Trees actually roughly double the amount of rain a given area recieves and draw it inland. This is called the biotic pump.
Fresh water -- water usable for irrigating crops, drinking, bathing, etc. -- is a shockingly tiny percentage of the water on planet Earth. From the USGS:
96.54 percent of Earth's water is salt water in oceans and seas.
1.74 percent is locked up in glaciers and ice caps.
1.69 percent is ground water.
That's 99.97 percent of all water on the planet. Lakes, rivers and atmospheric moisture are a tiny percentage of one percent
This is why "our next wars will be fought over water." It also means thatits possible that planting more trees can actually increase the amount of fresh water without the problematic side effects you see from desalinization plants (such as waste heat).
It needs research but this possibly genuinely solves a lot of problems without disruptive and problematic ecological impacts. It isn't going to drain our oceans to double the amount of rain in arid areas by planting trees.
And it sidesteps our current idiotic mental model that we can either raise our standard of living by consuming more or save the environment and planet. It's idiotic because ruining the environment harms quality of life and undermines long-term economic stability and productivity.
So successful tree planting programs in arid areas plus wetlands restoration would go a long ways towards fixing a lot of "unfixable" problems. It even potentially calms things down in wartorn areas, many of which are deserts currently.
And maybe this is why the Hanging Gardens of Babylon were so extremely famous that everyone knows that phrase without really knowing anything else about the place. It was a desert city with lush growth of plants and it impressed the hell out of the world and went down in history for that accomplishment.
Perhaps at the time no one felt you needed to explain that it meant you had food security and it mitigated the hit, dry climate, so it was an issue if peaceful civilization in a harsh environment.
Historically, garden was probably interpreted as vegetable garden by default, not pretty plants in the yard of wealthy people who buy all their food elsewhere. And historically most people worked outside, usually in agriculture in some capacity.
This gave everyone an awareness of their relationship to the natural environment and passive solar with daylighting was the default norm for all buildings without anyone using those terms. It's a cultural wisdom we've forgotten and now the world does idiotic things like build Western style buildings in India, thereby making the heat worse.
I have described Fresno County California as a modern Hanging Gardens of Babylon that no one is paying any attention. They built canals to divert river water and turned a desert into a much more lush place with a lot of agriculture.
Fresno County gets just 11 inches of rain. Diverting river water to agriculture via canals is the story behind the birth of civilization in The Cradle of Civilization, which also was an area with rivers running through a desert.
Historically, the civilization in The Cradle of Civilization rose and fell repeatedly as competent human bureaucracy developed to manage water distribution went through cycles of gaining and losing competence.
Most likely, they got fat and happy, lost sight of the fact that this area doesn't work AT ALL if the canals don't work and maybe began worrying about lining their pockets as individuals or stopped wanting to do the gard, unpleasant parts of the job. Then things fell apart, times were hard and the next generation decided once again that the hard parts of running the canals properly fit the greater good was less of a hardship than not having them.
Rinse and repeat as a new generation takes their prosperity for granted and loses sight of what it takes to be prosperous in that area.
I think tree urinals are a good way to START the process of spreading trees to arid, distressed areas because if you are getting enough food and water to not die, you can afford this type of development. But someone would need to work out what happens next when people get fat and happy, think they deserve real bathrooms and shouldn't have to keep peeing on trees and like India "upgrading" to Western architecture, they begin destroying the whole thing by modernizing.