It is well established that hydrological and ecological processes are closely coupled in natural ecosystems. The nature of this coupling is greatly altered in urban environments, where the built environment has modified ecosystem structure and function. These alterations are particularly pronounced in arid urban environments where the hydrological response is typically very flashy. We present a conceptual model of ecohydrological interactions in arid urban environments, focusing on feedbacks among hydrology, ecosystem structure, biogeochemistry, and erosion across multiple spatial scales. We present a case study from the Phoenix metropolis, where significant changes in land use and stream channel structure have occurred during the process of urbanization. These changes include the channelization, engineering, and damming of natural channels. Using stream flow data from a series of gauges distributed within the Phoenix metropolis, we investigate how within-channel hydrology varies across watersheds of different sizes, land use type, and channel structure. We then hypothesize the effects that these observed changes in hydrologic function have on riparian ecosystems, in-channel biogeochemical cycling, and erosion processes.