Estimating Hurricane Risk and Damages in Current and Future Climates

Estimating Hurricane Risk and Damages in Current and Future

Climate

Estimating Hurricane Risk and Damages in Current and Future

Climate

Kerry EmanuelLorenz Center, MIT

Program

Brief overview of hurricanes

What have hurricanes been like in the past, and how will they be affected by global warming?

How should we assess hurricane risk?

Brief Overview of Tropical Cyclones

The View from Space

Igor, 2010

Annual Cycle of Tropical Cyclones

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec NH Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun SH

a

a

Northern Hemisphere

(NH)

Southern Hemisphere

(SH)Nu

mb

er

of

Ev

en

ts p

er

Mo

nth

Hurricane Risks:

Wind

Storm Surge

Rain

Basic Hurricane Economics

Windstorms Account for Bulk of Insured Losses Worldwide

Total US Damages by Natural Hazard, 1980-2012

Source: NOAA

Source: Roger Pielke, Jr.

Total U.S. Hurricane Damage by Decade, in 1010 2004 U.S. Dollars

Population of Florida, 1790-2004

Source: Roger Pielke, Jr.

Total Adjusted Damage by Decade, in 1010 2004 U.S. Dollars

U.S. Hurricane Damage, 1900-2004,Adjusted for Inflation, Wealth, and Population

Total Number of Landfall Events, by Category, 1870-2004

Limitations of a strictly statistical approach to hurricane risk assessment

>50% of all normalized U.S. hurricane damage caused by top 8 events, all category 3, 4 and 5>90% of all damage caused by storms of category 3 and greaterCategory 3,4 and 5 events are only 13% of total landfalling events; only 30 since 1870 Landfalling storm statistics are inadequate for assessing hurricane risk

Overcoming Limits of a History-Based Statistical Approach

barrier beach

backbarrier marshlagoon

barrier beach

backbarrier marshlagoon

a)

b)

Source: Jeff Donnelly, WHOI

upland

upland

flood tidal delta

terminal lobes

overwash fan

overwash fan

Method 1: Paleotempestology

Method 2: Risk Assessment by Direct Numerical Simulation of Hurricanes:

The Problem

The hurricane eyewall is a front, attaining scales of ~ 1 km or less

At the same time, the storm’s circulation extends to ~1000 km and is embedded in much larger scale flows

The computational nodes of global models are typically spaced 100 km apart

Histograms of Tropical Cyclone Intensity as

Simulated by a Global Model with 50 km grid

point spacing. (Courtesy Isaac Held, GFDL)

Category 3

Global models do not simulate the storms that

cause destruction

ObservedModeled

Numerical convergence in an axisymmetric, nonhydrostatic model (Rotunno and Emanuel, 1987)

How to deal with this?

Option 1: Brute force and obstinacy

How to deal with this?Option 1: Brute force and obstinacy

Option 2: Applied math and modest resources

Time-dependent, axisymmetric model phrased in R space

Hydrostatic and gradient balance above PBL

Moist adiabatic lapse rates on M surfaces above PBL

Boundary layer quasi-equilibrium convection

Deformation-based radial diffusion

Coupled to simple 1-D ocean model

Environmental wind shear effects parameterized

21

2M rV fr 21

2fR M 2 sinf

How Can We Use This Model to Help Assess Hurricane Risk in Current and Future Climates?

Risk Assessment Approach:

Step 1: Seed each ocean basin with a very large number of weak, randomly located cyclones

Step 2: Cyclones are assumed to move with the large scale atmospheric flow in which they are embedded, plus a correction for the earth’s rotation and sphericity

Step 3: Run the CHIPS model for each cyclone, and note how many achieve at least tropical storm strength

Step 4: Using the small fraction of surviving events, determine storm statistics

Details: Emanuel et al., Bull. Amer. Meteor. Soc, 2008

Comparison of Random Seeding Genesis Locations with Observations

Cumulative Distribution of Storm Lifetime Peak Wind Speed, with Sample of 1755 Synthetic Tracks

90% confidence bounds

Return Periods

Sample Storm Wind Swath

Accumulated Rainfall (mm)

Storm Surge Simulation

SLOSH mesh~ 103 m

ADCIRC mesh~ 102 m

Battery

ADCIRC model(Luettich et al. 1992)

SLOSH model(Jelesnianski et al. 1992)

ADCIRC mesh~ 10 m

(Colle et al. 2008)

Taking Climate Change Into Account

Captures effects of regional climate phenomena (e.g. ENSO, AMM)

Modeling Center Institute ID Model Name Average Horizontal Resolution

National Center for Atmospheric Research

NCAR CCSM4 1.25o X 0.94o

NOAA Geophysical Fluid Dynamics Laboratory

GFDL CM3 2.5 o X 2.0 o

Met Office Hadley Center MOHC HADGEM2-ES 1.875 o X 1.25 o

Max Planck Institute for Meteorology

MPI MPI-ESM-MR 1.875 o X 1.865 o

Atmosphere and Ocean Research Institute (The

University of Tokyo), National Institute for

Environmental Studies, and Japan Agency for

Marine-Earth Science and Technology

MIROC MIROC5 1.41 o X 1.40 o

Meteorological Research Institute

MRI MRI-CGCM3 2.81 o X 2.79 o

CMIP5 Models

Return Periods based on GFDL Model

Return Periods of Storm Total Rainfall at New HavenGFDL Model

GCM flood height return level, Battery, Manhattan

(assuming SLR of 1 m for the future climate )

Black: Current climate (1981-2000)Blue: A1B future climate (2081-2100)Red: A1B future climate (2081-2100) with R0 increased by 10% and Rm increased by 21%

Lin et al. (2012)

Human Adaptation: Century Time Scales

Current and Future Probability Density of U.S. Damages, MIROC

Model

Current and Future Damage Probability, MIROC Model

A Black Swan: Dubai

Aerts, C. J. H. J., W. J. W. Botzen, K. Emanuel, N. Lin, H. de Moel, and E. O. Michel-Kerjan, 2014: Evaluating flood resilience strategies for coastal megacities. Science, 344, 473-475.

Benefit-Cost Ratios

From: American Climate Prospectus Economic Risks in the United States

Sea level rise alone

Sea level rise + changing storms

Summary

History is too short and imperfect to estimate hurricane risk

Better estimates can be made from paleotempestology and downscaling hurricane activity from climatological or global model output

Hurricanes clearly vary with climate and there is a risk that hurricane threats will increase over this century

Spares

What is a Hurricane?

Formal definition: A tropical cyclone with 1-min average winds at 10 m altitude in excess of 32 m/s (64 knots or 74 MPH) occurring over the North Atlantic or eastern North Pacific

A tropical cyclone is a rapidly rotating storm system between 100 and 1000 km in diameter and characterized by low surface pressure, strong winds, and a spiral arrangement of thunderstorms. The rotational character of the storm is a consequence of conservation of angular momentum imparted by the Earth’s rotation as air flows inward toward the rotation axis.

What is a Tropical Cyclone?

The word Hurricane is derived from the Mayan word Huracan and the Taino and Carib word

Hunraken, a terrible God of Evil, and brought to the West by Spanish explorers

Blow, winds, and crack your cheeks! rage! blow! You cataracts and hurricanoes, spout Till you have drench’d our steeples, drown’d the cocks!

-- King Lear

ADCIRC Mesh

Heat Engine Theory Predicts Maximum Hurricane Winds

MPH

Black Swans

Peak Surge at each point

along Florida west coast