Photo courtesy of NASA: STS047-151-618 Hurricane Bonnie (1992)

Does Tropical Cyclone Modification Make Sense? A Decision-Analytic Perspective

Kelly Klima

CEDM Annual MeetingMay 21-22, 2012

Photo courtesy of NASA: STS047-151-618 Hurricane Bonnie (1992)

Two general approaches exist for controlling hurricane damage

Hardening structuresCurrently practiced nationwide

Called “mitigation” by FEMA and others

Includes shutters, dams, better roof connections, etc

Works better for moderate storms

3Does tropical cyclone modification make sense?

Hurricane modificationTheorized since 1930s

DHS has recently reopened research into the topic

Works better for large storms

Today we will discuss three specific questions relating to whether tropical cyclone modification makes sense• What wind and storm surge damage reductions

are possible for different adaptation and modification techniques?

• When might it be desirable to steer a hurricane?

• If hurricane modification were feasible, would public perceptions prevent implementation? 4

See Poster Session!

Today we will discuss three specific questions relating to whether tropical cyclone modification makes sense• What wind and storm surge damage reductions

are possible for different adaptation and modification techniques?

• When might it be desirable to steer a hurricane?

• If hurricane modification were feasible, would public perceptions prevent implementation? 5

I examined a probabilistic hurricane making landfall on the east coast of Florida

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Assumptions:Nonzero modification cost

Instantaneous implementation

Steering away from track with highest damages

No correlation between outcomes

When steering a hurricane away from the track with highest damages, the policy choice depends on assumptions

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• Focus: Total damages. Steering: Works perfectly.– If modification cost << weighted damages: YES– If modification cost >> weighted damages: NO

• Focus: Mostly wind or storm surge damage. Steering: Works perfectly.– If damages increase but wind (or storm surge) damages

decrease: MAYBE

• Focus: Either scenario above. Steering: Uncertain.Damages: Increase is much worse than decrease. – If increase = 2x decrease: YES when >65% of modifications

result in a “good” outcome (Klima 2011 values)

Using benefit-cost analysis, the best method to reduce damages varies

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• Regions experience more surge damages for short return periods, and more wind damages for long periods

• Storm surge net costs are best reduced through a surge barrier

• Wind net costs are best reduced by a portfolio of techniques including tropical cyclone modification

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Photos courtesy of Kithil, FEMA,Hurricane Proof,Matthews House Movers

Today we will discuss three specific questions relating to whether tropical cyclone modification makes sense• What wind and storm surge damage reductions

are possible for different adaptation and modification techniques?

• When might it be desirable to steer a hurricane?

• If hurricane modification were feasible, would public perceptions prevent implementation? 9

CMU’s mental models methodology identifies people’s beliefs to inform the design of risk communication materials• Format

– Small set of interviews– Questions are refined– Large set of surveys

• Previously used to examine

10Carbon Capture

and Storage

I use the mental models approach to examine how Florida residents perceive hurricane modificationInterview (10 participants)5 women

7 live in a house

10 have been in a hurricane

11There were four main findings.

Survey (157 participants)66.7% women

57.3% live in a single story home

92% have been in a hurricane

Age: 40 (SD=15)

Salary: $74.3K (SD=$52.9K)

The four findings characterize Florida residents’ mental models and could be used to inform communication.

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• No one recognized or trusted hurricane modification

• Modification was expected to lead to changes in path, not strength

• Anger was weaker when damages were lower than predicted or when path was unaltered

• Participants recognizing uncertainty reported more anger at scientists across modification scenarios

Conclusion• Using benefit-cost analysis, the best method to reduce

damages varies– Wind = Portfolio of techniques including modification– Storm surge = Dikes

• Risk communication should be designed to complement residents’ mental models – Residents question effectiveness and expect modification to

focus more on changing paths than on changing intensity – People are angrier about changing paths than about

changing intensity, especially when they recognize forecast uncertainty

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Clearly it is premature to call for the development of tropical cyclone modification

• Benefit-cost analysis alone does not capture the complexity of this decision

• Other issues include uncertainty of deployment, liability/ethics, risk tolerance, political/budgetary/time restraints, multiple decision makers

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Kelly Klima, Ph.D.Post-doctoral Fellow

Engineering and Public Policy, Carnegie Mellon Universitykklima@andrew.cmu.edu

K. Klima, M. G. Morgan, I. Grossmann, K. Emanuel. Does it Make Sense to Modify Tropical Cyclones? A Decision Analytic Assessment. Environmental Science & Technology. 2011. 45:10 pp 4242–4248.

K. Klima, W. Bruine de Bruin, M. G. Morgan, I. Grossmann. Public Perceptions of Hurricane Modification. Risk Analysis. 2011.

K. Klima, N., Lin, K. Emanuel, M. G. Morgan, I. Grossmann,. Hurricane Modification and Adaptation in Miami-Dade County, Florida. Environmental Science & Technology, 2012, 45 (2), pp. 636-642.

Funding provided by:

Extended Public Perceptions

Finding 1: Interviewees neither recognized nor trusted hurricane modification

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• Only one person suggested hurricane modification as a way to decrease damages from hurricanes

• “Have you ever heard about the possibility of changing hurricanes to reduce their damage?”

“You can’t change nature”

“It will never be possible”

Hurricanes are “too big and powerful to

be changed”

The government might be “using

some kind of secret weapon or something”

Finding 1: Survey participants agreed with interviewee statements

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(R) refers to statements that were reverse-coded to denote agreement with the ineffectiveness of hurricane modification. One-sample t-tests examined whether mean

agreement with statements differed from the midpoint (=3), indicating beliefs held with stronger conviction (*** p<.001; ** p<.01).

StatementM (SD) Agreement

Today, it is possible to change a hurricane to reduce its damage (R)

4.68 ***

(1.29)It is a bad idea to change a hurricane because it might make things worse

3.59 ***

(1.80)Hurricanes are too big and powerful to ever be changed by humans

3.49 **

(1.83)At some point in the future, it will be possible to change a hurricane to reduce its damage (R)

3.15 (1.66)

We will never develop the technology to change a hurricane

2.76(1.77)

Finding 1: Hurricane modification was perceived as a less effective strategy for damage reduction than hardening

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Techniques perceived as effective include:

Courtesy of 123RF, Hunter Tree Removal, FEMA, Hurricane Proof, Home Depot, Matthews House Movers, DeclutterHome

Finding 2: Hurricane modification was expected to lead to changes path, but not necessarily strength

Type of hurricane

Initiallyprojectedintensity

Percent expecting change from initially projected landfall location

Percent expecting reduction from initially projectedcategory

Unmodified Category 5 4.3% 25.9%

Modified Category 5 16.4%*** 40.5%**

Unmodified Category 1 6.0% 6.4%

Modified Category 1 16.4%* 0.9%*

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T-tests were used to test whether hurricane modification significantly affected the number of selected outcomes (*** p<.001; * p<.05)

Finding 3: Reported anger was weaker when damages were lower than predicted or when path was unaltered

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Hurricane scenarioPathcompared to prediction

Damage compared to prediction

Mean (SD) anger at scientists, 0 (=Not at all) to 6 (=Extremely)

Same More 2.89 (2.10)Same Same 1.75 (1.86)***Same Less 1.03 (1.52)***Different More 3.48 (2.08)**Different Same 3.06 (2.10)Different Less 1.88 (1.80)***One-sample t-tests examined whether mean anger differed from the midpoint (=3),

indicating relative strength of the reported emotion (*** p<.001; ** p<.01).

Finding 4: Participants said nature can’t be perfectly predicted…..

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… but those recognizing uncertainty inherent in hurricane prediction reported more anger at scientists across modification scenarios

Courtesy of NASA

Multivariate Analysis of Variance (MANOVA)

Used when there is more than one dependent variable, such as ratings of effectiveness for multiple damage reduction strategies. It examines the effect of one or more independent variables on the means of the dependent variables, as well as interaction effects between the levels of the independent and the dependent variables. Like univariate Analysis of Variance (ANOVA) t, it uses the F-test to examine these effects.

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Cronbach’s alpha

Mathematically equivalent to the average value of all possible split-half correlations. Indeed, a split-half correlation is the correlation between mean two mean ratings computed from two halves of the same set of items. Hence, it is an indicator of internal consistency reliability across items.

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McNemar change tests

Designed for use with 2 x 2 contingency tables of nominal data obtained in a repeated-measures design, for example to compare whether expected change (yes vs. no) is more likely with different types of hurricanes (modified vs. unmodified).

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