City boundaries for global urban water scarcity assessment

Rapid and continuous urbanization has increased water demand in cities worldwide. Global assessments of urban water scarcity should be conducted using gridded hydrological information, but are hampered by the lack of water-resource-based city boundary information. This study introduces HydroUrbanMap (HUM), a global gridded dataset of city boundaries for 1,604 cities at 5 arcmin resolution, incorporating hydrological attributes. HUM consists of two key components: delineation of city boundaries that include the population served by urban water services (supply and drainage), and estimation of accessible surface water sources within and outside these boundaries. The estimated city populations closely match census-based populations, with a correlation coefficient of 0.997. HUM incorporates hydrological inlets and outlets of main rivers in each city by overlaying the city boundaries with the river network. Combining our HUM dataset with outputs from global hydrological models supports city-specific water resource assessments worldwide, filling gaps in cities where data on urban water services are unavailable or incomplete.