That data pretty well exists, though it could always be improved. There are charts you can find that give the annual water usage per tree for different varietie

That data pretty well exists, though it could always be improved. There are charts you can find that give the annual water usage per tree for different varieties of trees. But, as much as I'm a complete raving lunatic fan of data-driven politics, there's still politics involved. The data doesn't really tell you what to do, which was jcranmer's point, and mine. At best it just tells you what not to do.