Globally, freshwater shortageis one of the most dangerous risks for society. Changing hydro-climaticand socioeconomic conditions have aggravated water scarcity over the pastdecades. A wide range of studies show that water scarcity will intensify inthe future, as a result of both increased consumptive water use and, in someregions, climate change. Although it is well-known that El Ni?o–SouthernOscillation (ENSO) affects patterns of precipitation and drought at globaland regional scales, little attention has yet been paid to the impacts ofclimate variability on water scarcity conditions, despite its importance foradaptation planning. Therefore, we present the first global-scale sensitivityassessment of water scarcity to ENSO, the most dominant signal of climatevariability.We show that over the time period 1961–2010, both water availability andwater scarcity conditions are significantly correlated with ENSO-drivenclimate variability over a large proportion of the global land area (> 28.1 %);an area inhabited by more than 31.4 % of theglobal population. We also found, however, that climate variability alone isoften not enough to trigger the actual incidence of water scarcity events.The sensitivity of a region to water scarcity events, expressed in terms ofland area or population exposed, is determined by both hydro-climatic andsocioeconomic conditions. Currently, the population actually impacted bywater scarcity events consists of 39.6 % (CTA: consumption-to-availability ratio) and 41.1 % (WCI: water crowding index) of the globalpopulation,whilst only 11.4 % (CTA) and 15.9 % (WCI) of the global population is atthe same time living in areas sensitive to ENSO-driven climate variability.These results are contrasted, however, by differences in growth rates foundunder changing socioeconomic conditions, which are relatively high inregions exposed to water scarcity events.Given the correlations found between ENSO and water availability andscarcity conditions, and the relative developments of water scarcity impactsunder changing socioeconomic conditions, we suggest that there is potentialfor ENSO-based adaptation and risk reduction that could be facilitated bymore research on this emerging topic.
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