One day humans might be competing with trees for water:
It is likely that the northern Great Plains will become
hotter, which will increase evaporation rates and result in drier conditions. It is also likely there will be more extreme weather events, such as longer and more-intense droughts that could lead to new Dust Bowls or more intense rain events that increase the potential for erosion. Projected vegetation shifts such as the expansion of eastern deciduous forests westward and the increase in woody life forms in the Great Plains depend on the effect of increased atmospheric CO2 concentration that would enhance the water-use capacity of trees, which could mitigate drought stress. Unlike grasses, deeper-rooted trees under drought conditions would also depend for their survival on the persistence of the deep aquifer, which would be even more severely taxed by human activities in the region as rainfall becomes scarce.  [emphasis mine]
1. Wiens, J. A. & Bachelet, D. Matching the multiple scales of conservation with the multiple scales of climate change. Conservation biology 24, 51–62 (2010).