7A.2 Global and Tropical Precipitation—Trends and Intensity Changes over the Satellite Era

Tuesday, 8 January 2019: 3:15 PM
North 121BC (Phoenix Convention Center - West and North Buildings)
Robert Adler, Univ. of Maryland, College Park, College Park, MD; and G. Gu, J. J. Wang, and G. J. Huffman

Variations and trends in global total precipitation and patterns of change are described using the Global Precipitation Climatology Project (GPCP) monthly product, a globally complete precipitation analysis based on satellite and gauge information for the period 1979 to the present. The results are compared to ensemble climate model results. The planetary mean GPCP (Version 2.3) number is 2.69 mm/d (+/- ~7%), a slight 1% higher than the earlier version. This global number is supported (+/- 5%) by recent comparisons with TRMM and GPM estimates in the tropics and CloudSat estimates at higher latitudes and by global water budget analyses.

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 centered on the latitude of the ITCZ. Mid-latitudes in the northern hemisphere show a decrease, with higher latitudes having an increase, although high latitude estimates from both satellites and gauges require evaluation and improvement. The global map of observed trends shows some general correspondence with that indicated by climate models (both CMIP and AMIP) under a warming climate for the same period, but there are significant remaining differences that need to be further evaluated, both from the satellite and model standpoint.

The GPCP Monthly analysis is also used to examine trends and variations in precipitation intensity in the tropics (30oN-30oS) and compared to AMIP and CMIP climate models. The relative roles of interdecadal (Pacific Decadal Oscillation [PDO]) shift and implied greenhouse gas (GHG) forcing are interpreted by comparing the GPCP observations, AMIP results forced by observed SST, and CMIP Hist-Full runs (no PDO effect). Significant trends in intensity at the monthly time scale are noted with the GPCP analyses, with larger rainfall magnitudes increasing, moderate rainfall values decreasing and dry areas expanding. Similar type variations in daily rainfall intensity are seen on ENSO time scales using the TRMM Multi-satellite Precipitation Analysis (TMPA) 3-hr resolution data for the shorter 1998-2017 period.

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