Climate variability has always posed important challenges to water resources planners and engineers. Recent hydrologic data from different parts of the world show that the use of traditional stationary series statistical methods to assess risk and uncertainty may not produce reliable estimates. In particular, the 2014–2015 drought in Metropolitan São Paulo that was followed by major flooding in 2016 shows the intensification of climatic extremes in this part of Brazil. The probability of this drought event is only 0.004 when estimated with data available from 83 years of record, until 2013. Was the drought of 2014–2015 a statistical outlier or should one consider it as an event that can occur again along the planning horizon? The paper describes the hydrologic conditions that resulted in the most severe drought ever recorded and the structural and non-structural initiatives taken by water authorities to avoid social chaos in the Metropolitan Region of São Paulo (21 million inhabitants). Furthermore, it discusses how the drought affected the existing water resources development plan, especially the anticipation of investments in water security. Because financial resources are limited, other investments, equally important but less urgent, are being delayed.

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