Climate and land use change (hereafter referred to simply as “climate change”) will further increase the number of urban dwellers facing water shortage (Fig. 1). In some cities, water availability will decrease owing to climate change, whereas other cities will see increases, with more cities having less water than having increased flows. Averaging across all climate change scenarios, ≈100 million more urbanites will live under perennial shortage under climate change conditions than under current climate. At the 100-km buffer difference, the equivalent figure is 22 million. Climate change does not greatly change the aggregate number of urban residents facing seasonal shortage, although the effect for particular cities may be large. Our hydrologic model does not fully account for water storage through glaciers and snowpack, an important source of water for many cities (17–19), and aggregate effects might emerge if this issue could be investigated in greater depth. Interestingly, there is relatively little variation among the impacts on water shortage of our four scenarios of climate change. At the 100-km buffer distance, the coefficient of variation of perennial and seasonal water shortage across all four climate change scenarios and both demographic scenarios was only 2.7% and 0.3%, respectively.
Fig. 2 shows water shortage status for cities of more than 1 million people in 2000. Perennial water shortage is generally confined to cities in the Middle East and North Africa. Seasonal shortage is much more geographically widespread, occurring on all continents and in many different climates. Rapidly urbanizing China and India will have a large number of cities with seasonal water shortage by 2050.
Climate and land use change (hereafter referred to simply as “climate change”) will further increase the number of urban dwellers facing water shortage (Fig. 1). In some cities, water availability will decrease owing to climate change, whereas other cities will see increases, with more cities having less water than having increased flows. Averaging across all climate change scenarios, ≈100 million more urbanites will live under perennial shortage under climate change conditions than under current climate. At the 100-km buffer difference, the equivalent figure is 22 million. Climate change does not greatly change the aggregate number of urban residents facing seasonal shortage, although the effect for particular cities may be large. Our hydrologic model does not fully account for water storage through glaciers and snowpack, an important source of water for many cities (17–19), and aggregate effects might emerge if this issue could be investigated in greater depth. Interestingly, there is relatively little variation among the impacts on water shortage of our four scenarios of climate change. At the 100-km buffer distance, the coefficient of variation of perennial and seasonal water shortage across all four climate change scenarios and both demographic scenarios was only 2.7% and 0.3%, respectively.Fig. 2 shows water shortage status for cities of more than 1 million people in 2000. Perennial water shortage is generally confined to cities in the Middle East and North Africa. Seasonal shortage is much more geographically widespread, occurring on all continents and in many different climates. Rapidly urbanizing China and India will have a large number of cities with seasonal water shortage by 2050.
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