Hurricanes - the predictable hazards? Alistair McNaught - 2001 Overview of lecture Nov 2000 - Nov...

Hurricanes - the predictable hazards?

Alistair McNaught - 2001

Overview of lecture

Nov 2000 -

Nov 2001

Predictable?

Unpredictable?

The year so far?



Predictable times?

Predictable places?

Predictable impacts?



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



Predictable times?Medium term patterns



• upper atmosphere weather

• a dash of Coriolis force

El Niño / La Niña

Antarctic circum-polar wave

Pacific decadal oscillation



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:




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




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.



Predictable places?Global scale patterns



• upper atmosphere divergence

• a dash of Coriolis force

Too cool

Too cool

Too little spin

2613 9

6

8 10 60



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



Predictable places?Micro scale patterns

To make a hazard take

• A vulnerable location

Sample result

Where to avoid



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

...



Upper atmosphere weatherAccelerator brakes and steering (upper atmosphere weather patterns)

Accelerator (warm water) and brakes (cold water)

Steering


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




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




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?




Events

Hurricane Mitch - Casitas Volcano produces lahar due to crater lake collapse



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.

Hurricanes - the predictable hazards? Alistair McNaught - 2001 Overview of lecture Nov 2000 - Nov...

Documents

Transcript of Hurricanes - the predictable hazards? Alistair McNaught - 2001 Overview of lecture Nov 2000 - Nov...