1.?Background . The semi-arid Southwest US (SWUS) has been experiencing persistent drought conditions since the turn of the century, highlighting the need for long-term climate prediction to aid water management and planning. The region is approaching the limits of water resource use with adverse implications for social, economic, and ecosystem sustainability, compounded by population growth and attendant increase in demand (Scanlon et al2005 , Meehl et al2007 , Zhang et al20...