National Research Program
Making a central assumption of water management obsolete
Water-resource risk assessment and planning are currently based on the notion that factors such as precipitation and streamflow fluctuate within an unchanging envelope of variability. Anthropogenic changes to Earth's climate are altering the means and extremes of these factors so that this paradigm of stationarity no longer applies, causing a basic principle that guides how infrastructure decisions are made to be in doubt.[Changes in runoff volume projected by the middle of the 21st century relative to 1900-1970 historical conditions. Color, denoting percentage change, represents the median value from 12 climate models.]
Scientists and engineers have long worked under the assumption that nature will behave in the future in the same way it behaved in the past. For example, nature will always bring us surprises in the form of floods and droughts. This principle (called "stationarity") says that the risks of such events at any given location do not change as the years roll by.
However, in a February 2008 article in Science, USGS and other scientists note that the principle of stationarity is "dead" because substantial anthropogenic change of Earth’s climate is altering the means and extremes of precipitation, evapotranspiration, and rates of discharge of rivers. Thus, because of changes in land use and climate, we must modify our approach to solving water resources problems. The world invests over $500 billion per year in water infrastructure. Optimal use of available climate information will require extensive training of (both current and future) hydrologists, engineers, and managers in nonstationarity and uncertainty. The new approach must recognize that the future is likely to be rather different from the past, but must also recognize that we are likely to remain highly uncertain of what the future will bring in any given river basin.
Milly, P.C.D., Betancourt, J., Falkenmark, M., Hirsch, R.M., Kundzewicz, Z.W., Lettenmaier, D.P., and Stouffer, R.J., 2008, Stationarity is dead: Whither water management?: Science, v. 319, no. 5863, p. 573-574.
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For additional information, see the project, Continental Water, Climate and Earth-System Dynamics, or contact Chris Milly, firstname.lastname@example.org