Over half of the world's population lives in cities and urban growth is accelerating. Water-limited arid and semiarid cities are experiencing disproportionate increases in population and land transformation worldwide, increasing stress on water resources and altering natural hydrological systems. Cities face significant challenges in providing clean water for municipal and industrial uses and in managing the environmental water quality and flooding risks that accompany urbanization. The growth of cities will require a continuing investment in infrastructure and in new strategies to adapt to water resource limitations. In the face of demographic and global change, the sustainability of water resources in arid and semiarid cities will be a key challenge. Addressing this challenge will require improved understanding of how water availability and distribution changes with urbanization, and how these changes affect ecosystem service provision and policy responses. Policy and governance decisions aimed at enhancing ecosystem services related to water resources need to be based on scientific evidence to be effective. However, better science does not necessarily lead to better governance; there remains a gap between scientific knowledge and the actions taken as a result of this knowledge. The objective of this project is to improve understanding of the linkages between ecosystem services and governance of water resources. This project will study the natural and human components of semi-arid cities in the US Southwest in order to determine if various attributes of these urbanized systems encourage learning and action that lead to more sustainable outcomes. This research will draw on theoretical frameworks that explicitly link ecological structure and function to ecosystem services to information flows to decision making. Specifically, four key questions will be addressed: (a) How does the frequency, intensity and redistribution of rainfall and runoff influence the eco-hydrologic response of arid and semi-arid urbanized systems and result in emergent ecosystem services? (b) How do human system conditions affect city-level learning about actions that influence ecosystem service provision? (c) How do natural system conditions influence social networks, understanding, and decision-making about water management and infrastructure? And (d) What actions have been taken, in terms of alterations to the built environment, that influence the effect of the built environment on natural system processes? These questions will be answered through a set of field, survey, lab, workshop, and synthetic experiments. Specifically a suite of research sites will be established in Tucson, Sierra Vista, and Yuma, Arizona that will allow investigations from the 1 ha/individual to the 100,000 ha/regional scales. Natural system investigations will focus on how eco-hydrologic processes integrate from the point to large catchment scale and characterize ecosystem services. The social dimensions of this project will focus on the policy and governance sectors to understand learning, decision-making and action at the municipal scale and importantly across social and bioclimatic regions. This work will integrate across natural and human systems by examining how scientific information about ecosystem services develops into decision making and by investigating how policy interventions impact ecosystem services.