So a rainforest creates a positive feedback loop—vegetation creates evapotranspiration which encourages rainfall, which in turns encourages more vegetation.
If you wanted to badly enough, could you irrigate an area of land with enough water to produce vegetation, so that the vegetation created a similar positive feedback loop? Could you reforest or de-desertify areas of Earth this way? If so, how large would the area of land need to be before it could change the climate? Would you need the land area to be in a specific location? Like, would the new forest have to be in an area where it could generate rain more readily, or could rain be encouraged wherever? Would you need to do things other than just import water to do this, and would the forest eventually no longer need irrigation?
What other repercussions would result? For example, surely if you forested too much of Earth, you would cause drastic changes to the climate.
Main question: could you irrigate an area of land to create a forest which encouraged enough rainfall so that, eventually, you need not water it anymore, in an area where a forest did not previously exist?
I've toyed with the idea of an advanced civilization, having run out of other convenient sources of water, turned to desalinating seawater. If a civilization or nation relied on desalination for their freshwater, they would need large networks to take water from coastal areas inland. Such a network could provide the water in this question, if no other sufficient source was available.
Apologies for the broadness of this post. Many other questions are related to it, and I was seeking ideas for those related questions as well as the main one.