Alberta West News: What is the trend in aggregate precipitation, year over year, on Earth's continents in comparison to precipitation over the oceans?

Sunday, June 29, 2025

What is the trend in aggregate precipitation, year over year, on Earth's continents in comparison to precipitation over the oceans?

Aggregate precipitation trends over Earth's continents and oceans both show increases over recent decades, but the magnitude, spatial patterns, and year-over-year variability differ between land and ocean regions.

Continental (Land) Precipitation Trends

Global precipitation over land has increased at an average rate of about 0.03 inches per decade since 1901, with certain regions (such as the contiguous U.S.) experiencing higher rates of increase (0.18 inches per decade)1.
Extreme precipitation events over land have become more frequent and intense. Studies indicate that since about 1950, the number of heavy precipitation events over land has increased in more regions than it has decreased. About two-thirds of global land-based weather stations show increases in annual maximum daily rainfall (Rx1day), with the increase per 1 K rise in global mean surface temperature ranging from 5.9% to 7.7%, closely matching theoretical expectations23.
The increase is not uniform: some areas, like eastern North America, Europe, and South Africa, show stronger upward trends, while others (such as the Canadian Prairies, parts of the western U.S., Australia, and northern China) have seen decreases or weaker trends21.
Regional variability is high: While some subtropical dry regions (e.g., western US, southern Africa) have seen smaller increases or even decreases, wetter regions in the tropics and mid-latitudes have experienced larger increases in rainfall records3.

Oceanic Precipitation Trends

Mean annual precipitation over the oceans has also increased, but the rate and spatial distribution depend on the dataset and methodology used. The latest satellite-based products (e.g., GPM, GPCP) show increases in mean oceanic precipitation rates, with recent versions reporting up to 18% higher values compared to earlier versions, largely due to improved detection of light precipitation4.
Satellite datasets generally show increasing trends in oceanic precipitation, especially in the deep tropics and high latitudes, consistent with the "wet gets wetter, dry gets drier" (WWDD) paradigm. These increases are most pronounced near the equator and in high-latitude ocean regions45.
Reanalysis datasets, however, sometimes show declines in precipitation in key oceanic regions like the Intertropical Convergence Zone (ITCZ) and North Atlantic, which contradicts the WWDD pattern. This highlights ongoing uncertainties and the importance of using multiple datasets for robust conclusions5.
Model projections (e.g., IPCC AR4) estimate that by the late 21st century, precipitation over land will increase by about 5%, and over oceans by about 4%, with the land accounting for a slightly smaller share of the global increase than its areal proportion6.

Land vs. Ocean Comparison

Trend Aspect	Continents (Land)	Oceans
Long-term trend	Increase (0.03 in/decade global avg)1	Increase (up to 18% in recent satellite products)4
Year-over-year variability	High; strong regional differences2 1	High; discrepancies among datasets, especially between satellites and reanalyses5
Extremes	Marked increase in frequency and intensity2 3	Increases in wet regions, especially tropics and high latitudes4 5
Dataset agreement	Generally strong	Satellite products agree; reanalyses less consistent5
Spatial pattern	Regional increases and decreases; subtropics may dry2 3 1	Tropics and high latitudes wetter; some midlatitude declines in reanalyses4 5

Summary

Both continents and oceans are experiencing increasing aggregate precipitation over recent decades, with the largest increases in wetter regions, especially the tropics and higher latitudes.
Land areas show a clear and robust trend toward more frequent and intense precipitation events.
Oceanic trends are positive in most satellite-based datasets but can vary in reanalyses, particularly in the tropics and ITCZ.
Uncertainties remain due to differences in observational coverage, measurement techniques, and dataset methodologies, particularly over the oceans45.

Overall, the trend is upward for both continents and oceans, but the details—such as spatial distribution, magnitude, and agreement among datasets—differ, with land-based trends being more robust and oceanic trends more dataset-dependent.

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