I would distinguish terraforming from irrigation. It sounds like you are talking about setting up a self-contained system to irrigate the land every year, whereas I would restrict terraforming to a permanent climate change, so that it rains and desalination is no longer necessary. This is what people mean when they talk about terraforming the Sahara. The desert was green five thousand years ago when the pyramids were built, so it probably has multiple equilibrium climates and a sufficient intervention could get it to jump to the other. I don’t know how plausible this is for other deserts. The idea is to irrigate a bounded number of times to grow appropriate trees to trap water.
A permanent change could be much cheaper per acre because the solar panels and desalination plant can be reused for new parcels. The downside is that this probably has large gains from scale: air flows freely between neighboring parcels and thus humidity is an externality. Whereas the whole point of a self-contained system is that you can start small.
I would distinguish terraforming from irrigation. It sounds like you are talking about setting up a self-contained system to irrigate the land every year, whereas I would restrict terraforming to a permanent climate change, so that it rains and desalination is no longer necessary. This is what people mean when they talk about terraforming the Sahara. The desert was green five thousand years ago when the pyramids were built, so it probably has multiple equilibrium climates and a sufficient intervention could get it to jump to the other. I don’t know how plausible this is for other deserts. The idea is to irrigate a bounded number of times to grow appropriate trees to trap water.
A permanent change could be much cheaper per acre because the solar panels and desalination plant can be reused for new parcels. The downside is that this probably has large gains from scale: air flows freely between neighboring parcels and thus humidity is an externality. Whereas the whole point of a self-contained system is that you can start small.