| Summary: | Water scarcity adversely affects ecosystems, human well-being and the economy. It can be described by water scarcity indices (WSIs) which we calculated globally for the decades 1981–1990 and 2001–2010. Based on a model ensemble, we calculated the WSI for both decades including uncertainties. While there is a slight tendency of increased water scarcity in 2001–2010, the likelihood of the increase is rather low (53%). Climate change played only a minor role, but increased water consumption is more decisive. In the last decade, a large share of the global population already lived under highly water scarce conditions with a global average monthly WSI of 0.51 (on a scale from 0 to 1). Considering that globally there are enough water resources to satisfy all our needs, this highlights the need for regional optimization of water consumption. In addition, crop choices within a food group can help reduce humanity’s water scarcity footprint without reducing its nutritional value.
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