Chinese and other overseas investors own those US desert farms. They were attracted here by the massively generous water rights they get automagically.

ref: https://grist.org/agriculture/u-s-southwest-already-parched-...

While the US is unlikely to mess with the private property rights, export restrictions are easy to change.

Damn I want a dessert farm

I want to visit the Maybel Syrup Dessert Farm

Very little of the water used to grow hay and alfalfa actually ends up in the hay and alfalfa to be exported. Most of the water ends up in the atmosphere via evapotranspiration.

The amount exported is something like 0.005% of the evapotranspiration amount.

Here are some numbers [1] for Idaho crops. There might be some differences in Utah but they should be in the same ballpark.

> Not much water is exported with alfalfa hay. Potential irrigated alfalfa hay yield at elevations near 4000 feet is about 7.5 tons/acre. Hay harvested at 12% moisture removes 240 lbs water/ton hay, or 1,800 lbs/acre for a normal crop of alfalfa hay per year.

> Evapotranspiration (ET) is the primary use of water by alfalfa and averages about 36 inches/year (900 mm) at Kimberly. The ET at peak periods of 0.4 inches/day (10 mm/day) can reach 4080 tons of water per acre and 45 tons per acre per day.

[1] https://www.uidaho.edu/-/media/UIdaho-Responsive/Files/cals/...

The opportunity cost is there, whether the actual water is exported or not. Especially if the local resource is somehow subsidized either directly or indirectly.