Updating the GPCP global precipitation datasets

The Global Precipitation Climatology Project (GPCP) is charged with developing global long-term records of precipitation for the international community on behalf of the World Meteorological Organization/World Climate Research Programme/Global Energy and Water Experiment (WMO/WCRP/GEWEX). After an extended period of stable input data and algorithms the GPCP has entered a period in which a variety of upgrades and transitions are needed to enhance and continue extending the data record.

First, in 2009 the GPCP released Version 2.1 of its long-term (1979-present) global Satellite-Gauge data sets to take advantage of the improved Global Precipitation Climatology Centre (GPCC) gauge analysis, which is one key input. As well, the OPI estimates used in the pre-SSM/I era have been rescaled to match a 20-year record of the SSM/I-era SG. The monthly, pentad, and daily GPCP products have been entirely reprocessed, continuing to require that the submonthly estimates sum to the monthly. Version 2.1 is close to Version 2, with the global ocean, land, and total values about 0%, 6%, and 2% higher, respectively. The revised long-term global precipitation rate is 2.68 mm/d. The corresponding tropical (25°N-S) increases are 0%, 7%, and 3%. Long-term linear changes in the data tend to be smaller in Version 2.1, but the statistics are sensitive to the threshold for land/ocean separation and use of the pre-SSM/I part of the record.

Second, the passive microwave sensor being used for calibration is being transitioned presently from the now-defunct F13 SSM/I to the F17 SSMIS. Use of this new sensor has involved close interaction with the SSMIS data providers and members of the user community to ensure that instrument calibrations are understood and that the F17 and F13 precipitation estimates are as consistent as possible.

Third, the GPCP is working toward a new Version 3. The goal is a fully global, finer scale estimate over the entire satellite period of record. There are several important new input data sources available for this effort, including the NOAA National Climatic Data Center's GriSat-B1, a superset of the International Satellite Cloud Climatology Program B1 data, and the new generation of “high-resolution precipitation products”. However, as with the current GPCP, it is likely that Version 3 will feature at least two product lines, with the higher-resolution product reaching back to the mid-1990's, when multiple passive microwave satellites first became available.