Calculating how much water is needed is the easy part, that's not the challenge. What I'm saying is that you can not use drip line to water the forests of the west. A computer model will not help you physically run drip line across an area that is so vast, the plastic alone would make it an environmental disaster, not to mention the CO2 produced to pump that volume of water over that much land, even if it were possible which it's not.
After the disaster that occurred in Paradise California
https://www.pbs.org/wgbh/frontline/article/camp-fire-by-the-numbers/where 85 people lost their lives, President Trump visited the area where he then referred to the town as "pleasure" instead of Paradise,(I mean 85 people were burned alive there, why bother getting the name correct right?) and said that we need to "rake the forest", "like Finland". This comment was met with disbelief and general mockery from Americans and Fins, as well as confusing the president of Finland as they do not rake their forests.
Now to be fair, leaves, needles, and general forest duff is very flammable, and raking it up and disposing of it eliminates that potential for fire danger in the area that it has been raked from, we should all be raking around our properties, but the reason Trump's comments were mocked is that his comments were completely tone-deaf due to a total lack of understanding of the vastness of the area he was proposing should be raked. It's simply not possible to rake the west, it's way, way, too big.
Proposing to water the forest is, in a similar vein, tone-deaf. It is not possible, computer modeling has nothing to do with the non-viability of this idea.
Sorry(truly) not trying to compare your ideas with Trump in any way, just an interesting example of when someone has an idea based on a good concept but not enough info to know that it is literally not possible to apply this concept in actionable form.