Has climate change changed rain?

Submitted by wjd03 t3_zihh24 in askscience

I had the thought today that rain is one of the last things in the world that feels untouched by humanity. Water droplets have always fallen from the sky. But has the way they fall changed? Do we know if raindrops are bigger or smaller nowadays? Or if they fall faster than they used to? I know the amount of rain in an area can change quickly as I’ve witnessed it myself but I wonder if rain has changed in any other ways?

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Maxo11x t1_izs93tc wrote

Rain droplets themselves I don't know if the average size has changed, but I know that they have become more acidic due to increased sulfur and carbon dioxide in the atmosphere getting absorbed into the clouds. Also humans have changed the weather patterns and climate, changing the humidity in areas, with sometimes odd effects. Some areas are getting more and more rainfall with others recieving less due to changing climate tendancies.

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PerspectivePure2169 t1_izsq0r7 wrote

This is partially true. In recent years rain has become significantly less acidic, because the biggest contributor was sulfur from burning coal, and that's been reduced thru stack scrubbing and general replacement of coal.

It's not a minor effect. Sulfur is a necessary nutrient in plant growth, and quite a few farms that traditionally benefited from the contribution of acid rain now have to add it when fertilizing.

There was always a localized effect to it though. The UK had and has major problems with loss of peat in high moorland because of the steady deposition of acid rain on thin soils under a constant wind pattern. That land can only sustain peat and without it is subject to erosion.

For deeper soils on cropped agricultural land it's of benefit.

CO2 isn't nearly as significant at creating acid rain, since sulfuric acid is far more powerful than carbonic.

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NDaveT t1_izu9qit wrote

Yep, acid rain is an example of scientists noticing a problem and coming up with possible solutions, and policymakers implementing and enforcing some of those solutions.

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memeyboi420 t1_izswz61 wrote

Rain can be affected by aerosols and fossil fuels

Fossil fuels release toxic chemicals into the atmosphere that can react with other atmospheric molecules to form acids. These acids fall down with precipitation to cause acid rain.

To answer your question about raindrop size, aerosols should be examined. Aerosols are basically just very small particles that tend to float into the air. Once in the air, water more easily collects onto the particles, which results in more, but smaller, water droplets. This doesn’t necessarily mean all water droplets are smaller now when compared to a century ago, but it’s safe to say that areas with more aerosol emissions (like cities) will have smaller but more numerous raindrops.

I hope this somewhat answers your question

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Indemnity4 t1_izvb6v4 wrote

> Do we know if raindrops are bigger or smaller nowadays? Or if they fall faster than they used to?

Really fun deep dive into atmospheric sciences.

The main effects on rain drop size are air temperature, water drop temperature, air density and atmospheric pressure. None of those are hugely variable due to climate change compared to natural cycles.

Air pollution has a much more dramatic effect on raindrops than does atmospheric CO2 levels. Atmospheric dust or diesel fuel emissions from cars have huge effects; atmospheric CO2 not so much.

At a simple level, there is no historical change. An individual rain drop is the same size and falls at the same rate it always has, which is the terminal velocity for that droplet. It fits into a distribution range of sizes called the Marshall–Palmer distribution.

Rain drop size (and subsequent speed) naturally vary with the seasons and where exactly it is raining. For instance, rain over the oceans is smaller droplets at slower speed, whereas rain over land is bigger droplets at faster speed.

Air pollution affect example: an area may have a lot of atmospheric dust/pollution that forces a lot of smaller droplets or drizzle (e.g. London fog from period dramas). Remove that air pollution and the rain drop size and speed will change to larger drops / faster speed (e.g. there is no more soupy London fog once the coal fired power stations closed/cleaned their emissions.)

Global changes to rainfall patterns due to climate change get too long for a simple post. But the actual rain drops themselves are relatively stable and predictable.

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[deleted] t1_izsckqi wrote

Not sure about the size of the raindrops themselves having changed, but the rain that falls in general is far more acidic than it ever used to be. I’m pretty sure I read recently in a science article that there’s literally not one place left on earth where it’s safe to drink the rain water.

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