Estimating urban water demand under conditions of rapid growth: the case of Shanghai

Many of the world's major cities are expected to face significant water shortages in coming decades, largely due to increased demand arising from economic and population growth. In this paper, we estimate the effects of economic and population growth on future public water needs in Shanghai, one of the world's megacities. Despite significant investment in a new reservoir and associated supply systems, and its location at the estuary of one the world's major rivers (the Yangtze), it is widely believed that Shanghai is vulnerable to water shortages, though the causes of this have hitherto not been systematically examined. Our method of estimating future water needs involves extrapolation from past trends and principal component analysis regression, and from the experience of comparable cities around the world, to construct three scenarios of future GDP and population growth and associated water needs. Our analysis shows that under various scenarios, by 2050 the difference between demand and present supply capacity will range between 1.6 and 6 million m(3)/day and that the critical constraint to meeting future demand is treatment capacity, which will need to increase by between 35 and 83% beyond present levels. We discuss four options for managing the estimated deficit between future water demand and supply in Shanghai.