Review on Energy Resilience

O R I G I N A L P A P E R

Assessment of energy supply vulnerability between China and USA

Lan-Cui Liu • Gang Wu

Received: 26 October 2013 / Accepted: 29 January 2014 / Published online: 12 February 2014 � Springer Science+Business Media Dordrecht 2014

Abstract USA and China are the two largest energy-consuming countries, and energy supply vulnerability is a prior topic on energy policy. Then, we develop energy supply

vulnerability assessment index including the sustainability, the stability, the reliability, and

the diversification indicators to assess and compare the change of energy supply vulner-

ability between China and USA based on the data in 2001–2010. We found that the

fluctuations of energy supply vulnerability in China are more than those of USA. In

2001–2006, the index of China’s energy supply vulnerability presented a quick uptrend,

but it presented a slow downtrend in 2007–2010 due to the uncertainty of some indicators;

energy supply vulnerability of USA presented smaller change from 2000 to 2008 because

of the stable and comprehensive energy supply system, but in 2009 and 2010, it became

obviously less than those in other years due to the decline of energy consumption per

capita. Additionally, Chinese energy supply also faces higher maritime transportation and

geopolitical vulnerability than that of USA. The comparisons of the change of energy

supply vulnerability between China and USA show that it is important to develop com-

prehensive energy supply system to reduce the uncertainty of main effect indicators, such

as the control of energy consumption growth, and the diversification of energy supply and

import.

Keywords Vulnerability � Energy supply � Assessment indicators � Energy supply security

L.-C. Liu (&) Center for Climate and Environmental Policy, Chinese Academy of Environmental Planning, Ministry of Environmental Protection of China, 701 Room, Beikechuangye Building, 10 Dayangfang, Beiyuan Road, Chaoyang District, Beijing 100012, China e-mail: [email protected]; [email protected]

G. Wu Management Department of the National Natural Science Foundation of China, Beijing 100085, China

123

Nat Hazards (2015) 75:S127–S138 DOI 10.1007/s11069-014-1071-1

1 Introduction

Energy supply is vulnerable to a lot of unstable factors such as geopolitical risk, price

fluctuation risk, and piracy attacks risk. Therefore, energy supply security is a priority topic

on energy policy agenda worldwide, especially the oil supply security. As the two largest

energy importers in the world, China and USA face with larger energy supply vulnerability

because their energy consumption is huge and they import plenty of oil to meet their

demand. For example, Chinese oil import depends mainly on Middle Eastern and African

countries where unstable political conditions affect crude oil trade. Oil imports from these

regions require long-distance tanker transportation and the crossing of a number of sea

areas with high incidence of pirate attacks. In contrast, USA imported more of its crude oil

from relatively low-risk countries, notably its North American neighbors Canada and

Mexico, which together accounted for 34.0 % of total imports. Furthermore, oil imports

and the dependence on foreign oil of China increased rapidly with economic growth, but

those of USA presented a downtrend (as shown in Fig. 1). Then what are their respective

energy supply vulnerabilities? What difference exists between their evolution of energy

supply vulnerability? To answer these questions, we develop energy supply vulnerability

index, assess, and compare the change of energy supply vulnerability between China and

USA in 2000–2010.

Several previous studies assessed oil vulnerability and energy vulnerability. Ediger and

Berk (2011) implemented a principal component analysis to establish an Oil Import

Vulnerability Index (OIVI) based on four factors: the crude oil import dependence of

primary energy consumption, the crude oil import bill as a share of GDP, non-diversifi-

cation of import sources, and share of oil in total energy imports. Their study evaluated

Turkish oil imports in the period 1968–2007 based on the OIVI approach. Gupta (2008)

assessed the relative oil vulnerability of 26 net oil-importing countries for the year 2004,

0

100

200

300

400

500

600

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

D ep

en d

en ce

o n

f o

re ig

n c

ru d

e o

il (

% )

C ru

d e

o il

im p

o rt

( m

il li

on to

ns )

China's dependence on foreign crude oil

The U.S. dependence on foreign crude oil

Crude oil imports of U.S.

Crude oil imports of China

Fig. 1 China and US crude oil imports and their dependence on foreign oil in 1996–2010

S128 Nat Hazards (2015) 75:S127–S138

123

adopting a principal component approach to integrate the ratio of value of oil imports to

GDP, oil consumption per unit of GDP, and other individual indicators into a composite

index of oil vulnerability. The index introduced by Gupta was able to capture the relative

sensitivity of various economies toward development of the international oil market, with a

higher value in the index indicating higher vulnerability. Gnansounou (2008) provided a

composite index of energy demand/supply weaknesses as a proxy of energy vulnerability

and assessed the energy vulnerability index for some selected industrialized countries. Wu

et al. (2007) developed a risk-index model using portfolio theory to characterize trends in

China’s oil import risks, quantified the diversification index of China’s crude oil imports

over 1996–2004, and explored the relationship between China’s monthly import prices and

Brent spot prices. Energy systems can be vulnerable to climate change, and Schaeffer et al.

(2012) present a review of the impacts that climate change may have throughout the energy

chain and identify current knowledge gaps and areas for future research development.

Bhattacharyya (2009) analyzed the diversity of fuel mix for electricity generation in

selected European countries and investigated how the fuel bill has changed as a share of

GDP between 1995 and 2005. The drivers of fuel-dependence-related vulnerability are

determined using Laspeyres index decomposition. They found that the gas dependence of

the Dutch and Italian systems made them vulnerable but the vulnerability increased in all

countries in recent years. Wu et al. (2009) compared and analyzed the supply, price, and

transport risks of imports of crude oil and petroleum products using portfolio theory and a

diversification index. Lucena et al. (2009) analyzed the vulnerabilities of renewable energy

production in Brazil for the cases of hydropower generation and liquid biofuels produc-

tion, given a set of long-term climate projections for the A2 and B2 IPCC emission

scenarios.

Comparing with the above studies, the current paper focused on the assessment of

energy supply vulnerability change and the comparisons of China and USA in order to

identify the main factors affecting energy supply vulnerability of China. The rest of this

paper is organized as follows. Section 2 describes the selected evaluation indicators and

related data sources. Section 3 discusses the assessment results of the energy supply

vulnerability. Finally, Section 4 gives the limitations and some conclusions.

2 Indicators and data sources

2.1 Assessment indicators for energy supply vulnerability

The vulnerability of a system is the degree to which that system is unable to cope with

selected adverse events. When applying to energy security in long term, a formal definition

is difficult to implement due to the number of possible harsh events and the epistemic

nature of their uncertainty (Gnansounou 2008). Actually, several factors contribute to raise

the concerns about the growing energy supply insecurity, including the current trends in the

evolution of global economy and geopolitical changes; the risk of import (for example,

price risk and transport risk); the strain on oil and natural gas reserves; the concentration of

most of these reserves in unstable regions; local armed conflicts; and so on. Assessing

national energy supply vulnerability is mainly to measure its ability to response emer-

gencies. Therefore, it is helpful to reduce energy supply vulnerability with high supply

capacity (for example, high energy R/P ratio, self-support ratio, storage ratio, and diver-

sification)and low demand pressures (for example, low energy intensity, consumption per

capita, price fluctuation ratio), to a certain extent. In order to assess national energy supply

Nat Hazards (2015) 75:S127–S138 S129

123

vulnerability, we selected four kinds of indicators from two aspects of supply capacity and

demand pressure, which is shown in Fig. 2.

1. Evaluation indicators for the sustainability of energy supply: energy reserve and

production ratio, energy intensity, energy consumption per capita.

2. Evaluation indicators for the stability of energy supply: self-sufficiency ratio, price

fluctuation ratio.

3. Evaluation indicators for the reliability of energy supply: energy reserve ratio, the

diversification index of energy imports.

4. Evaluation indicators of the diversification of energy supply: energy diversification

index.

Firstly, we normalize all the selected indicators and make them positively related to

energy supply vulnerability in the following manner.

The normalization equation of benefit-type indicator is as follows:

X ¼ðXi � XminÞ=ðXmax � XminÞ ð1Þ

The normalization equation of cost-type indicator is as follows:

X ¼ðXmax � XiÞ=ðXmax � XminÞ ð2Þ

Secondly, the composite index for energy supply vulnerability is computed as the root

square of eight relative indicators:

Iv ¼ 1 � P8

i¼1 X 2 i

8

!0:5

ð3Þ

The equations and explanation of evaluation indicators of energy supply vulnerability

are shown in Table 1.

See Table 2 for the variables and explanation of evaluation indicators of energy supply

vulnerability.

Energy R/P ratio

Energy intensity

Energy consumption per capita

Energy self-support ratio

Energy prices fluctuation ratio

Energy storages ratio

Energy import diversification

Energy diversification index

Energy Supply

vulnerability

Fig. 2 The evaluation index of energy supply vulnerability

S130 Nat Hazards (2015) 75:S127–S138

123

T a

b le

1 E

q u

a ti

o n

a n

d e x

p la

n a ti

o n

o f

in d ic

a to

r o

f e n

e rg

y su

p p

ly v

u ln

e ra

b il

it y

E v a lu

a ti

o n

in d e x

E q u a ti

o n

In d ic

a to

r e x p la

n a ti

o n

E n e rg

y re

se rv

e /p

ro d u c ti

o n

ra ti

o R

R = P ¼ P

n i¼ 1

r i x

i R

e se

rv e /p

ro d u c ti

o n

ra ti

o fo

r c o a l,

p e tr

o le

u m

a n d

n a tu

ra l

g a s,

a b e n e fi

t- ty

p e

in d ic

a to

r

E n

e rg

y in

te n

si ty

E I i

n t: ¼

E c o

n : = G

D P

E n

e rg

y c o

n su

m p

ti o

n p

e r

u n

it G

D P

, a

c o st

-t y

p e

in d ic

a to

r

E n

e rg

y c o

n su

m p

ti o

n p

e r

c a p

it a

P c o

n : ¼

E c o

n : = p

o p

u la

ti o

n E

n e rg

y c o

n su

m p

ti o

n p

e r

c a p

it a ,

a c o

st -t

y p

e in

d ic

a to

r

E n

e rg

y se

lf -s

u ffi

c ie

n c y

ra ti

o R

su p : ¼ P

n i¼ 1

s i x

i

s i ¼

i c o

n þ

i e x

p �

i i m

p

i c o

n �

1 0

0 %

T o

m e a su

re th

e se

lf -s

u ffi

c ie

n c y

o f

e n

e rg

y c o

n su

m p

ti o

n ,

m a in

ly fo

ss il

e n

e rg

y ,

a b

e n

e fi

t- ty

p e

in d

ic a to

r

E n

e rg

y p

ri c e

fl u

c tu

a ti

o n

ra ti

o R

r ¼ P

n i¼ 1 x

ir i

T o

m e a su

re th

e fl

u c tu

a ti

o n

d e g

re e

o f

e n

e rg

y p

ri c e s

(i n

te rn

a ti

o n

a l

c ru

d e

o il

p ri

c e s

a d

o p

te d

in th

is p

a p

e r)

, a

c o

st -t

y p

e in

d ic

a to

r

E n

e rg

y st

o ra

g e s

ra ti

o R

se r: ¼ P

n i¼ 1

se r i x

i T

o m

e a su

re th

e sc

a le

o f

e n e rg

y st

ra te

g ic

re se

rv e s

(n a ti

o n

a l

S P

R a d

o p

te d

in th

is p

a p

e r)

, a

b e n

e fi

t- ty

p e

in d ic

a to

r

D iv

e rs

ifi c a ti

o n

ra ti

o o

f e n

e rg

y im

p o

rt s

I d iv : ¼

1 � P

n i¼ 1 x

i

ffiffiffi ffiffiffi ffiffiffi ffiffiffi ffiffiffi ffi

P m j¼

1 d

2 ij

q T

o m

e a su

re th

e d

iv e rs

ifi e d

d e g

re e

o f

e n

e rg

y im

p o

rt (i

n d

e x

o f

c ru

d e

o il

im p

o rt

a d

o p

te d

in th

is p

a p

e r)

, a

b e n

e fi

t- ty

p e

in d

ic a to

r

E n e rg

y d iv

e rs

ifi c a ti

o n

in d e x

C ¼

ffiffiffi ffiffiffi ffiffiffi ffiffiffi ffiffiffi ffi

P n i¼

1 c

2 i

p T

o m

e a su

re th

e d

iv e rs

ifi c a ti

o n

d e g

re e

o f

e n

e rg

y su

p p ly

, a

c o

st -t

y p

e in

d ic

a to

r

Nat Hazards (2015) 75:S127–S138 S131

123

2.2 Data sources

The data of reserves production ratio of coal, oil, and gas, and the data of primary energy

production, imports, exports, and consumption in 2000–2010 are taken from the BP Sta-

tistical Review of World Energy (2001–2011) (BP 2011), China Custom Statistical

Yearbook 1997–2010 (GACC 2010) and China Statistical Yearbook 2011 (State Statistical

Bureau 2011). The data of national strategic petroleum reserves are taken from the news

and reports of energy administration. China’s oil imports of every supply origins in

2000–2002 are taken from the China’s Foreign Economic Relations and Trade Yearbook

(Commerce Department 2001, 2002, 2003), and the data in 2003–2010 are taken from

China Commerce Yearbook (Commerce Department 2004, 2005, 2006, 2007, 2008, 2009,

2010, 2011). The energy intensity and energy consumption per capita data are taken from

the China energy report (2010): energy efficiency research (Wei et al. 2010). The data of

USA are taken from the Energy Information Administration of the US Department of

Energy (EIA 2011).

3 Empirical results discussion and analysis

3.1 The index of China’s energy supply vulnerability presents an uptrend and then

downtrend

The proposed energy supply vulnerability indicators were estimated for the year

2000–2010 to compare the energy supply vulnerability between China and USA. There is

huge difference with the changes of energy supply vulnerability between China and USA

due to the gap of economic development stage and energy supply capacity. The change in

China’s energy supply vulnerability presents on a roller coaster; however, the change in

USA presents a step-by-step downtrend (as shown in Figs. 3, 4). We will discuss and

analyze the detailed reasons leading to the differences, respectively.

In 2001–2006, the index of China’s energy supply vulnerability presented a quick

uptrend, as shown in Fig. 3, mainly due to:

Table 2 Variables and explanation of indicators of energy supply vulnerability

Variables Explanation of variables

Iv Index of energy supply vulnerability

Xi Feature value of indicator i

ri Reserve/production ratio of the ‘‘i’’ fossil energy

xi Share of the ‘‘i’’ fossil energy

Econ: Energy consumption

si Self-sufficiency ratio of the ‘‘i’’ energy

icon:; iexp :; iimp: The consumption, export and import amounts of the ‘‘i’’ fossil energy

ri Variance of the ‘‘i’’ energy price

seri Strategic reserves ratio of the ‘‘i’’ fossil energy

dij Share of the ‘‘j’’ import source for the ‘‘i’’ fossil energy

Ci Share of the ‘‘i’’ energy in primary energy consumption

S132 Nat Hazards (2015) 75:S127–S138

123

1. Energy consumption quickly grew. With the rapid economic growth, China’s energy

consumption increased by average annual speed of 12 %, bringing huge pressure on

energy supply vulnerability. Some southern regions even experienced electricity and

oil supply shortages to some extents.

2. Energy supply sustainability decreased. During this period, the energy reserves/

production ratio rapidly reduced. The reserves/production ratio of coal decreased by

50 %, and the reserves/production ratio of oil decreased by 40 % compared with that

of 2001.

3. The energy imports risk rise. As oil imports kept a rapid increase, the dependence of

import exceeded 42 %. However, China’s oil imports were still overly dependent on

instable Middle East regions, occupying a share of as high as 47 %. The diversification

index of oil imports presents a downtrend. In addition, the international oil price had a

fluctuating increase, intensifying price risk in oil trades.

4. Energy intensity rebounded and the energy consumption per capita rapidly increased.

Before 2000, China’s energy intensity presented a downtrend. But in 2003–2005, it

rebounded, up 10 % compared with that of 2002. Moreover, energy consumption per

capita also increased by 40 % over the same period.

0.0000

0.1000

0.2000

0.3000

0.4000

0.5000

0.6000

0.7000

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

In d

e x

o f

e n

e rg

y su

p p

ly v

u ln

e ra

b ili

ty

Fig. 3 The index of China’s energy supply vulnerability in 2000–2010

0

0.1

0.2

0.3

0.4

0.5

0.6

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

In d e x

o f e n e rg

y su

p p ly

v u ln

e ra

b ili

ty

Fig. 4 The index of US energy supply vulnerability in 2000–2010

Nat Hazards (2015) 75:S127–S138 S133

123

Except for 2008, the index of China’s energy supply vulnerability presented a slow

downtrend in 2007–2010, mainly due to:

1. The growth of energy consumption was less than those in 2001–2006, with an average

annual growth of about 6.7 %.

2. The sustainability of energy supply weakened and the energy reserves/production ratio

declined slightly.

3. The energy import risk was further rising. The international energy price soared with

sharp fluctuation, especially the case in 2008, causing a higher price risk. For this

reason, the vulnerability index in 2008 largely increased (as shown in Fig. 3).

Additionally, the diversification index of China’s oil imports did not increase

simultaneously, which was basically kept at the level of 2005.

4. The energy intensity quickly declined, but the energy consumption per capita

increased rapidly. In 2010, the energy intensity dropped by 16.76 % compared with

that of 2005.

5. At the end of 2008, the Phase 1 of China’s strategic petroleum reserves project was

finished and put into operation, significantly uplifting the energy reserves ratio in 2010

and decreasing the index of energy supply vulnerability to some extent.

3.2 The index of US energy supply vulnerability presents a downtrend

The USA developed the most comprehensive of energy supply system. Based on the

statistical data, US energy resources reserves are richer than China. In 2010, proven

recoverable coal resources reserve was 237.3 billion tons and ranked the top one. Reserve/

production ratio of coal was 241 and can account for 27.6 % of the world. For crude oil,

proven recoverable resources reserve was 309 billion barrels and ranked twelfth in the

world. Reserve/production ratio was 11.3 and can account for 2.2 % of the world. For

natural gas, proven recoverable resources reserve was 7,700 billion cubic meter and ranked

fourth in the world. Reserve/production ratio of coal was 12.6 and can account for 4.1 % of

the world. However, USA is still the biggest energy importing country due to the higher

energy consumption per capita. In 2010, energy consumption per capita was 7.23 toe,

which was almost four times as much as the average energy consumption per capita in the

world.

Figure 4 shows that energy supply vulnerability of USA presented smaller change from

2000 to 2008, but in 2009 and 2010, it became obviously less than those in other years. The

main reasons are as follows:

1. Energy consumption per capita of USA in 2009 and 2010 decreased by 12.56 and

10.24 %, respectively, compared with that in 2000 due to the effects of global financial

crisis since 2008.

2. Energy intensity in 2009 and 2010 also declined obviously, compared with that in

2000, drop by 16.36 and 16.11 %, respectively.

3. Energy self-sufficiency ratio and energy reserve ratio had been improved greatly. In

2000, they were 71.61 and 7.52 %, and increased to 76.56 and 10.61 % in 2009, and

76.05 and 10.40 % in 2010.

4. Energy supply types and energy import sources became more diversified, and the

international oil prices fluctuated less, which can ensure the supply security.

S134 Nat Hazards (2015) 75:S127–S138

123

3.3 The effect of geopolitical risk and transport risk on energy supply vulnerability

between China and USA

Due to data limitation, we have not considered the geopolitical risk and transport risk

among the evaluation indicators. In fact, the geopolitical risk is one of the important factors

affecting energy supply vulnerability, but it is very difficult to quantitative evaluation.

Although China and USA are the two largest crude oil importers in the world, they differ

substantially with regard to their crude oil import sources and geopolitical risks. For

example, China depends mainly on Middle Eastern and African countries where unstable

political conditions affect crude oil trade. Importing from these regions requires long-

distance tanker transportation and the crossing of a number of sea areas with high inci-

dence of pirate attacks (as shown in Fig. 5). In 2010, China’s imported crude oil was

obtained largely from the relatively high-risk Middle East, accounting for 47.1 % of total

imports (as shown in Table 3 and Fig. 5). In contrast, the USA imported more of its crude

oil from relatively low-risk countries, notably its North American neighbors Canada and

Mexico, which together accounted for 34.0 % of total imports (GACC 2011; EIA 2011). It

is clear that China faces much greater geopolitical risks and supplies vulnerability than

USA in its sources for crude oil imports.

From the data of International Maritime Bureau (IMB), there were 443 piracy attacks

incidents in 2010, relative to the 2008 and 2009 increased 51 and 9 %, respectively. We

calculated the average incidence of global piracy attacks over 2005–2010 based on the data

from the IMB and International Maritime Organization (in Fig. 6). Firstly, the statistical

results show that the incidence of piracy attacks in Somalia waters was the highest instead

of the Malacca Straits, because many countries were paying great attention to the Malacca

Straits, and there were more frequent maritime patrols, which forced the pirates to transfer

their activities to other areas. And global piracy attacks present diversified trends and

focused almost exclusively on Somalia waters, Indonesian waters, Malacca Straits, Persian

Gulf, Gulf of Guinea, and Caribbean Sea (in Fig. 6). Secondly, unlike the USA, the vital

ship routes for China’s crude oil imports must traverse the waters of higher incidence of

piracy attacks, for example, Somalia waters, Indonesian waters, and Malacca Straits (as

shown in Fig. 5). Thirdly, in recent years, the incidence of piracy attacks in East Africa and

Fig. 5 Trade flow of oil imports of China and USA and distribution of piracy attacks

Nat Hazards (2015) 75:S127–S138 S135

123

T a

b le

3 S

h a re

o f

m a jo

r c ru

d e

o il

im p

o rt

so u

rc e s

o f

C h

in a

a n

d U

S A

in 2

0 1

0

U S

A C

h in

a

S h

a re

o f

m a jo

r o

il im

p o

rt so

u rc

e n

a ti

o n

s (%

) S

h a re

o f

m a jo

r so

u rc

e re

g io

n s

(% )

S h

a re

o f

m a jo

r o

il im

p o

rt so

u rc

e n

a ti

o n

s (%

) S

h a re

o f

m a jo

r so

u rc

e re

g io

n s

(% )

C a n

a d

a M

e x

ic o

S a u

d i

A ra

b ia

N o

rt h

A m

e ri

c a

C e n

tr a l

a n

d S

o u th

A m

e ri

c a

A fr

ic a

S a u

d i

A ra

b ia

A n

g o

la Ir

a n

M id

d le

E a st

A fr

ic a

2 1

.5 2

1 2

.4 4

1 1

.7 8

3 3

.9 6

1 9

.7 2

2 1

.7 7

1 8

.6 1

1 6

.5 2

8 .8

9 4

7 .1

2 2

9 .6

0

S136 Nat Hazards (2015) 75:S127–S138

123

West Africa has also increased considerably, especially in the Somalia waters and Gulf of

Guinea. For example, the Saudi Arabia-owned supertanker ‘‘Sirius Star’’ hijacked by

Somalia pirates in a raid 450 miles southeast of Mombasa, Kenya, on November 15, 2008.

There were two piracy attacks on Chinese ship in Somalia waters and Gulf of Aden on

November and December 2008, respectively. In order to ensure the transportation security,

the Chinese navy fleet arrived in the Gulf of Aden off Somalia to carry out the first escort

mission against pirates on January 7, 2009. Therefore, Chinese crude oil imports face

higher energy supply vulnerability than that of USA from the perspective of maritime

transportation risk and geopolitics.

4 Conclusions

Based on the assessment for energy supply vulnerability index in China and USA, we

found that the fluctuations of energy supply vulnerability in China are more than those of

USA. In 2001–2006, the index of China’s energy supply vulnerability presented a quick

uptrend, but it presented a slow downtrend in 2007–2010 due to the uncertainty of some

indicators; energy supply vulnerability of USA presented smaller change from 2000 to

2008 because of the stable and comprehensive energy supply system, but in 2009 and

2010, it became obviously less than those in other years due to the decline of energy

consumption per capita. The comparisons of the change of energy supply vulnerability

between China and USA present us that it is important to develop comprehensive energy

supply system to reduce the uncertainty of main effect indicators, such as the control of

energy consumption growth, and the diversification of energy supply and import.

While the above assessment results and analysis have provided us with interesting

insights, it also has some limitations. Due to data limitations, we do not assess quantitatively

the impacts of the geopolitical factor, transport factor, and piracy attacks in the evaluation

indicators on energy supply vulnerability, but we compared the share of major crude oil

import sources of China and USA in 2010 and analyzed the trade flows of oil imports and

piracy attacks incidents, which show clearly that energy supply vulnerability of China is

also higher than that of USA. From the perspective of assessment indicators and method,

there are quite a few areas in which improvements in data and methods are desirable.

Fig. 6 Distribution probability of global piracy attacks during the period of 2005–2010

Nat Hazards (2015) 75:S127–S138 S137

123

Acknowledgments The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China under Grant Nos. 71173207, 70903028, and 71373099. And we would like to sincerely thank for the reviewers helpful suggestions and feedback on an early draft of this paper.

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