n the next 40 y, the number of urban dwellers in the developing
world is forecast to grow by nearly 3 billion (1). While this urban
demographic transformation is unfolding, climate change is
expected to affect the global hydrologic cycle. Anthropogenic
emissions of greenhouse gases will likely raise average global
temperatures, with temperature changes expected to be greater
nearthepolesthantheequator.Climatechangewillalsolikelyalter
precipitation patterns,withsomeareas becomingwetterand others
becoming drier (2). For some regions, climate and demographic
trends will present a fundamental challenge: how will water be
provided on a sustainable basis for all those new urbanites