Water population density: Global and regional analysis

The exponential growth of population and water use has intensified water stress and scarcity. Understanding the demographic forces is necessary to maintain the delicate balance between humans' need for freshwater and finite water resources. To analyze the population and water nexus simultaneously, the water population density (WPD) indicator is developed, and the past, present, and future changes in water-population interaction at both global and regional scales are investigated. Results revealed that WPD (people per mm 3 ) is a valuable indicator that can be applied on regional and global scales. Also, the integration of land population density (LPD) and WPD represents a synoptic-scale identification of the critical land and water challenges and guides water policies towards efficient management of land and water resources. By adopting tree analysis, this study classified the world’s countries and regions as having low, moderate, high, or extremely high WPD. In light of the findings, the per capita availability of water will significantly decrease in the high and extremely high WPD regions. Better management of population distribution and water resources, as well as increased public awareness about the advantages of efficient water use, can present some opportunities to reduce water stress in the high and extremely high WPD countries and regions. Also, this indicator can be used for planning water resources and adaptation to climate change.