|Source: Tinelot Wittermans via Wikipedia|
Weather modification is the term given to the alteration of weather by humans. It can be intentional (e.g., cloud seeding) or inadvertent (e.g., effects of aerosols and land-use changes on precipitation).
We are doing both today. Cloud seeding is intentional, but it really isn't really all that well understood how it works in nature and what the unintended consequences might be. Modification of local meteorology by cities, especially large ones, is inadvertent but has a robust and clear signal through the urban heat island and changes in precipitation patterns. Of course we are also running the ultimate inadvertent weather modification experiment by jacking up long-lived greenhouse gas concentrations and then seeing what happens.
The efficacy and ethics of weather modification has long been a point of debate in my field (see American Meteorological Society information statements Inadvertent Weather Modification and Planned Weather Modification through Cloud Seeding). The use of weather modification during warfare, something that the United States did in southeast Asia during the Vietnam war (e.g., Operation Popeye), has been banned by the United Nations.
Perhaps the UAE would be willing to negotiate with California for the Sierra Nevada. That would be a win for them and a win for Utah since the moisture flux into the Great Basin would be much higher if that high barrier wasn't upstream. Calling Kennecott?