Water sustainability of large cities in the United States from the perspectives of population increase, anthropogenic activities, and climate change

Balancing water demand and supply with depleting sources and increasing demand needs a multi-dimensional approach given the pace at which the world is urbanizing. This study selected the contiguous United States (CONUS), 42 specific cities and their river basins to determine: Which basins and cities are more susceptible to increased water shortage? Population, water use, hydrologic model and climate model data from CMIP5 were used. Representative Concentration Pathways scenarios: RCP2.6, RCP4.5, RCP6, and RCP8.5 represented different climate change conditions. Period 1 (1950-2004) showed that more areas are affected by monthly runoff and streamflow than annual averages. In some cases, significant decreasing trends in water availability were observed during the summer (June-July-August) and spring (March-April-May) seasons. The second period (2005-2049) indicated an annual increasing trend (more water available) with higher intensity for the RCP6 scenario. Summer and spring showed areas of decreasing trend (less water available) for RCP4.5 and RCP6. Period 3 (2050-2099) exhibited a decreasing trend for the RCP2.6 (Western and Central CONUS, Great Lakes, and FL), RCP4.5 (Southwest CONUS), RCP6 (Western United States), and Central CONUS (RCP8.5). The Mississippi River has a mixed sensitivity to future climate change. The Central Valley of California, Los Angeles, Phoenix, and Tucson can face further challenges as the Colorado River becomes depleted. Seawater desalination and inter-basin water transfer can be considered in future and present policies and structural developments. The West, Southeastern Coast, and FL may consider desalination, while the West and Central CONUS can use the Mississippi for inter-basin transfer.