Semi OT: Precipitation trends

Using satellite data, Nguyen et al. found that there is no global trend in precipitation. They write:
“The take-home message from our study using the new 33+ years of high-resolution global precipitation dataset is that there seems not to be any detectable and significant positive trends in the amount of global precipitation due to the now well-established increasing global temperature. While there are regional trends, there is no evidence of increase in precipitation at the global scale in response to the observed global warming.”

Certainly unexpected.



To me, that sounds like the total precipitation has not changed, but where it falls has changed. Which seems like what one would expect. Why would a warmer globe cause more or less precipitation … unless it was so hot that it all stayed as vapor? Whereas, things like the West Coast recent rain and snow have clearly changed dramatically.


Basically, more precipitation is expected because warmer air can hold more water vapor and an atmosphere with more water vapor can then make more precipitation. More precisely, the Clausius-Claypeyron equation says that for every degree C increase in air temps the air can hold 7% more moisture.



Maybe you can answer this.

If the climate is warming and it appears it is and it appears must of that energy is being stored in the ocean, then it would follow that in addition to the simple thermal expansion of the water, the ice melt from the glaciers should be forcing a sea level rise.

Has there been a measurable sea level rise in the last 25 years? If there has, can the amount of surface area increases by a measurable amount. And if it has, would not that increase surface evaporation and that evaporation drive increased world wide rain fall.

If this rainfall study is accurate, a lot of stuff is off in surprising ways.



Kind of answered the question with ChatGPT.

“Yes, there has been a measurable sea level rise in the last 25 years, and the rate of sea level rise has been increasing over time. According to the Intergovernmental Panel on Climate Change (IPCC), the global mean sea level has risen by about 15 cm (6 inches) between 1901 and 2018, and the rate of rise has increased from 1.4 mm/year (0.05 inches/year) during the 20th century to 3.7 mm/year (0.15 inches/year) between 2006 and 2018.

The increase in surface area due to sea level rise is also measurable, and it is estimated that the global ocean area has increased by about 1.2 million square kilometers (463,000 square miles) since 1993 due to melting ice and thermal expansion of the ocean.”

So even more interesting about the rain fall study.



There is the fun. The cooler temp needed to get the same amount of precipitation is also higher–because if the cooler air was even close to the historic average low temperature, it would precipitate significantly more water (as rain or snow–depending on the temp at altitude AND near ground level). We see that here (MN) now. Winters are significantly warmer statewide–but snowfall varies wildly. 2022-2023 was the third-most precipitation year (snow AND rain) since records started being kept in the 1880s. Duluth set a new seasonal high-precipitation (rain and snow) total this past winter.

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So I did a little digging and found this study that shows a positive trend. Now I am confused.

Abstract Precipitation varies spatio-temporally in amount, intensity, and frequency. Although, much research has been conducted on analyzing precipitation patterns and variation at the global scale, trend types have still not received much attention. This study developed a new polynomial-based model for detecting nonlinear and linear trends in a satellite precipitation product (TRMM 3B43) for the 1998–2017 period at a near-global scale. We used an automated trend classification method that detects significant trends and classifies them into linear and nonlinear (cubic, quadratic, and concealed) trend types in satellite-based precipitation at near-global, continental, and climate zone scales. We found that 12.3% of pixel-based precipitation time series across the globe have significant trend at 0.05 significance level (50% positive and 50% negative trends). In all continents except Asia, decreasing trends were found to cover larger areas than corresponding increasing trends. Regarding climate zone and precipitation trend change, our results indicate that a linear trend is dominant in the warm temperate (77.7%) and equatorial climates (80.4%) while the least linear change was detected in the polar climate (68.9%). The combined results of continental and climate zone scales indicate significant increasing trends in Asia and arid climate over
the last 20 yr. Furthermore, positive trends were found to be more significant at the continental scale, particularly, in Asia relative to the climate zone scale. Linear change in precipitation (80%) was the most dominant trend observed as opposed to nonlinear (quadratic [11%] and cubic [9%]) trend types at the global scale.

So do you have a link to the study you quoted. I would like to beat them together in CHATGPT.


Here’s the Nguyen article, “Global Precipitation Trends across Spatial Scales Using Satellite Observations”

Yes (but not with a statistically significant acceleration). At the same time, surprisingly, global land area has increased.
The researchers analysed satellite images recorded by NASA’s Landsat satellites, which have observed the Earth for decades…

Coastal areas were also analysed, and to the scientists surprise, coastlines had gained more land - 33,700 sq km (13,000 sq miles) - than they had been lost to water (20,100 sq km or 7,800 sq miles). “We expected that the coast would start to retreat due to sea level rise, but the most surprising thing is that the coasts are growing all over the world,” said Dr Baart.


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Key point: Where are the gains AND are they habitable in the near future, or not? Risk?

I suppose this all fits into the discussion in a concurrent thread about ‘settled’ science. What is settled is that the earth is warming. What isn’t settled is
a) what does it mean?
b) what do we do about it?

What does it mean?
Clearly, as we can see upthread, it is not hard to find ‘dueling papers’. Sea level is rising, but some papers say land area is decreasing and others that it is not. Ditto on the precipitation papers.

Those islands in the Pacific that are said to be drowning; photographic studies show they now have greater area than they did during WW2. So, yes, the sea level is rising but there are other processes going on.

What do we do about it?
This is called climate policy and is not ‘settled’. Do we spend a trillion dollars for a temperature reduction of a few hundreds of a degree? Or do we spend money on adaptation?

And then, if you were king of these United States and had an extra $100 billion in your back pocket, would you spend it on a high speed train from San Francisco to LA or on a storm barrier to protect the New York/New Jersey bight area? Definitely not settled.

And then there is the international dimension. The growth in greenhouse gas emissions comes from the developing world (the US and Europe are declining).

Et cetera, et cetera et cetera.


If the atmosphere on average is capable of holding more water that doesn’t mean more rainfall. In some areas the conditions for rain will be made more difficult by rising temperatures, because temperatures are less likely to fall to the threshold required for precipitation. That suggests droughts. On the other hand, in areas where the conditions for rain are met, because the atmosphere is holding more water the chances of extreme precipitation increases.

The climate models to my knowledge do not consistently predict more global precipitation. What the great majority of them do agree on is that there will be an increase in extreme events that lead to flooding or droughts.

Increase in droughts due to climate change:

Increased risk of extreme rainfall events due to climate change:

Layperson description of what climate models say about precipitation:
Explainer: What climate models tell us about future rainfall - Carbon Brief.


@DrBob2 @btresist

I am definitely no expert here, but it’s fun to try to think this through in some kind of basic way.

Let’s suppose a warmer atmosphere with more capacity for water in the form of water vapor and a larger ocean with, of course, more water. Those are then larger quantities of water in storage, on average (averaging over a year, for example). Precipitation and evaporation are fluxes or flows of water between these two storage areas.

In a steady state model (with quantities of water fixed, on average, in the atmosphere and ocean), then with a warmer planet with a warmer atmosphere and warmer ocean (in the sense of the earth now instantly absorbing more energy from the sun), we would have more evaporation (a flux up to the atmosphere). On average over time, at approximate steady state, precipitation would equal evaporation and hence precipitation would increase along with the increase in evaporation.

However, suppose we are not in a steady state in two senses. First, the atmosphere and ocean are both accumulating more energy. And second, the quantity of water in the ocean is increasing (from melting ice). A larger and more-energy-absorbing ocean has more evaporation (and hence more precipitation), but a more-energy-absorbing (and warming) atmosphere can hold more water before it precipitates (thus lessening precipitation). And also, a larger ocean has more capacity to store energy and could potentially absorb more energy before evaporation occurs (and hence act against increasing precipitation). Further, if the pattern of mixing of the ocean surface with deeper ocean layers is increasing (no idea if this is actually happening), this could further increase the ocean’s capacity to store energy before evaporation occurs (and hence act against increasing precipitation).

It seems a steady state model might imply more precipitation as the earth retains more energy due to greenhouse gas effects, but with a non steady state model, maybe it depends and would take a long, long time to play out and also might be quite difficult to measure empirically. (although I feel like I have seen many headlines about how much more energy the ocean is storing)

I suppose there could be even further processes at play, such as a more windy atmosphere could increase evaporation from the ocean.

I’d be interested to hear ideas or data or models.


Here’s an example from UCAR:
" A warmer average global temperature will cause the water cycle to “speed up” due to a higher rate of evaporation. More water vapor in the atmosphere will lead to more precipitation. Global average precipitation can increase by 7% for each degree of warming, which means we are looking at a future with much more rain and snow…"
Predictions of Future Global Climate | Center for Science Education.

I came across a paper by Li that found different trends – a decreasing trend for the CMAP data, a flat trend for the GPCP data (as in the Nguyen article) and an increasing trend for the reanalysis data.


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With rising sea levels there can not be more rain fall.

The reason is somewhat basic. While meteors deliver a tad more water to the planet over time, water is also released from the atmosphere.

If we account for the amount of water on the planet as a zero sum game, then only so much rain can fall. The release of water from the glaciers is mostly raising the sea level.

The oceans are also the atmosphere.

I think you have it right. There are two problems with trying to project or detect a rising trend in precipitation. The first is that there is a chaotic element to weather, which increases with temperature. This means that it is very difficult to make projections of stuff like precipitation levels. Rising temperatures will increase the likelihood of precipitation but that trend will be obscured by the substantial year-to-year fluctuations. It may take a long time to see it even with good data.

This leads us to the second issue. The linked study only provides about 30 years of satellite data and does not include precipitation measurements beyond 60 degrees N and S. The latter is unfortunate as the most significant impacts of climate change so far has been happening at the poles. We simply don’t have good enough data to make any sort of conclusion about precipitation levels other than that of the study, which is that there is no evidence of an increase in precipitation between 60N and 60S during the past 30 years.

In contrast, the frequency of severe events like droughts and extreme precipitation appears to be less impacted by other factors. There the models are capable of making consistent projections that so far are in line with observations.

From link:

“The take-home message from our study using the new 33+ years of high-resolution global precipitation dataset is that there seems not to be any detectable and significant positive trends in the amount of global precipitation due to the now well-established increasing global temperature. While there are regional trends, there is no evidence of increase in precipitation at the global scale in response to the observed global warming. Perhaps the explanation can be that satellite data used in this study is limited to between 60°N and 60°S and any precipitation above and below these latitudes is unavailable.”

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The IPCC (AR6, Chapter 8, Water Cycle Changes) says

The human influence on the global water cycle is often summarized as an intensification or an overall strengthening which has been observed since at least 1980 (high confidence)

Although an increase in global precipitation is consistent with physical expectations, it has not yet been detected and attributed to human activities given large observational uncertainties and low signal-to-noise ratio .

Other metrics are more suitable to detect and attribute changes in the global water cycle, including the likely increase in global land precipitation since 1950 which is likely due to a human influence.

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The deeper ocean areas are also warming, which was not understood until a few years ago. It is the reason the temps worldwide did not increase as fast as expected for a while. The deep oceans were NOT analyzed for heat gain until recently–then it was learned they had also warmed.

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I wonder if we can suck the heat out of there quick enough to make a difference? If we use the excess ocean heat produce energy, and the remaining excess heat from that energy production and use can be soaked up by the ocean again, then we might create a virtuous cycle of less harmful energy usage.

It should be noted that the areas north and south of 60° only make up 13% of the globe. More importantly, there is (relatively speaking) very little precipitation in the polar regions. Antarctica, in particular, is a very cold desert.

Adler et al. extended the satellite-based GPCP data by using “precipitation estimates from temperature–moisture sounders”. They also found no significant global trend.


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Okay, maybe we have a consensus.


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