Reprint 1280

Change in Destructiveness of Landfalling Tropical Cyclones

over China in Recent Decades

Richard C.Y. LI 1, Wen ZHOU 1,

C.M. SHUN & Tsz Cheung LEE

Journal of Climate, vol. 30, p.3367-3379

2017

1 Guy Carpenter Asia-Pacific Climate Impact Center, School of Energy and

Environment, City University of Hong Kong, Hong Kong, China

Change in Destructiveness of Landfalling Tropical Cyclones overChina in Recent Decades

RICHARD C. Y. LI AND WEN ZHOU

Guy Carpenter Asia-Pacific Climate Impact Center, School of Energy and Environment, City University of

Hong Kong, Hong Kong, China

C. M. SHUN AND TSZ CHEUNG LEE

Hong Kong Observatory, Hong Kong, China

(Manuscript received 11 April 2016, in final form 7 January 2017)

ABSTRACT

This study investigates changes in the destructiveness of landfalling tropical cyclones (TCs) over China

during 1975–2014. Using four different TC datasets, it is found that TCs making landfall over east China

(TCEC) have tended to be more destructive in recent decades, with a significant increase in the power dis-

sipation index (PDI) after landfall. Both time series analysis and diagnostic analysis reveal that such an

increase in the PDI of TCEC is associated with concomitant enhancement in landfall frequency as well as

landfall intensity over east China. In contrast, changes in the PDI of TCs making landfall over south China

(TCSC) are less apparent. Examination of different TC-related parameters shows no obvious changes in terms

of landfall frequency, duration, and maximum intensity of TCSC. Diagnostic analysis further suggests that the

reduction in TC occurrence over south China offsets considerably the positive effects of the intensity and the

nonlinear term.

Further examination of the environmental parameters reveals significant changes in the large-scale steering

flow in recent decades, which is characterized by a prominent cyclonic circulation centered over southeast

China. The southeasterly flows on the eastern flank of the cyclonic circulation tend to favor subsequent

landfall of TCs over east China, resulting in an increase in landfall frequency, which contributes in part to the

enhanced PDI of TCs over this region. Meanwhile, the slowing down of the mean translation speed of TCEC

and the weakening of vertical wind shear coupled with warmer SSTs in the WNP tend to favor the in-

tensification of TCEC, leading to an increase in intensity and hence the PDI of TCs over east China.

1. Introduction

China, one of the most densely populated countries in

the world, is adversely affected by tropical cyclones

(TCs). About seven TCs make landfall in China every

year, inflicting huge losses of life and property (Zhang

et al. 2009; Lu and Zhao 2013). During the period 1983–

2006, an average of 472 people were killed each year by

the landfalling TCs, with the greatest casualties occur-

ring in coastal cities in Zhejiang, Fujian, andGuangdong

Provinces (Zhang et al. 2009). Super Typhoon Fred,

landfalling over Zhejiang inAugust 1994; Super Typhoon

Herb, striking Fujian in August 1996; and Tropical Storm

Bilis, invading Fujian in July 2006, are some of the

deadliest TCs that have affected China in recent de-

cades (Zhang et al. 2009). More recently, Super Ty-

phoon Rammasun also wreaked havoc in Hainan

Island, western Guangdong, Guangxi, and Yunnan in

July 2014, resulting in at least 30 deaths and over 26.5

billion renminbi (RMB) direct economic loss (HKO

2015). Throughout the world, TC-induced socioeconomic

losses have also shown a remarkable increase over the

last few decades as a result of population growth, ur-

banization, and climate change (Pielke et al. 2008;

Zhang et al. 2009; Xiao and Xiao 2010). Understanding

changes in the characteristics of landfalling TCs thus

becomes essential for climate change adaptation and

disaster mitigation.

The relationship between climate change and TC ac-

tivity has long been a topic of active research and de-

bate. Based on the power dissipation index (PDI),Corresponding author e-mail: Dr. Wen Zhou, wenzhou@cityu.

edu.hk

1 MAY 2017 L I E T AL . 3367

DOI: 10.1175/JCLI-D-16-0258.1

� 2017 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS CopyrightPolicy (www.ametsoc.org/PUBSReuseLicenses).

several studies have reported a significant increase in the

destructive power of TCs in the western North Pacific

(WNP) and North Atlantic since the mid-1970s

(Emanuel 2005; Webster et al. 2005), which they ar-

gued were induced by anthropogenic warming. By using

the anthropogenic climate change index (ACCI),

Holland and Bruyère (2014) investigated the potential

global warming contribution to global tropical cyclone

activity from 1975 to 2010 and, after accounting for

analysis and observing system changes, found sub-

stantial relationships between ACCI and the observed

increase in the proportion of very intense TCs (Saffir–

Simpson category 4 and 5) in all ocean basins. On the

other hand, other research groups have indicated that

there are still large uncertainties in detecting the human

influence on TC activity in the WNP basin due to the

considerable interdecadal natural variability and the

issues of homogeneity and consistency of TC records

kept by different warning centers (Landsea 2005; Chan

2006, 2008). For future projections of TC activities in

WNP, climate models mostly suggest decreases in TC

frequency but increases in TC intensity and related

precipitation rates in the twenty-first century (e.g., Ying

et al. 2012; Wu et al. 2014; Tsuboki et al. 2015; Knutson

et al. 2015; Walsh et al. 2016). Most of the previous

studies have focused primarily on basinwide TCs; of

these, relatively few have tried to investigate changes in

the properties of TCs after landfall. An increase in TC

activity after landfall is particularly hazardous since

most TC-related casualties occur during this time. A

recent study by Chan andXu (2009) analyzed the annual

frequency of landfalling TCs over East Asia during

1945–2004 but found no obvious trends. Park et al.

(2011), on the other hand, showed that the PDI, as well

as the rainfall of landfalling TCs, has increased signifi-

cantly in recent decades over Japan and the Korean

peninsula. Park et al. (2014) further noted a shift in the

location of maximum intensity of TCs on the East Asian

coastline during 1977–2011 and the potentially growing

threat of TCs over East Asia. Tu et al. (2009) also re-

ported that an abrupt shift in the TC activities in the

vicinity of Taiwan occurred in 2000, mainly due to a

northward shift of the typhoon track over the WNP–

East Asian region. Owing to the vast socioeconomic

influences of landfalling TCs and their uncertain

variation, a comprehensive study is essential to in-

vestigate changes in the destructiveness of landfalling

TCs over China, a topic that has not been examined in

detail in previous studies.

The rest of this paper is organized as follows: section 2

introduces the data and methodology used in this study,

and the climatology and distributions of landfalling TCs

over China are presented in section 3. Section 4

examines the changes in destructiveness of these land-

falling TCs, and section 5 investigates the possible fac-

tors contributing to such changes. Finally, section 6

discusses and summarizes the results.

2. Data and methodology

a. Data

The TC dataset acquired from the Joint Typhoon

Warning Center (JTWC; https://metoc.ndbc.noaa.gov/

web/guest/jtwc/best_tracks/western-pacific) at 6-h in-

tervals is primarily used for investigation in this study

unless otherwise stated. Other best-track datasets from

the Hong Kong Observatory (HKO), the Regional

Specialized Meteorological Center of the Japan Mete-

orological Agency (JMA), and the China Meteorologi-

cal Administration–Shanghai Typhoon Institute (CMA)

were also used to validate our results. Since the maxi-

mum sustained wind speed is recorded differently for

different TC datasets (the JTWC and CMA datasets are

based on 1-min and 2-min sustained wind speed, while

both the HKO and JMA use 10-min sustained wind

speed), an adjustment factor of 1.14 (1.01) was applied

to the HKO and JMA (CMA) datasets for 10- to 1-min

(2- to 1-min) conversion (Knapp et al. 2010; Park et al.

2011; Barcikowska et al. 2012). It should be noted that

using the 10-min sustained wind speed is the World

Meteorological Organization (WMO) recommended

practice for depicting tropical cyclone intensity. The use

of 1-min mean wind as the basis in computing the PDI in

this study is only for the sake of aligning with the original

definition of PDI by Emanuel (2005). It does not have

any implications with regard to the wind averaging pe-

riod practice as recommended by the WMO. We do not

expect that the use of the 1-min wind versus 10-min

mean wind in this study will have significant impact

on the observed trend and the salient findings, as the

conversions between 1-min and 10-min mean winds

involve a linear factor (Harper et al. 2009). To ensure

data reliability, the analysis period of the present study is

restricted primarily to 1975–2014, which roughly corre-

sponds to the period when routine satellite data are

available (Park et al. 2011). Monthly atmospheric data

for the same period were archived from the National

Centers for Environmental Prediction (NCEP)–National

Center for Atmospheric Research (NCAR) reanalysis

(Kalnay et al. 1996), while the monthly National Oceanic

and Atmospheric Administration 28 3 28 Extended Re-

constructed Sea Surface Temperature (ERSST) version 4

data were obtained from the website (http://www.esrl.

noaa.gov/psd/) of NOAA. A landfalling TC in this study

refers to any TC that crosses the coastline of China at

3368 JOURNAL OF CL IMATE VOLUME 30

least once during its lifetime. Although we consider

primarily all the TCs making landfall over China in the

present study, it is worth noting that the results below

will not be affected after excluding those weak tropical

depressions with maximum sustained wind speed less

than 34 kt.

b. Statistical analysis of the potential destructivenessof TCs

One common measure of the potential destructive-

ness of TCs is the PDI, which is defined as the sum of the

cubes of the maximum sustained wind speed over the

entire lifetime of a TC (Emanuel 2005). Since the main

focus of this study is the changes in TC destructiveness

after landfall, the PDI is derived specifically based on

the TCs’ maximum sustained wind speed after landfall.

The annual PDI is then calculated by summing the in-

dividual PDIs over a particular year. Calculated this

way, the annual PDI thus takes into account the fre-

quency, intensity, and duration of landfalling TCs and

can be used to represent the activity and destructive

potential of these TCs.

To further confirm the changes in the annual PDI and

to quantitatively assess the relative contributions of

different incorporated parameters (TC frequency, TC

intensity, and the nonlinearity of the previous two

factors) to the overall PDI changes, an alternative di-

agnostic analysis is also carried out. In this method, the

PDI is recalculated for each 58 3 58 grid cell such that its

value can be expressed in terms of the occurrence fre-

quency (F) and the maximum sustained wind speed (y)

of the TCs in that particular grid. The climatological

PDI (denoted by overbars) for each 58 3 58 grid cell A

can thus be written as

PDI(A)5F(A)3 y3(A) , (1)

where F is the TCs’ occurrence frequency, and y is the

TCs’ maximum sustained wind speed in grid cell A. The

PDI anomaly (denoted by prime symbols), with respect

to its climatology, can then be evaluated as

PDI0(A)5PDI(A)2PDI(A)

5F 0(A)y3(A)1F(A)y30(A)1F 0(A)y3

0(A) .

(2)

Equation (2) consists of three terms, which illustrate the

different contributions of these factors to the overall

changes in PDI. The first term F 0(A)y3(A) reveals the

contribution from anomalous TC occurrence frequency

to the overall PDI changes under the condition that the

maximum sustained wind speed is unchanged. The

FIG. 1. (a) The locations (indicated by the triangles) and the mean frequency (indicated by the contours) of TCs

making landfall in China during 1975–2014, and the associated tracks of (b) TCEC and (c) TCSC. The bold curves in

(b) and (c) denote the mean regression trajectories of TCEC and TCSC.

1 MAY 2017 L I E T AL . 3369

second term F(A)y30(A) represents the contribution

from anomalous maximum sustained wind speed, while

the third term F 0(A)y30(A) is the nonlinear term associ-

ated with changes in both the frequency and maximum

sustained wind. Through such a decomposition, changes

in PDI can be quantitatively decomposed and assessed

in terms of the three factors, namely the frequency effect

(first term), the intensity effect (second term), and the

nonlinear effect (third term).

3. Distribution of landfalling TCs over China

In this section, we will first take a look at the climatic

characteristics of landfalling TCs in China. Figure 1

shows the distribution of landfalling TCs in China during

1975–2014. Following previous studies (Kim et al. 2008;

Li and Zhou 2013), the large territory of China is sub-

divided into southChina (SC) and east China (EC) by an

artificial boundary line along 258N. A total of 211 TCs

made landfall in China during 1975–2014. Of these,

150 TCs (71%) made landfall over SC, while the re-

maining 61 TCs (29%) struck the EC coast. Substantial

differences can also be found in the prevailing tracks of

these two groups of TCs. As shown in Figs. 1b and 1c,

TCs making landfall over SC (TCSC) take mainly a

northwestward track, whereas TCs landfalling over

EC (TCEC) are associated primarily with a recurving

track. Figure 2 further shows the monthly variation in

landfalling TCs in China. On average, the landfalling

frequency of TCs is the highest during June–October,

accounting for 97%of the annual total. Therefore, in the

following, the PDI associated with TCEC and TCSC

during the peak season (June–October) will be in-

vestigated to infer any possible changes in recent

decades.

4. Changes in destructiveness of landfalling TCs inChina

a. East China

Figure 3a first shows the variation in the PDI associ-

ated with TCEC during 1975–2014. Apart from clear

interannual variation, a marked positive trend can be

observed in the PDI time series, with an increase of

1.91 3 105 kt3 decade21, which is significant at 95%

confidence based on the Student’s t test. In other words,

in recent decades, TCs have tended to be more active

and destructive after making landfall over EC. A closer

look at the TC-related parameters suggests that both the

landfall frequency and the mean maximum TC intensity

show noticeable increases during 1975–2014, whereas

the mean duration after landfall reveals no obvious

change (Figs. 3b–d and Table 1). This suggests that the

increase in the PDI of TCEC after landfall might be

closely related to the concomitant enhancement in

FIG. 2. Monthly-averaged frequency of (a) TCEC, (b) TCSC, and (c) their sum during 1975–2014.

3370 JOURNAL OF CL IMATE VOLUME 30

landfall frequency as well as the mean maximum in-

tensity in recent decades.

To further confirm the changes in various TC-

related parameters, the results here have also been

tested and verified using different TC datasets, as

depicted in Fig. 4 and Table 1. Similar to the JTWC,

the HKO, JMA, and CMA datasets depict a signifi-

cant increasing trend in the PDI of TCEC, with a value

of 2.66 3 105 kt3 decade21, 1.97 3 105 kt3 decade21,

and 1.44 3 105 kt3 decade21, respectively. The con-

sistency among different TC datasets suggests that the

observed increase in the PDI of TCEC is robust and

detectable. As for the landfall frequency, a prominent

increase can be observed in both the HKO and JMA

datasets, which is consistent with the results of JTWC.

Meanwhile, all four agencies consistently depict a

marked increase in mean maximum intensity after

landfall, while revealing insignificant trends in the

mean duration of TCEC. Comparisons between dif-

ferent TC datasets similarly reveal a positive trend in

the potential destructiveness of TCEC, which aligns

with an associated increase in landfall frequency and

landfall intensity.

To quantitatively assess the factors responsible for

the overall increase in the PDI over EC, an alternative

diagnostic analysis is also carried out by decomposing

FIG. 3. Variations of (a) PDI after landfall (105 kt3), (b) landfall frequency (number), (c) mean duration

after landfall (h), and (d) mean maximum intensity after landfall (kt) of TCEC during 1975–2014. The

corresponding 40-yr linear trends are indicated by the dashed lines. (e) Associated tracks and landfall

locations.

1 MAY 2017 L I E T AL . 3371

the PDI in each 58 3 58 grid into frequency, intensity,

and nonlinear terms based on Eq. (2). Figure 5a shows

the linear trend of the PDI calculated in each 58 3 58grid for TCEC during 1975–2014. A pronounced posi-

tive trend in the PDI can be found in areas extending

from the ocean to the coastal region of EC, suggesting

an increase in destructiveness of TCs over EC. Such an

increase in the PDI of TCEC can be attributed primarily

to the positive frequency effect over EC, accounting for

43% of the local positive trend in the PDI (Figs. 5b,e).

The positive intensity effect ranks second (41%) and

also contributes considerably to the overall positive

trend in the PDI over EC (Figs. 5c,e). The nonlinear

term, on the other hand, is relatively small and plays

only amarginal role compared with the other two terms

(Figs. 5d,e). The results here further indicate that TCEC

has tended to be more destructive in recent decades,

which is a consequence of increases in frequency as well

as intensity over EC.

b. South China

Compared with EC, changes in the PDI associated

with TCSC appear to be less pronounced. The time

series of the PDI reveals an insignificant trend of

1.65 3 105 kt3 decade21 during 1975–2014 (Fig. 6 and

Table 2). Examination of different TC-related param-

eters also shows no obvious change in terms of landfall

frequency, duration, or maximum intensity of TCSC

(Fig. 6 and Table 2). It should be noted that such results

are still valid even if different TC datasets are used

FIG. 4. Variations and linear trends of (a) PDI after landfall (105 kt3), (b) landfall frequency (number), (c) mean

duration after landfall (h), and (d) mean maximum intensity after landfall (kt) of TCEC based on the datasets of

JTWC, HKO, and JMA during 1975–2014.

TABLE 1. The 40-yr linear trends of the PDI after landfall, landfall frequency, duration after landfall, andmeanmaximum intensity after

landfall of TCEC during 1975–2014. Trends that are statistically significant at 95% and 90% confidence are denoted by two asterisks (**)

and one asterisk (*), respectively.

Trends JTWC HKO JMA CMA

PDI after landfall (105 kt3 decade21) 1.91** 2.66** 1.97** 1.44*

Landfall frequency (no. per decade) 0.30* 0.28* 0.30* 0.23

Duration after landfall (h decade21) 0.52 2.72 2.40 0.77

Mean maximum intensity after landfall (kt decade21) 9.92** 8.62** 9.94** 3.88*

3372 JOURNAL OF CL IMATE VOLUME 30

(Fig. 7 and Table 2). Consistent with the results using

JTWCdatasets, changes in the PDI and other TC-related

parameters are not evident for the HKO, JMA, or CMA

datasets. By decomposing the PDI in each 58 3 58 gridinto frequency, intensity, and nonlinear terms, it is simi-

larly noted that changes in the PDI over SC are not sig-

nificant. The reduction in TC occurrence over SC

contributes negatively to the overall PDI increase in SC

and offsets considerably the positive effects of the in-

tensity and the nonlinear term (Fig. 8). The results here

suggest that changes in the destructiveness of TCSC are

less apparent than those of TCEC.

5. Possible factors contributing to the enhancedPDI of TCs over east China

The previous section has identified an evident in-

creasing trend in the PDI of TCEC, which is associated

with enhanced landfall frequency as well as landfall in-

tensity in recent decades. In this section, we identify and

discuss several factors that may be closely related to the

PDI changes of TCEC in recent decades.

a. Changes in environmental steering flow

As suggested by previous studies (Gray 1979; Chan

2005), variation in TC tracks and landfall positions is

FIG. 5. Linear trends of (a) PDI (105 kt3 decade21) for TCEC and the contribution of the (b) frequency effect,

(c) intensity effect, and (d) nonlinear effect to the PDI trend during 1975–2014. Regions with trends that are

significant at 90% confidence are shaded by dots. (e) The associated percentage contributions of each of the term to

the overall trend in PDI over EC (as indicated by the rectangles).

1 MAY 2017 L I E T AL . 3373

governed predominantly by changes in the environ-

mental steering flows. Figure 9a shows the 40-yr lin-

ear trend of the steering flow (i.e., wind averaged over

850 to 300 hPa) during 1975–2014. The linear trend is

characterized by a prominent cyclonic circulation

centered over southeast China. The southeasterly

flows at the eastern flank of the cyclonic circulation

tend to favor subsequent landfall of TCs over EC,

FIG. 6. Variations of (a) PDI after landfall (105 kt3), (b) landfall frequency (number), (c) mean duration

after landfall (h), and (d) mean maximum intensity after landfall (kt) of TCSC during 1975–2014. The

corresponding 40-yr linear trends are indicated by the dashed lines. (e) Associated tracks and landfall

locations.

TABLE 2. As in Table 1, except for TCSC.

Trends JTWC HKO JMA CMA

PDI after landfall (105 kt3 decade21) 1.65 20.57 0.63 21.26

Landfall frequency (no. per decade) 20.01 20.02 0.27 20.32

Duration after landfall (h decade21) 20.44 0.58 0.92 20.32

Mean maximum intensity after landfall (kt decade21) 0.02 0.45 3.02 1.83

3374 JOURNAL OF CL IMATE VOLUME 30

while the westerly flows at the southern flank tend to

suppress the number of TCs landfalling over SC.

Such a change in the steering flow is one possible factor

leading to the recent increase in landfall frequency over

EC, contributing in part to the enhanced PDI of TCs

over this region. The prevailing track shift due to cy-

clonic circulation anomaly centered over southeast

China was also reported in the studies by Wu et al.

(2005), Lee et al. (2012), and Zhao and Wu (2014).

Based on numerical model results of global warming

experiments, Wu and Wang (2004) suggested that the

warming trend of sea surface temperature would cause

the shift of prevailing TC tracks. Moreover, by using a

singular value decomposition (SVD) analysis and

IPCC AR4 historical forcing runs, Wang et al. (2011)

suggested that the observed shift of TC tracks was

linked to the leading SVD mode of global sea surface

temperature warming and the associated changes in

large-scale steering flows. However, since there are

considerable interannual and interdecadal variations in

the TC tracks in the WNP (Liu and Chan 2008; Choi

et al. 2010), further observations and research will still

be required to understand the influence and contribution

of natural variability and anthropogenic warming on the

TC track changes in the WNP.

b. Weakened vertical wind shear over EC andbasinwide SST warming in the WNP

On the other hand, the increasing intensity of TCEC

might be related to a remarkable reduction in vertical

wind shear over EC (Fig. 9b). The weakened wind shear

helps maintain TC structure, sustains TC intensity, and

inhibits extratropical transition of TCs (Gray 1968; Baik

and Paek 2001; Chan 2008). This was also identified by

Park et al. (2011), who revealed that the weakened wind

shear over this region as a result of the weakening of the

East Asian jet has also contributed to stronger land-

falling TCs over the Korean peninsula and Japan in re-

cent decades. Apart from the favorable dynamic factor

of weakened vertical wind shear, it is also noted that the

SST in the WNP has revealed a significant warming

trend in the recent decades (Fig. 9c) accompanied by

weak cooling in the central Pacific. Such warming in SST

is particularly evident over the northern part of the

WNP and is consistent with that found in the previous

studies (Park et al. 2013, 2014). The basinwide SST

warming in the WNP also provides favorable thermo-

dynamic background for the intensification of TCs in the

WNP. As pointed out previously by Park et al. (2014),

such increasing zonal SST gradient over the tropical

FIG. 7. Variations and linear trends of (a) PDI after landfall (105 kt3), (b) landfall frequency (number), (c) mean

duration after landfall (h), and (d) mean maximum intensity after landfall (kt) of TCSC based on the datasets of

JTWC, HKO, and JMA during 1975–2014.

1 MAY 2017 L I E T AL . 3375

Pacific is also closely linked to the strengthened Walker

circulation, which results in strengthened cyclonic flows

and weakened vertical wind shear along the East Asian

coastline during the recent decades.

c. Reduction in mean translation speed

Apart from the weakened wind shear and the

warmer SST, it is also worth noting that there is a sig-

nificant decreasing trend in the mean translation speed

of TCEC over the open ocean before landfall, while

changes in the mean translation speed of TCSC are less

apparent (Fig. 10). With favorable background of in-

creasing SST (Fig. 9c) and deepening of the 268C iso-

therm across the WNP in recent decades (Park et al.

2013), the slowing down of the mean translation speed

allows TCEC to stay longer over the ocean with warmer

SST and deepened warm mixed layer and favors the

intensification of TCEC, which might also help explain

the increase in TC landfall intensity over EC. Yet the

exact cause of this slowing down of the mean translation

FIG. 8. Linear trends of (a) PDI (105 kt3 decade21) for TCSC and the contribution of the (b) frequency effect,

(c) intensity effect, and (d) nonlinear effect to the PDI trend during 1975–2014. Regions with trends that are

significant at 90% confidence are shaded by dots. (e) The associated percentage contributions of each of the term to

the overall trend in PDI over SC (as indicated by the rectangles).

3376 JOURNAL OF CL IMATE VOLUME 30

speed of TCEC is unknown at present and deserves

further study.

6. Discussion and summary

This study investigates changes in the destructiveness

of landfalling TCs over China during 1975–2014. Using

four different TC datasets, it is found that TCEC has

tended to be more destructive in recent decades, with a

significant increase in PDI after making landfall over

EC. Both time series analysis and diagnostic analysis

suggest that this increase in the PDI of TCEC can be

attributed to the concomitant enhancement in landfall

frequency as well as landfall intensity over EC. In con-

trast, changes in the PDI of TCSC are less apparent.

Examination of different TC-related parameters shows

no obvious changes in terms of landfall frequency, du-

ration, or maximum intensity of TCSC. Diagnostic

analysis further suggests that the reduction in TC oc-

currence over SC offsets considerably the positive ef-

fects of the intensity and the nonlinear term.

Examination of large-scale environmental parameters

reveals significant changes in the environmental steering

flow in recent decades, which is characterized by a

FIG. 9. Linear trends of (a) steering flow (ms21 yr21), (b) vertical wind shear (m s21 yr21), and (c) SST (8Cdecade21)

during June–October 1975–2014. Regions with trends that are significant at 90% confidence are shaded by dots.

FIG. 10. Linear trends of mean translation speed (km h21 yr21) of (a) TCEC and (b) TCSC during 1975–2014.

Regions with trends that are significant at 90% confidence are shaded by dots.

1 MAY 2017 L I E T AL . 3377

prominent cyclonic circulation centered over southeast

China. The southeasterly flows on the eastern flank of

the cyclonic circulation tend to favor subsequent landfall

of TCs over EC, resulting in an increase in landfall fre-

quency, which contributes in part to the enhanced PDI

of TCs over this region. Meanwhile, the slowing down of

the mean translation speed of TCEC and the weakening

of vertical wind shear coupled with warmer SST in the

WNP tend to favor the intensification of TCEC, leading

to an increase in intensity and hence the PDI of TCs over

EC.Wu et al. (2014) found the prevailing TC tracks have

shifted westward significantly in recent decades, which

leads to growing TC influence over east China, while

Park et al. (2013) and Park et al. (2014) have similarly

identified a strengthening in TC intensity in southern

Japan and northeast Asia, which they attributed to the

changes in intensification rate and genesis frequency

over these regions. Through a new approach of di-

agnostic analysis of the PDI, the results of the present

study further substantiate and extend the results of these

previous studies by quantitatively assess the relative

contributions of different factors (TC frequency, TC

intensity, and the nonlinearity of these two factors) to

the overall PDI changes of landfalling TCs over EC and

SC, which helps further enhance our understanding on

the changes in TC destructiveness by spotting out the

key factors contributing to the overall PDI changes in

recent decades.

Overall, this study has highlighted a potential in-

crease in the destructiveness of TCs making landfall

over EC, which is coincident with the corresponding

changes in large-scale environmental factors in recent

decades. It should be noted that although PDI is a

widely adopted parameter for assessing the potential

destructiveness of a storm, it may not fully reflect all

hazardous impacts of TCs, including torrential rain and

storm surge induced by landfalling TCs. Given the

significant socioeconomic impacts of landfalling TCs,

follow-up studies will still be necessary to keep in view

the changes in these TCs and to further explore the

underlying factors and mechanisms by means of nu-

merical experiments, in particular on the connection

between global warming and the shift in the prevailing

track of TCs in the WNP. Moreover, against the

background of global warming and sea level rise, the

risk of extreme weather and storm surge induced by

landfalling TCs to coastal cities should be further in-

vestigated to assist in developing relevant disaster

mitigation and adaptation measures.

Acknowledgments. This research is supported by

National Natural Science Foundation of China (NSFC

41675062).

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