The Demise of StationarityFormulating an Engineering Response to the Effects of Global Climate Change for Design of Hydraulic Structures

Dr. Eric Loucks, P.E. October 29, 2008

Science Vol 319, p. 573, 1 February 2008

What does Stationarity mean?

Stationarity is a consistency of a time series over times. At a minimum, fixed Mean and Variance.

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Why is it important?

Flood frequency/ flood risk is usually expressed by:

Qn = mq + Kn sq

Qn = n-year flood quantilemq = mean annual floodsq = standard deviation

K = factor based on distribution

Procedure assumes Stationarity.

Flood Estimates: How Good Are they? Ray K. Linsley, Water Resources Research 22:9, August 1986

Milwaukee River at Milwaukee Historical Annual Floods 1915-2007

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Milwaukee River at Milwaukee Historical Annual Floods 1915-2007

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Mean = 5190 cfs Mean = 5220 cfs

DuPage River at Shorewood Historical Annual Floods 1941-2008

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DuPage River at Shorewood Historical Annual Floods 1941-2008

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Mean = 4160 cfs

Cv = 0.616

Mean = 4550 cfs

Cv = 0.617

Menomonee River at Milwaukee Historical Annual Floods 1962-2007

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Menomonee River at Milwaukee Historical Annual Floods 1962-2007

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Menomonee River at Milwaukee Historical Annual Floods 1962-2007

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Mean = 3950 cfs Mean = 4870 cfs

Buffalo Bayou Historical Annual Floods 1937-2007

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Sea Level at Galveston 1909-2005

Mean Annual Sea Level at Galveston Texas

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P. J. Webster et al., Science 309, 1844 -1846 (2005)

Sea-surface Temperature Trends

Global/Regional Climate Models

Published by AAAS

R. P. Allan et al., Science 321, 1481 -1484 (2008)

Published by AAAS

R. P. Allan et al., Science 321, 1481 -1484 (2008)

Chicago Illinois, Sept. 13, 2008

8 to 10 inches of Rainfall

Baraboo River at Baraboo Wisconsin

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Baraboo River at Baraboo Wisconsin

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Baraboo River June 8, 2008 - 19,000 cfs

Baraboo River June 8, 2008 - 19,000 cfs

Marble Falls – June 28, 2007

16 inches of rain in 6 hours

Hurricane Charley Track- 1986

Stationarity is not dead, but it’s in deep, deep trouble.

• The profession(s) are not prepared to manage design risk in the face of changing hydrology.

- Changes are not understood

- No uniform/accepted techniques for frequency analysis

- GCM’s aren’t ready to replace historical records

• Immediate need to revise the practice of risk-based design in Water Resources Engineering