recent climate change and trends in global storminess · 2013-11-03 · us tornadoes european...

RECENT CLIMATE CHANGE AND

TRENDS IN GLOBAL

STORMINESS

Talk Structure

Discussion of trends in storminess over

the last 40 years and future projections.

Tropical Cyclones

US Tornadoes

European Winter Storms

Economic and Societal Impacts

Adapted from Munich Re Data

Hurricane Ike Damage

(Galveston Island)

Tropical Storm Allison

(2001) Houston Flooding

Global Temperature Trend

1880-2012

Tropical Cyclones

Background

A tropical cyclone is a warm-centred low pressure

system which is non-frontal, occurs in tropical and

sometimes subtropical waters, and has a closed low

level wind circulation.

During it’s life a tropical cyclone may grow from a

tropical depression to a tropical storm or, if it

strengthens enough, through to a full blown hurricane.

It is wind speed alone which determines the tropical

cyclone’s category.

Regional Occurrence

Structure of a Hurricane

Saffir-Simpson Hurricane Wind Scale

} Major or Intense Hurricane

U.S. Tropical Cyclone Damage 1925-1995(Pielke and Landsea, 1997)

Storm

Category

Winds

(mph)

Surge

(ft)

Mean

Damage($ millions)

Potential

Damage

Percent

Total

Damage

Tropical

Storm (118)40-74 2-3 59 0 2.0%

Hurricane

Cat. 1 (45)74-95 4-5 624 1 8.3

Hurricane

Cat. 2 (29)96-110 6-8 698 10 6.0

Hurricane

Cat. 3 (40)111-130 9-12 2,978 50 35.0

Hurricane

Cat. 4 (10)131-155 13-18 15,358 250 45.2

Hurricane

Cat. 5 (2)>155 >18 [5,973] 500 3.5

US Damage by Storm Category

In the U.S., major hurricanes account for only 21% of hurricane landfalls but 83% of hurricane damage.

2004 Hurricane Season

2005 Hurricane Season

Hurricane Intensity

Webster et al. (2005)

in a paper in Science

show that:

The number of Cat 4

and 5 strength

hurricanes

worldwide has

increased from

about 11 per year in

the 1970s to 18

annually now.

Global Tropical Storm and

Hurricane Numbers (12-month running totals)

Source: http://models.weatherbell.com/tropical.php

Global Hurricane and Intense

Hurricane Numbers (12-month running totals)

Source: http://models.weatherbell.com/tropical.php

Global Accumulated

Cyclone Energy Index (12-month running totals)

Source: http://models.weatherbell.com/tropical.php

Future Projections

• Likely the global frequency of tropical cyclones

will either decrease or remain essentially the

same by 2100.

• Likely increase in tropical cyclone-related

rainfall rates (+3% to +37%, typically +20%

within 100km of the storm centre).

• Some increase in the mean maximum wind

speed of tropical cyclones is likely (+2% to

+11% globally).

Knutson et al., Nature Geoscience, Feb 2010. Tropical cyclones and

climate change.

U.S Tornadoes

Numbers of Strong-to-Violent

(F3-F5) US Tornadoes 1950-2007

No upward trend exists

European Windstorms

European Winter Storms

Porthleven, Cornwall: 4 Jan 1998 (Courtesy, Simon Burt)

European windstorms

caused damages of US $ 2.8

bn per year 1990-1999

Rank as the 2nd highest

cause of global insured

losses after US hurricanes

Dynamics

Most European windstorms are caused by North Atlantic

extratropical low pressure systems.

These systems gain their energy from horizontal

temperature contrasts between cold, polar air masses

and warm, subtropical air masses.

Since the latitudinal temperature contrasts between

these air masses is greatest during winter, the frequency

and intensity of European windstorms peak during this

season as well.

European windstorms occur between October and

March with a peak incidence in January.

Storm tracks are ‘steered’ by the jet stream.

Dynamics (2)

Windstorm Oratia (28th October 2000)

Peak gusts around 100 mph

Central pressure 951mb

(deepest recorded October

low in UK)

Occurred one year after

damaging windstorms

Lothar and Martin struck

France with similar

intensity.

"We have to realise that this almost certainly

has climate change as a contributory cause.“ (Environment minister Michael Meacher)

"We are seeing increasing evidence that climate change

may be impacting on our environment.“

(Environment Agency's head of operations, Archie Robertson)

“The storms and floods we are now seeing will get

more frequent and more severe.”

(Roger Higman, Friends of the Earth)

Why Winter Storm Incidence May

Change

Zonal mean temperature change by 2100

Data Source

Use gridded climate data for the region 35-70oN, 15oW-30oE to

calculate number of days each year during the period (Oct-Mar)

with Storm Force 10 (55+ mph sustained) wind speeds and

seasonal Accumulated Wind Power Index.

Number of Beaufort Force 10

Days over Europe/N Atlantic

Accumulated Wind Power

Index over Europe/N Atlantic

Change in Number of NH Storms

per Winter by 2100

UKMO

OBS

UKTR HadCM2 HadAM3P

depth control Change

2xCO2

control Change

IS92a

CON

1960-

1990

Change

SRES

A2

deep

Pc<970

22.4 18.5 0.4 21.68 6.92

(99%)

32.37 2.38

(99%)

medium

970<Pc<

1000

68.5 79.8 7.2 98.88 -4.82

(99%)

91.73 -3.34

(95%)

shallow

Pc>1000

33.5 39.8 -4.8 44.08 -11.33

(99%)

37.87 -3.69

(99%)

total 124.4 138.1 2.9 164.63 -9.23

(99%)

161.97 -4.66

(99%)

NAO Considerations

+ve NAO -ve NAO

(Figures Courtesy of Martin Visbeck, Columbia University)

NAO Winter Index 1825-2012

(Figure Courtesy of Tim Osborn, University of East Anglia)

Relationship Between Storminess

and NAO (1971-2012 data)

Summary

There is little evidence for any global warming-

induced upward trend in global windstorms over

the last 40 years.

Most recent research suggest little change or a

decrease in storm frequency with a modest

increase in the frequency of the most intense

storms.

The biggest influence on storm-related casualties

and losses, at least in the near future, will come

from natural climate variability.

Questions?