Hydro-social metabolism: Scaling of birth rates with regional water use.

Population growth is often intuitively linked with proportionally higher use offresh water resources. However, this implies that water use per capita does not change withpopulation growth. We not only find that birth rates of regions are negatively related with itswater use per capita (i.e., higher birth rate is associated with lower water use), but also thatbirth rates scale with the latter with a negative power. We use population and water withdrawaldata from 1950 to 2005 at irregular 5-year intervals; with virtual water content, virtualwater trade and agricultural production data from 1960 to 2000 for the seven continents toinvestigate the scaling relationship and interpret it through the lens of metabolism theory.Our analysis reveals that the scaling exponent lies between −1/3 and −1/2. Deviations fromthe power relationship are observed for Europe and Africa, which are attributed to lower thanexpected and higher than expected birth rates, respectively. Europe's deviation from theaverage scaling relationship may be due to the higher rate of return on human capital inindustrialized countries. But why Africa deviates, while other developing and developedregions follow the power relationship more closely, remains a puzzle. [ABSTRACT FROM AUTHOR]