Water on an urban planet: Urbanization and the reach of urban water infrastructure

TLDR

Urban growth is increasing freshwater demand, yet the water sources of the world's large cities have never been globally assessed, hindering efforts to evaluate urban water stress distribution and causes. The authors conducted the first global survey of large cities' water sources to assess their distribution and impact on urban water stress. The survey revealed that previous global hydrologic models that ignored urban water infrastructure significantly overestimated urban water stress. Large cities obtain roughly 78 % of their water from surface sources, moving 504 billion liters per day over an average of 27,000 km, yet one in four cities—contributing $4.8 trillion in economic activity—remain water‑stressed, highlighting the importance of strategic source management.

Abstract

Urban growth is increasing the demand for freshwater resources, yet surprisingly the water sources of the world's large cities have never been globally assessed, hampering efforts to assess the distribution and causes of urban water stress. We conducted the first global survey of the large cities' water sources, and show that previous global hydrologic models that ignored urban water infrastructure significantly overestimated urban water stress. Large cities obtain 78 ± 3% of their water from surface sources, some of which are far away: cumulatively, large cities moved 504 billion liters a day (184 km3 yr−1) a distance of 27,000 ± 3800 km, and the upstream contributing area of urban water sources is 41% of the global land surface. Despite this infrastructure, one in four cities, containing $4.8 ± 0.7 trillion in economic activity, remain water stressed due to geographical and financial limitations. The strategic management of these cities' water sources is therefore important for the future of the global economy.