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Increasing Risk of Great Floods in a Changing ClimateChanges in the water cycle are expected to accompany global warming. Scientific assessments of the subject have concluded little, because natural hydrologic variability makes detection of hydrologic change intrinsically difficult. A statistically significant upward trend in the frequency of exceedance of the 100-year discharge on major world rivers was detected by Milly et al. (2002, abstract, paper), who showed the trend to be consistent with retrospective simulations of global warming in a climate model. Furthermore, the same model projects a many-fold increase in such floods during the 21st century. These results are preliminary, based on imperfect, incomplete observations and an imperfect, incomplete model. Our project is working with other scientists to improve our understanding of the historical record and to build models that can more faithfully simulate the workings of the climate system. The prospect of substantial regional changes in streamflow characteristics adds a new dimension to the issue of global warming. Furthermore, with respect to hydrologic practice, this finding indicates that the stationarity assumption (that the past is representative of the future) is becoming increasingly untenable, not only where human habitation and development have changed the land surface or its “plumbing,” but everywhere on Earth.
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U.S. Department of Interior | U.S.
Geological Survey |