Putting people and risk in the same picture via hazard ensemble diagrams

Tim LutzDept. of Geology & Astronomy

West Chester UniversityWest Chester, PA

tlutz@wcupa.edu

GSA’s position statement on Natural Hazards (2008):“Geoscientists have a professional responsibility to inform the public about natural hazards and the need to build an increasingly natural hazard-resilient society, thereby enabling more responsible actions and decisions.”

National Research Council’s report on flood risk reduction (2000):“Identifying sound, credible, and effective risk reduction priorities and solutions depends greatly on a well-informed public. The public should be knowledgeable about risk issues and should be given opportunities to express opinions and become involved in risk assessment and risk management activities.”

Tarbuck & Lutgens, 2011

National Flood Insurance Program (NFIP)

Flood Insurance Rate Map (FIRM)

Mean = median = mode = 100 years

Default concept:Probability decreases symmetrically around the mean

Mean = 100 years

Median = 69 years

Mode = 0 years Recurrence interval distribution predicted for independent random events (exponential distribution)

Standard deviation = Mean(e.g., 100 years ± 100 years)

Series 1

Series 2

Series 3

Series 4

Series 5

Five series of random events; average recurrence = 100 years

Series 1

Series 2

Series 3

Series 4

Series 5

Five series of random events; average recurrence = 100 years

Example: USGS 05331000 Mississippi River @ St Paul, MN (114 years of record)

Twin Cities 7 Metro map.png by Davumaya (2008), provided by Wikimedia

The inverse of a magnitude-exceedance probability model can be used to simulate annual peak flows

An ensemble is a set of simulations which together define the distribution of most probable outcomes conditional on exposure.

Unwarranted pessimism

Unwarranted optimism

Weighing of risks

Top of right bank levee in S. St. Paul (29 ft)

Flood walls deployed at St. Paul airport (17 ft)Flood stage (14 ft)

Annual peak flow history Magnitude-frequency model

Magnitude-frequency model Flow ensemble

Flow ensemble

+Rating model =

Stage ensemble

Generalization

History of hazard Magnitude-frequency model Ensemble diagrams

Straightforward extensions

•Seismic hazard Gutenberg-Richter model Ensemble diagrams

•Volcanic hazard VEI1-based m-f model Ensemble diagrams

•Nuclear hazards INES2-based m-f model Ensemble diagrams

1 VEI = Volcano Explosivity Index2 INES = International Nuclear & Radiological Event Scale

For more information about hazard ensemble diagrams, check out Lutz, 2011, JGE v. 59, pp. 5-12; and email me (tlutz@wcupa.edu) for an Excel file that can generate ensembles from annual peak flow data.