ABSTRACT
Understanding of the desert hydrologic cycle begins with a recognition of climate and the influence of climate variability on surface water and groundwater. Most towns and cities in the desert Southwest do not use significant surface water for domestic or municipal supplies. Influent stream reaches can also be considered a source of recharge, although a mass balance would likely indicate that the net change water available to an alluvial aquifer traversed by a stream is negative when both influent and effluent reaches and use by riparian vegetation is considered. In states such as Arizona and California, surface water and groundwater are considered legally to be distinct entities despite the hydrologic fact that they are intimately linked. Colorado River water delivered in CAP canals and mixed with some surface water in central Arizona has significantly higher total dissolved solids than groundwater in the Tucson basin, as well as different chemical constituents.
