Hurricanes - the predictable hazards?
Alistair McNaught - 2001
Overview of lecture
Nov 2000 -
Nov 2001
Predictable?
Unpredictable?
The year so far?
Hurricanes - the predictable hazards?
Alistair McNaught - 2001
Predictable times?
Predictable places?
Predictable impacts?
Hurricanes - the predictable hazards?
Alistair McNaught - 2001
Predictable times?Short term annual patterns
To make a hurricane take
• warm ocean - 27ºC
• upper atmosphere weather
• a dash of Coriolis force - the spinning effect of the Earth’s rotation
N.hemisphere - J F M A M J J A S O N D
S.hemisphere - J F M A M J J A S O N D
Hurricanes - the predictable hazards?
Alistair McNaught - 2001
Predictable times?Medium term patterns
To make a hurricane take
• warm ocean - 27ºC
• upper atmosphere weather
• a dash of Coriolis force
El Niño / La Niña
Antarctic circum-polar wave
Pacific decadal oscillation
Hurricanes - the predictable hazards?
Alistair McNaught - 2001
Predictable impacts?Wind * Waves * Rain * Surge
Saffir Simpson Scale - 1 2 3 4 5
mph 74 96 111 131 156+ (70m/s)
Impacts on:
Buildings:
Loss
as
% v
alu
e
Windspeed (m/s)
20
15
10
5
0
0 20 40 60 80
SS4 SS5
Source - Swiss Re Insurance publication
Agriculture:
Forestry:
Ecosystems:
Infrastructure:
Hurricanes - the predictable hazards?
Alistair McNaught - 2001
Predictable impacts?Wind * Waves * Rain * Surge
Hurricanes - the predictable hazards?
Alistair McNaught - 2001
Predictable impacts?Wind * Waves * Rain * Surge
Eg Sept 99: Hurricane Floyd 14 inches (35cm) rain in 3 hrs. Rivers rising 10 - 15 feet (3 - 4.5 m)
Oct 1998: Hurricane Mitch
25 inches rainfall (63cm) in 36 hours
Hurricanes - the predictable hazards?
Alistair McNaught - 2001
Predictable impacts?Wind * Waves * Rain * Surge
Galveston (Texas) 8 Sep 1900.One of US most prosperous cities - built on island 2 - 3m above sea level.
Hurricane surge = 5m.
Combination of damage to wooden houses -
* Wind damage* Flotation 8000-12000 deaths due to storm surge.
Hurricanes - the predictable hazards?
Alistair McNaught - 2001
Predictable places?Global scale patterns
To make a hurricane take
• warm ocean - 27ºC
• upper atmosphere divergence
• a dash of Coriolis force
Too cool
Too cool
Too little spin
2613 9
6
8 10 60
Hurricanes - the predictable hazards?
Alistair McNaught - 2001
Predictable places?Local scale patterns
To make a hazard take
• A vulnerable location
Coastal plain / Barrier Island Island eg Floyd Sept 99 - USA
River flood plain eg Cyclone Eline Feb 2000
Mozambique
Hurricanes - the predictable hazards?
Alistair McNaught - 2001
Predictable places?Micro scale patterns
To make a hazard take
• A vulnerable location
Sample result
Where to avoid
Hurricanes - the predictable hazards?
Alistair McNaught - 2001
Enter the Unpredictables
Speed of system
The system moves at speeds determined by the energy supply. This depends principally on temperature of sea
A warm sea fuels the hurricane, cooler sea slows it.
But the hurricane may move across warm currents, gaining energy OR may mix the water, altering its potency as a fuel.
Hu
rric
an
e D
en
nis
- S
ep
t 9
9
impact
s on t
he G
ulf S
tream
...
Hurricanes - the predictable hazards?
Alistair McNaught - 2001
Upper atmosphere weatherAccelerator brakes and steering (upper atmosphere weather patterns)
Accelerator (warm water) and brakes (cold water)
Steering
Enter the Unpredictables
Location of landfall
US Weather Service accuracy at predicting landfall location 24 hours before landfall (km from actual landfall site):
Date 1995 1996 1997 1998
Km error134 130 145 140
See Flash movie
Hurricanes - the predictable hazards?
Alistair McNaught - 2001
Enter the Unpredictables
Behaviour of landscape - eg Hurricane Mitch Oct/Nov 1998
Landscape
Relief
Mountainous in region where Mitch stalled
Drainage
Steep, dense networks - 70% roads impassable in Nicaragua after Mitch
Slope stability
Weak volcanic ash
Vegetation
80,000 hectares/yr tropical rainforest
cleared in coastal Honduras
Hurricanes - the predictable hazards?
Alistair McNaught - 2001
Enter the Unpredictables
People
Decision makers
Preparation, planning, warning systems, emergency shelters
Behaviour of people
Communities
Mitch - flooding in Tipitapa alerted by locals, first aid contacts via locals, refugee camp water pipe laid by locals
Individuals
Stay to protect property? Attract aid? Avoid vulnerability?
Hurricanes - the predictable hazards?
Alistair McNaught - 2001
Enter the Unpredictables
Events
Hurricane Mitch - Casitas Volcano produces lahar due to crater lake collapse
Hurricanes - the predictable hazards?
Alistair McNaught - 2001
Conclusions:
More predictable than they used to be; Galveston (Texas) 8 Sep 1900 with 8 - 12000 deaths due to a 5 metre surge at night with no warning wouldn’t happen today.
But prediction does not equate to preparedness. Orissa Cyclone 1999 killed 20,000 people in India. There was a 10-15 metre surge and the cyclone stalled for 8 hours.
But 100,000 people were evacuated before the cyclone hit.
“the dead are mostly daily wage labourers, fishermen and women.”
Poverty is the single biggest predictor of hurricane impact.