stations (as far as available) within the Arctic drainage basin.

19. Extension of GPCC‘s data base by historical data In the beginning, the GPCP was defined to analyse data of the period 1986 to 1995 only. Following later requests of WCRP and GCOS, the GPCC was established as continuing operational activity. The data base has continuously been updated by current data. As there is a strong need for updated long time-series (CLIVAR and GCOS), the GPCC has now started pooling its own data base with the major historical climate data collections of CRU, FAO and GHCN. One of the results will be a Global Land-surface Precipitation Re-analysis complementing ERA-40.

20. The first major task is the harmonization of the stations meta data, which are not unique for the different data collections to be merged.

21. GPCC’s website offers download of gridded precipitation data sets. The “Visualizer” displays digital maps on-the-fly. Various display options can be selected by the user. About 150,000 downloads per year !! http://gpcc.dwd.de/

22. GPCC needs • More regular data deliveries. • Establishment of focal points in the contries for feed back. • Full meta data with regard to stations history and observation method. • Guidance for the correction of systematic gauge error. • Visiting scientists.