Global Precipitation: Means, Variations and Trends During the Satellite Era (1979–2014)

Abstract

Global precipitation variations over the satellite era are reviewed using the Global Precipitation Climatology Project (GPCP) monthly, globally complete analyses, which integrate satellite and surface gauge information. Mean planetary values are examined and compared, over ocean, with information from recent satellite programs and related estimates, with generally positive agreements, but with some indication of small underestimates for GPCP over the global ocean. Variations during the satellite era in global precipitation are tied to ENSO events, with small increases during El Ninos, and very noticeable decreases after major volcanic eruptions. No overall significant trend is noted in the global precipitation mean value, unlike that for surface temperature and atmospheric water vapor. However, there is a pattern of positive and negative trends across the planet with increases over tropical oceans and decreases over some middle latitude regions. These observed patterns are a result of a combination of inter-decadal variations and the effect of the global warming during the period. The results reviewed here indicate the value of such analyses as GPCP and the possible improvement in the information as the record lengthens and as new, more sophisticated and more accurate observations are included.

The Global Precipitation Climatology Project (GPCP) Monthly Analysis (New Version 2.3) and a Review of 2017 Global Precipitation

“…The ocean and land values in Figure 8a "flip-flop" between El Niño and La Niña years, with the global total value having smaller year-to-year variations, although being larger during El Niño years (e.g., 1998, 2010, 2015-2016) [16]. The year 2017, a weak La Niña year, has an estimated record-setting high GPCP land value, compensated by a relatively low ocean value.…”

“…Over land, most of the changes are due primarily to the change to the GPCC V7 Full gauge analysis. A detailed summary of climatological values, inter-annual variations, and trends using the GPCP V2.3 is given in [16], along with a summary of the comparisons with the recent precipitation estimates from the Tropical Rainfall Measuring Mission (TRMM) and CloudSat.…”

“…Although the global trends in Figure 8 are very small, the regional trends are larger and variable in the spatial domain (Figure 9) with the pattern showing an area of positive trend along most of the Inter-Tropical Convergence Zone (ITCZ), especially across the Pacific and Indian Oceans (see also [16]). Oceanic decreases north and south of the Pacific ITCZ are adjacent and weakly connected to decreases over land, including the southwestern U.S. A general scenario of "wet areas getting wetter, dry areas getting drier" is evident.…”

“…At high northern latitudes, the positive trends noted across Eurasia and the Arctic Ocean to Alaska are similar to the positive anomaly features seen in Figure 6 for 2017. Adding one year (2017) to the data set does not significantly change the pattern in Figure 9, but also serves as a starting point for examining regional trends in relation to ENSO, inter-decadal variations, and global warming (see [16,20]). Data from 2017 have also been incorporated into the investigation of trends in rainfall intensity using the monthly GPCP analyses [21].…”

Global Precipitation Trends across Spatial Scales Using Satellite Observations

“…Those that do emphasize observations tend to focus on a single geographical area at a regional scale as a compliment to a single form of global analysis, rather than shaping the global discussion around varying methods of spatial division. Other studies (Adler et al 2017;Gu et al 2016;Wang et al 2016;Gu and Adler 2013) use the Global Precipitation Climatology Project (GPCP) at 2.5° resolution to investigate global precipitation trends, but they lack the high resolution needed to do so at varying spatial scales. This is especially important for divisions with highly irregular borders such as political boundaries and watersheds.…”