Distribution Matters: Sensitivity of Gridded Data of Population and Economic Conditions to Global Water Scarcity Assessment
Abstract Availability of water per capita is among the most fundamental water-scarcity indicators and has been used extensively in global grid-based water resources assessments. Recently, it has been extended to include the economic aspect, a proxy of the capability for water management. We applied the extended index globally under SSP–RCP scenarios using gridded population and economic conditions from two independent sources and unexpectedly found that the gridded data were significantly sensitive to global water-scarcity assessment. One projection assumed urban concentration of population and assets, whereas the other assumed dispersion. In analyses using multiple SSP–RCP scenarios representing a world of sustainability (SSP1–RCP2.6), regional rivalry (SSP3–RCP7.0), and fossil fuel development (SSP5–RCP8.5) in the future, multiple GCMs, and two gridded datasets showed that the water-scarce population ranges from 0.32–665 million. Uncertainties in the SSP–RCP and GCM scenarios were 6.58–489 million and 0.68–315 million, respectively. The population distribution assumption had a similar impact, with an uncertainty of 169–338 million. These results highlight the importance of the subregional distribution of socioeconomic factors for predicting the future global environment.