A global water scarcity assessment under Shared Socio-economic Pathways – Part 2: Water availability and scarcity

摘要

A global water scarcity assessment for the 21st century was conducted underthe latest socio-economic scenario for global change studies, namely SharedSocio-economic Pathways (SSPs). SSPs depict five global situations withsubstantially different socio-economic conditions. In the accompanying paper,a water use scenario compatible with the SSPs was developed. This scenarioconsiders not only quantitative socio-economic factors such as population andelectricity production but also qualitative ones such as the degree oftechnological change and overall environmental consciousness. In this paper,water availability and water scarcity were assessed using a globalhydrological model called H08. H08 simulates both the natural water cycle andmajor human activities such as water abstraction and reservoir operation. Itsimulates water availability and use at daily time intervals at a spatialresolution of 0.5° × 0.5°. A series of globalhydrological simulations were conducted under the SSPs, taking into accountdifferent climate policy options and the results of climate models. Waterscarcity was assessed using an index termed the Cumulative Abstraction toDemand ratio, which is expressed as the accumulation of daily waterabstraction from a river divided by the daily consumption-based potentialwater demand. This index can be used to express whether renewable waterresources are available from rivers when required. The results suggested thatby 2071–2100 the population living under severely water-stressed conditionsfor SSP1-5 will reach 2588–2793 × 106 (39–42% of totalpopulation), 3966–4298 × 106 (46–50%),5334–5643 × 106 (52–55%), 3427–3786 × 106(40–45%), 3164–3379 × 106 (46–49%)respectively, if climate policies are notadopted. Even in SSP1 (the scenario with least change in water use andclimate) global water scarcity increases considerably, as compared to thepresent-day. This is mainly due to the growth in population and economicactivity in developing countries, and partly due to hydrological changesinduced by global warming.