The Global Precipitation Climatology Project (GPCP)—Means, Variations, and Trends over the Satellite Era

The GPCP is an international effort with the current operational CDR products produced under NOAA support. These CDR products have been cited in over 4000 journal articles, indicating their frequent use in a wide variety of topics and applications. The GPCP is described, focusing on its monthly product, a globally complete precipitation analysis based on satellite and gauge information for the period 1979 to the present. An interim monthly product, available within ten days of the end of the month allows for real-time climate analysis against the long-term climatology. The input data and analysis techniques are described, along with efforts to provide a consistent, homogeneous product useful for accurate estimation of trends and changes.

Means, variations and trends in global total precipitation and patterns of change are described and compared to climate model results. The planetary mean estimate is 2.69 mm/d (+/- 7%) and is generally confirmed by comparisons with TRMM and GPM estimates in the tropics and CloudSat estimates at higher latitudes. Inter-annual and inter-decadal variations, including ENSO, volcanoes and the PDO are presented. Although the global total precipitation shows a very small increase (~1%/K) over the 1979-2017 period of global warming, the tropics show a significant increase in the mean centered on the latitude of the ITCZ, with mid-latitudes in the northern hemisphere showing a decrease. Significant trends in rainfall intensity at the monthly time scale are also noted in the tropics (30^oN-30^oS), with larger rainfall magnitudes increasing, and low rainfall values decreasing, with dry areas expanding. These characteristics are compared to climate model results for calculations over the same period with results indicating some similarities, but also significant differences.

Plans for inclusion of new data sets and new techniques into the next version of the GPCP will also be discussed.