We can even estimate the temperature of the water being used, in general, for irrigation purposes, as well as how much of it is sprayed and so forth, and it turns into a simple mathematical exercise.
Irrigation could very well increase the amount of water evaporated into the air several percentage points.
So, you're the smart guy, give us the answers on this one.
Simple.
Belief in global-warming is faith-based science.
People who believe it don't need any facts, just the love and support of their fellow global-warming zealouts.
The short answer is that in irrigation (the part of it the works and isn't wasted) the water soaks into the ground and some of it is taken up by plants whereas over large open bodies of water there's nothing to slow it down.
Example: two thirds of the precipitation that falls east of the Rockies, comes from the Gulf of Mexico. It's a little over 66%.
Irrigation water evaporation on the other hand, has yet to reach the tenth of one percent range. It has about as much impact as an extra quart of water going over Niagara Falls.
We can even estimate the temperature of the water being used, in general, for irrigation purposes, as well as how much of it is sprayed and so forth, and it turns into a simple mathematical exercise.
It is definitely not as simple as that. You don't take into account the ambient air temperature, the dew point (which effects how much can be evaporated), how much of it is absorbed by the soil, winds, which can change the whole equation, the amount of insolation (sunlight) and dozens of other factors it would take too long to list.
If weather/climate research were as simple as you make it our to be, we'd already have our forecast for Easter 2020.