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Oki&Kanae Lab.

PI: Masashi Kiguchi
Institution: University of Tokyo
Abstract:
Together with changes in water withdrawal, changes in the availability of water resources due to global climate warming could also influence1 the world water resources stress situation. Here, we investigate how world water resources stress will likely change under scenarios presented by the Special Report on Emission Scenarios (SRES) with integrating the water withdrawal projections presented in the first part of this study. First, potential changes in water availability are investigated using a multi-model analysis of the ensemble outputs of six general circulation models (GCMs) from worldwide organisations. The analysis suggests that although climate warming might create greater availability of water resources, the amplitude of water resource change varies widely in some regions depending on the GCM used. The change predicted by the models was consistent for boreal regions of northern Canada and Siberia and tropical areas near the Equator. In most of Europe, the eastern U.S., and parts of South America, the six GCMs suggest significant to subtle changes in runoff. However, a significant decreasing trend in runoff due to climate warming is forecast for southern Europe. For other regions, the model results show large uncertainty in change amplitudes and even directions. Second, we investigated water-stressed basins, the number of people living in highly water-stressed basins, and changes in these categories using two indices (W/Q and Q/c) at the basin scale. Indices Q/c and W/Q indicate that approximately 1.75 billion and 2.53 billion people, respectively, currently live in highly water-stressed basins. These numbers will increase in the future and possibly double by the 2050s according to SRES scenarios A1b, A2, and B1. Finally, we examined the relative impacts of population growth, water use change, and climate warming on world water resources using the world highly water-stressed population as an overall indicator. The results suggest that population growth and socioeconomic development are the major causes of increasing stress on world water resources. Climate warming could mitigate world water stress to a limited extent. However, even though climate warming may create greater water availability, many basins worldwide will likely continue to experience water stress. Therefore, water use efficiency must be improved globally to reduce the net water withdrawal. A comparison of the world water-stressed population amongst different projections was also conducted in this paper.
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