Human–Water Interactions in Urban Systems: Challenges and Opportunities in the Twenty-First Century (Centennial)

Humans have long had profound impacts on hydrologic processes, particularly within cities where complex management structures and land use change create a local hydrologic cycle that is highly altered and hard to predict. Urbanization has significant impacts on the physical environment and the organisms, including humans, living in this system. Urban development results in surfaces that are covered with a variety of materials with distinct thermal, radiative, and moisture properties influencing local and regional energy and water budgets. The conversion from pervious to impervious surfaces changes hydrologic response by increasing flood risk and degrading water quality. Moreover, contrasting aerodynamic properties of buildings significantly change surface roughness and turbulence. The effects associated with modified urban landscapes also extend to degraded air quality, increases in local temperatures, changes in regional atmospheric circulation and alterations in precipitation patterns. Urban populations also increase regional water demand and water supply gaps are common throughout the western U.S. Due to the continuing transition from rural to urban living, most humans now live in cities. This trend is expected to continue, and by 2030 it is estimated that over two-thirds of the world’s population will reside within urban areas. The combination of a rapidly densifying urban population with climate change creates significant challenges for cities in their quest to better manage this human-physical relationship. As growth intensifies and cities redesign the urban framework, opportunities arise for rethinking our relationship with cities. This presentation will overview recent advances in predicting land-atmosphere-water interactions in urban areas, including better understanding water consumption patterns and drivers, improving tools for optimizing stormwater capture, evaluating the co-benefits of green infrastructure and modeling energy-water budgets in cities. More accurate representation of land-atmosphere-water processes in urban systems is critical for regional resource management, especially in water stressed semi-arid cities of the world.