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Water and its major challenges for the 21st century: Effect on arid zones Volume 21, issue 1, janvier-février-mars 2010

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Académie des sciences 23, quai de Conti75006 ParisFrance

What are the great challenges for water resources in the 21st century? There are, of course, a great many but in this article, the emphasis is first on the potential hydrological effects of climate changes: increasing aridity at Mediterranean latitudes with a decrease of arable land and more abundant rainfall elsewhere as well as a probable spatial extension of arable land in northern regions as the permafrost thaws. The main question then discussed concerns the capability of the planet to feed its population in 2050, when the world will reach 9 billion inhabitants, under these changing conditions. The answer is affirmative but it seems probable that entire tracts of the Earth (e.g. all of Asia, the Middle-East and North-Africa) will no longer be self-sufficient in food production and thus obliged to import food, resorting to so-called virtual water. South-America, the OECD countries and the former USSR will be able to produce the food needed in zones with food deficits. The arid zone will naturally experience a very large deficit (reaching 60% of its needs) but it will not necessarily be the most deprived one owing to its economic development, which will generate enough wealth to allow it to import the food it needs. SubSaharan Africa may theoretically be able to produce the food it needs but its slower rate of development threatens to make it equally dependent on virtual water but facing greater difficulties for its importation. Problems of biodiversity conservation and risks of worldwide droughts that may cause famines due to low food stocks are also touched upon.