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This question is similar to What would happen if there was no wind?, but the lack of wind is confined to a small portion of the planet. To make things concrete, the affected region is roughly circular with a radius of about 150 km. The entire region is affected by magic that causes the wind outside to flow around the edges of the circle as if the whole area were covered by a glass dome.

To make things concrete, here are the details on the affected region:

  • It's roughly circular, with a radius of about 150 km.
  • Magic causes the wind from outside to flow around the edges of the circle, more or less as if the whole area were covered by a glass dome.
  • The clouds follow the path of the wind, so there's no rain and the skies are perpetually clear (which also means the area around the perimeter gets more rain than it normally would).
  • The terrain is plains and rolling hills, with rivers flowing in from outside the affected region.

The question is, do the rivers and other processes distribute enough water throughout the area to prevent most of it from becoming a desert in the absence of wind and rain? Or are we inevitably left with small fertile areas around the rivers and desert everywhere else? I was specifically envisioning the area as a place for small nomadic hunter-gatherer societies, so it wouldn't need to support agriculture, irrigation, etc.

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    $\begingroup$ Does the barrier only stop wind? What about clouds which may be travelling with the wind? Clouds and Rain distribute water, so without them you will have issues keeping things green unless there is plenty of water in the ground. $\endgroup$ – Shadowzee May 28 at 3:04
  • $\begingroup$ @Shadowzee It's not a physical barrier - the notion of a glass dome covering the region was simply a metaphor to help explain the situation. The clouds follow the path of the wind, so there's no rain and the whole region has perpetually clear skies. I've edited the question to clarify this. $\endgroup$ – Ben S. May 28 at 3:16
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    $\begingroup$ A area 150 km wide with plains, rolling hills and a river will most certainly create its own winds... In fact, an area 150 meters wide with uneven elevation will create its own air currents, because of uneven insolation. $\endgroup$ – AlexP May 28 at 8:27
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    $\begingroup$ Clarify please: granted that there is no wind; what happens when water vaopour rises from the surface of the rivers & surrounds and into the air? There's no breeze to carry it away. Won't this land be perpetually foggy a/o cloudy? $\endgroup$ – elemtilas May 28 at 18:53
  • $\begingroup$ @elemtilas Good point, I hadn't considered that. I may ask another question later based on this, but for this question, let's assume that the magic pulls the water vapor into the area outside of the affected region. $\endgroup$ – Ben S. May 28 at 21:16
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They will not need to be very nomadic.

This aside from the fact that 150 km is not very big. Life in your magic circle will be next to the river. As an example here is the Amu Darya between Turkmenistan and Uzbekistan.

Amu Darya

Life is clustered by the river because there is no rain in the desert. In your windless land there will be no rain and it will look like this. Your nomads can go up and down the river hunting and fishing. Or stay in one place near the river - they can use the river for irrigating crops and make fish pens.

Another difference is that all plants will be insect pollinated. Those plants will not get competition from wind pollinated plants (like grasses) and so will do great. Some wind pollinated plants might be able to use the river to carry seeds and so colonize the area from upriver.

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  • $\begingroup$ The Nile is another example of a water-rich area (in the Nile Delta in particular) where there is actually a fair bit of humidity in the air, yet there is almost zero rainfall. $\endgroup$ – Cyn May 28 at 16:14
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    $\begingroup$ Just to be clear, you're saying that the land will become a desert, but it could still support life as long as the people lived near the rivers. If I wanted something that wasn't mostly desert, I'd need to alter the parameters somehow. $\endgroup$ – Ben S. May 28 at 18:41
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    $\begingroup$ @BenS. consider somewhere which is a river delta, or perhaps a lot of natural springs forming many oases. $\endgroup$ – Starfish Prime May 28 at 19:48
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I believe the nomadic society could survive, but further details may need to be addressed to determine their approach.

  1. Can clouds pass over the dome?

    If they can, at what altitude? The type of cloud could impact what types of weather and albedo.

  2. How exactly is water vapor dispelled?

    If water vapor is pulled from the area rather than vanishing, this would probably cause more clouds, high humidity, and rain. If this pull is not instantaneous, this could cause some sort of humidity gradient, with the driest point being the origin.

  3. Can it rain in or above the area?

    If the rain can indeed fall through the dome, the increased water vapor and new cloud routes may maintain the humidity, or even over saturate the area.

  4. How does erosion and weathering play?

    The interior of the dome would lack signs of wind erosion and weathering. If rain precipitated down the sides of the dome, the edges would show greater signs of water erosion and weathering.

  5. How would technology complement a nomadic lifestyle?

    If rain is sparse within the area, they could create water basins on border. This would give them intensive to travel from each basin rather than settling down around a river.

    They may consider ditches or primitive types of piping, such as bamboo. This irrigation wouldn't necessarily be agriculturally focused, as it's not for the propagation of crops, but rather the maintenance of land and ecology dependent on the water. Aesthetically these ditches could double as religious or culturally relevant symbolism (such as the Nazca Lines).

  6. Is animal ecology and evolution considered?

    What are the new niches to fill, and how are they resolved? Do animals start retaining more water? Do they utilize primitive fans to maintain wind-based plant pollination? Do plants adapt their seeds to be sticky, adhering to hairy animals to either be displaced elsewhere or begin some sort of symbiosis?

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    $\begingroup$ My plan was that the imaginary dome would extend above the cloud layer, so that rain couldn't form above it and fall through. That said, rain clouds apparently go a lot higher than I'd thought (nationalgeographic.org/encyclopedia/cloud), so I may need to rethink that. $\endgroup$ – Ben S. May 31 at 3:59
  • $\begingroup$ If your intention is to deny any clouds over the entire area, you may consider referencing the area as a cylindar or circle rather than dome. I may be in the minority, but I interpret those geometries to effect clouds very differently. Thanks for the reply, I'm glad I could spark some thought. $\endgroup$ – Tristong May 31 at 14:21
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I think without any wind to bring in moisture, and no rain falling, you will only get a desert area with rivers running into, as suggested by Willk.

There is a good example of a group of people living in a desert who follow a nomadic hunter/gatherer lifestyle, the Khoi-San of Southern Africa. Even to this day they remain in the Kalahari desert and continue their nomadic cultural way of life.

As another idea for a group living in a desert type biome, you could have them be herdsmen like a lot of the indigenous tribes of Southern Africa. With a large enough herd of animals to sustain the group of people, grazing will easily become a problem if there is only vegetation along the banks of the rivers, so it would be beneficial to rather be nomadic, and move along the river with your herd once the grazing starts to disappear.

Bonus is that as a river has two banks, for half the year they can move down one side of the river, then cross it at a narrow/shallow point, and move back up in the opposite direction, allowing enough time for the vegetation to recover.

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If the 150km circle is at the bottom of a crater with gentle walls climbing up on all sides and if the intensified rainfall just outside the circle slides off those walls and flows down towards the center, then the enclosed area could be anything from a desert to a swamp to a lake depending on how much rainfall naturally occurs in the area.

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