What are the important factor(s) in maintaining the sustainability and adaption of the water resources within the watershed?

This is Peter Petersen.  I am currently writing a manual on the impact of the climate change on the hydrological cycle. One of topics is dealing with what do the water treatment operators and water resources managers need to know about the things that impact their watersheds in terms of sustainability and adaption particularly when they are experiencing an increase flux of people moving into their watersheds, like one example is the southwestern region of USA. I would appreciate any assistance that you might have. Thanks.