If Stationarity Dies, How Will We Know?

When Milly et al. pronounced the death of stationarity in Science magazine last year, lots of folks in the water world took notice. Stationarity is the idea that the envelope of variability we’ve seen is the envelope of variability we’ll get in the future. Not so in a climatically changing world?

Now come Gabriele Villarini and colleagues with an elaborate set of statistical tests poking at peak flow in 50 rivers and saying, in essence, if stationarity is dead they can’t seem to find a corpse:

Despite the profound changes that have occurred to drainage basins throughout the continental United States and the recognition that elements of the hydrologic cycle are being altered by human-induced climate change, it is easier to proclaim the demise of stationarity of flood peaks than to prove it through analyses of annual flood peak data.

Since I don’t begin to understand the technical details of their analysis, I’ll ask the wonks in the audience: Is stationarity back alive?


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  3. As far as I can tell, stationarity (like Schrodinger’s cat and hurricane average intensities) is neither dead nor alive. On mass balance terms, stationarity (constant mean and variation of flood data) must change, but the data gathered by these authors does not support a change.

    So, the obvious question is “Why not?” Something important appears to be missing from the equation. A possibility is that the change is in the groundwater recharge rate and not in the flood data. My idea here is that flood levels are a rapid event that is insensitive to total rainfall but that aquifer recharge is a slower, rainfall dependent event.

    But I am just guessing.

  4. Is stationarity the new sustainability? I hear a lot of the same people throwing both terms about frequently, but often wonder whether they are all using the same definition.

  5. No, this doesn’t claim stationarity has been born again. There are other variables that do show statistically significant trends. But this study does have implications for flood design. Flood frequency analysis is the basis of flood protection, and it assumes the future will be the same as the past. Villarini’s study suggests that is still a viable approach, at least for the studied sites.

  6. Stationarity was a myth! it never existed except in our wishful thinking. Look at global temperature charts for the Quaternary Epoch… or just look at wavecut terraces 300 feet above valley floors in the Great Basin.

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