# Meteorological consequences of walls reaching into the sky, enclosing a large area

Suppose we walled off a 1000 km square. These walls would be made of unobtanium (so they don't break), and have no cracks or holes that go all the way through. They are also around 15 kilometres high, to stop birds flying over. No living thing can cross the walls.

This is a major element of my setting. This is definitely not a realistic option for enclosing a geographical area, but it has plot reasons.

However, something this big would have major meteorological consequences. Even a measly 2 kilometer high mountain range makes a huge rain shadow. This thing is quite definitely high enough to prevent some (if not all) clouds from crossing over it.

Basically, I have no idea what this would do to the weather of the area. Assume that the wall went up over the course of a year, and that the area enclosed... For simplicity's sake (as in, I don't have to provide a completely made-up map), let's centre this square on Italy, and keep the walls aligned to the compass. Rome to be precise. If the thing is to big to have an actual square, the corners should have right angles, and the distances form the walls that are opposite each other should be 1000 km measured from the middle to the middle. The wall would not be transparent For thermal stuff, let's say it has the characteristics of a hundred meter thick wall of limestone.

My question is, what would this do to the weather inside, and outside the walls? Could people live inside the enclosed area, or would it quickly become a barren wasteland? If it would become a wasteland, what could I do to keep the walls, but avoid this scenario?

• The area of Europe is estimated at 10.18 million km², that's a lot more than 1000 km square (1,000,000 km²). Which one do you want us to think about? Apr 24, 2020 at 10:39
• @mwarren The square. I had a look the other day, and it seemed like the square would cover a large chunk (50-80%) of Europe, which is why I wrote that. I'll get rid of that geographical reference. Apr 24, 2020 at 10:42
• Thanks for the edit. I'm not a weather expert so I won't make an answer of this, but I would be concerned about loss of wind. The jetstream apparently only goes up to 15 km and I don't know if sufficient pressure differences within the square would cause internal winds. Apr 24, 2020 at 10:57
• (1) A square with a side of 1000 km has an area of 1,000,000 square kilometers. A square with an area of 1000 square kilometers has a side of about 32 km. (2) Rome is 25 km (16 miles) from the sea. (3) Italy is generally less than 200 km (125 miles) wide. (3) Unless a large part of the enclosed area is a sea, what you will get is an extremely dry desert. Water vapor is lighter than air, and will escape; rain clouds are much lower than 15 km, and won't come in. (4) A square with a side of 1000 km centered on Rome will include Nice (France), Sarajevo (Bosnia) and Zagreb (Croatia). Apr 24, 2020 at 12:04
• One imagines these walls also sever seas and rivers? That water cannot flow beneath the wall? Apr 24, 2020 at 13:56