Systems for management of water throughout the developed world have been designed and operated under the assumption of stationarity. Stationarity--the idea that natural systems fluctuate within an unchanging envelope of variability--is a foundational concept that permeates training and practice in water-resource engineering. It implies that any variable has a time-invariant probability density function, whose properties can be estimated from the instrument record. In view of the magnitude and ubiquity of the hydroclimatic change apparently now under way, however, we assert that stationarity is dead and should no longer serve as a central, default assumption in water-resource risk assessment and planning. Finding a suitable successor is crucial for human adaptation to changing climate.