I have planted a bunch of trees that I will be pollarding but for livestock fodder, fuel, and mulch.
I suppose pollarding might reduce water consumption, but trees also produce water for an area through several means such as condensation. Trees will help dry out wet areas but I don't think they dry out soil that has a proper amount of moisture.
There are lots of good reasons to coppice but I haven't read that reducing water needs is one. I do know that coppicing favors leaf growth over woody growth & leaf growth
might need more water, not sure.
Also, it seems that you're more likely to need to irrigate the trees when planting out. By the time you're ready to coppice, their
roots might be so deep that you wouldn't have to irrigate anyway. Put in some swales to eliminate the need for irrigation and plant on the swale mount.