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Picture, in a near future, that we build cities vertically rather than horizontally. Need a new city block? Add another few floors. Disregard for the moment any physical construction problems this may present.

My question pertains to the effects that such a city would have on the climate and weather in the immediate area. Would there be any changes to cloud formation, rain fall, wind patterns, etc? Would there be any changes at all? I'm interested in effects for people at all levels of the city, including top, middle, and ground level.

Assume that emissions are more or less the same as they are now.

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    $\begingroup$ How high is the top? $\endgroup$ – Vincent Sep 9 '15 at 4:32
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    $\begingroup$ Well we can build 1km structures right now, so it's reasonable to assume that in "near future" buildings could be 5km-10km $\endgroup$ – Freedo Sep 9 '15 at 5:09
  • $\begingroup$ Interesting question! Vertical cities are a staple of futurology and there are some incredible concepts out there, but this is the first time I've seen it approached from this angle! $\endgroup$ – Whelkaholism Sep 9 '15 at 9:16
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    $\begingroup$ I can't find my answer, but at one point I put forth an answer on a related question: some of the taller buildings, like the ones NASA has for final assembly of the shuttle, are large enough to actually have their own internal weather patterns due to temperature and relative humidity. On high humidity days, those buildings have rain inside them. $\endgroup$ – Cort Ammon Sep 9 '15 at 21:08
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    $\begingroup$ @TommyMyron No but very close, Burj Khalifa with 829m at the cost of only 1.5 billion dollars and 5 years of construction. And its height is not limited by our tech but by cost and will, right now there is not any race to build the highest building in the world, but if we wanted so we could build a 1km structure right now, there's just no reason to build that other than break mundial height records. But soon with our population reaching 10 billions of humans and everybody wanting to live in the cities its reasonable to expect a 2km+ buildings at near 2050. $\endgroup$ – Freedo Sep 10 '15 at 5:38
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There are really too many variables to give a real answer, but I can give a suggestion that, I hope, has almost the same practical value. Treat a building as mountain of the same height, a city as a mountain range. That should give you lots of real world models that would be somewhat credible. In reality it of course depends on what the buildings are made of, how the air conditioning is handled,the exact geometry of the building andthe surrounding terrain and so on, but IMHO you can presume the designers would have "played it safe" to avoid unseen complications.

Addition:

Since both Vincent and Spacemonkey mentioned the wind accelerating between the buildings... This is true, but somewhat or, really, grossly misleading. The buildings actually impose significant drag on the wind, so while the wind between the buildings may be accelerated, overall the effect will be dominated by wind decelerating both ahead and behind the buildings. Mostly behind. Obviously this is all dependent on the geometry chosen. But in all cases wind will lose energy to drag, the only question is how much.

Actually, if I was building megabuildings, I would use the effects they have on local winds to concentrate wind power... Which would increase drag.

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  • $\begingroup$ Can I assume that cloud formations and wind patterns would at least be broken up by the towers, if not blocked completely? $\endgroup$ – Thomas Myron Sep 9 '15 at 14:47
  • $\begingroup$ A tower or small group of towers would create turbulence with clouds "flowing around" them. A large city might be able to break or block weather. Like I said, it should work pretty much like a mountain area of same height and area. Different geometry limits similarity for single towers or small groups, but given how large most weather is it shouldn't make that much of a difference. There should be a rain shadow and obviously a wind cover, if that is what you are asking. $\endgroup$ – Ville Niemi Sep 9 '15 at 15:33
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Your city would not block the winds, unless the buildings are really packed close together like a wall. The winds should move between the buildings causing turbulence (hopefully, the engineers built them to resist this). The winds would accelerate but will decelerate once they leave the city.

I believe the clouds will form as they would do normally, unless your buildings are generating heat. If that is the case, it would generate small clouds or fog.

I'm not really good with cloud physics but it seems like most rainy clouds would form under 10km. The lower level will have the most precipitation. Mid level (2000-5000m) will have plenty of rain too but those above will not have that much. Not only the top (above 5km or 6km) will be dry but the temperatures are likely to always be under the freezing point. If you want to know what will be the temperature at a certain latitude: usually, it decreases by 6.5°C for every 1000m. Actually it's 5°C if the air is humid and almost 10°C if the air is really dry.

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  • $\begingroup$ "Mid level (2000-5000m) will have plenty of rain too but those above will not have that much." Does this mean the higher levels would be above the general cloud level? Or would rain simply fall as snow at those levels? $\endgroup$ – Thomas Myron Sep 9 '15 at 21:18
  • $\begingroup$ @TommyMyron Normally, the rain occurs as the air rises and cool off. Most of the water contained in the atmosphere doesn't reach that high. it's not completely dry above that but it's much less. Actually, some high altitude clouds might trigger rain but the water will evaporate before reaching the ground. $\endgroup$ – Vincent Sep 9 '15 at 21:38
  • $\begingroup$ So... the clouds would be below the higher levels then, yes? :) $\endgroup$ – Thomas Myron Sep 9 '15 at 21:44
  • $\begingroup$ @TommyMyron Most of them yes. $\endgroup$ – Vincent Sep 9 '15 at 23:12
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Love the question!

The weather aspect is probably the one I'm least sure off. Like Vincent stated, I'm pretty sure not much would change unless the buildings are fairly compact.

1) I'm taking Montreal as an example here (so it might not be the best example):: Take your current city downtown areas, it may not look like it necessarily from the ground floor, but buildings really aren't that close together. In the few areas that they are, also like Vincent stated, wind accelerates because of the lack of space. I imagine in your future city, buildings WILL be close together so that's definitely something to take into account (for any balconies etc...)

2) If your buildings aren't all the same height (with 1km+ buildings I'm guess the variety in height may possibly be increased, with some buildings being 500m tall, others 1200 etc...) and even without the height variety, on a building that is over a km tall, all the ventilation and heating waste etc.. might not all be possible to dump outside the building from its top like current skyscrapers generally are. If you have 30% of your city that dumps out water vapor and heat at around 500m, and 30% of your city is over 600m etc... than I can see that creating different levels of micro climates inside the city itself. (Again assuming the city's building are tightly grouped), the lower ground having lower mercury index temperatures but less wind (resulting in perceived higher temperatures?), the middle having lower temperature and lower perceived temperature because of the wind chill, and the higher portion having higher humidity, temperature and wind factor.

3) Not in link with the weather directly. But don't forget the underground part of your city. Again I'll use Montreal as an example. The entire downtown is linked by underground complexes with multiple sub levels, being malls, transit lines, parking lots, food courts, utility services, etc... And those areas also kind of have their own 'weather'. In a futuristic city of your scope, I can imagine we'd be talking even more sub levels (5-10+?) which would impact the overall city even more.

EDIT: I did a bit of googling and thinking and buildings wouldn't just get taller, they'd also get bigger. So I think this would again probably lessen the climate changes (exterior weather). However with larger buildings of extreme heights, my guess is you'd end up with arcology type buildings, each one aiming to be as self-sufficient as possible. (Imagine you have 300 floors, how long it would take to get food at lunch, or the transit time it adds to go home etc...) Many Sci-Fi have such buildings - the most visual example I can think of (not the best but most visual) is the 'District' buildings in the Judge Dredd remake.

Which brings me to answer. The exterior weather would not be noticeably affected. However you'd have 'weather' inside your buildings - in direct reaction to the outside weather as well as anything going on inside. (Anyone who's worked in a large building knows how the heating/humidity/cooling systems can be fickle and temperamental - at least the one where I work is. The bigger the area to regulate, the more it'll be. Etc...)

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