Extreme weather and climate events receive muchattention. For example,the Super Typhoon Haiyan(the strongest tropical cyclone ever recorded in theworld)in November 2013,the extreme heavy rainfallin Beijing on 21 July 2012, and Hurricane S and y inNovember 2012 in the U.S.,all resulted in great lossesof human life and severe property damage. The intensity of extreme tropical cyclones(TCs)is also of greatconcern. Emanuel(1987)used a Carnot cycle model toestimate the maximum possible intensity of TCs overwater due to climate warming. Many studies(e.g.,Emanuel, 2005,2008; Webster et al., 2005; Klotzbach,2006; Elsner et al., 2008)have reported that the maximum TC intensity has increased since the 1970s or1980s. However,the relationship between TC intensity and climate change/global warming remains an openquestion (L and sea, 2005; Pielke et al., 2005). Usingthe best-track data from the Joint Typhoon WarningCenter(JTWC),Chan(2006)found that the quantityof intense TCs over the western North Pacific(WNP)did not increase significantly from 1960 to 2004. However,an increasing trend in the peak intensity and frequency of intense typhoons has been found in theWNP basin from 1975 to 2007,based on the TC trackdata from the JTWC,the Regional Specialized Meteorological Center(RSMC)of Tokyo, and the ShanghaiTyphoon Institute(STI)of the China MeteorologicalAdministration (Wu and Zhao, 2012).

In tropical waters,where TCs are active,due tothe lack of direct observations of pressure and winds,estimation of the maximum potential intensity of TCsis an important aspect of TC research. Miller(1958)presented an estimation method for the lowest pressure of hurricanes based on SST and radiosonde data.Three decades later,Emanuel(1988)developed amodel for computing the maximum intensity of hurricanes based on Carnot’s principle. Holl and (1997)improved the estimation method of Miller(1958);the new method is more dependent on the convective available potential energy(CAPE)of the environmental atmosphere. However,Camp and Montgomery(2001)suggested that the model developed by Emanuel(1988) is more effective than that by Holl and (1997). Yu et al.(2010)presented estimates and changes in the TC potential intensity over various TCbasins using 70-yr forecasts of thermal and dynamicalfactors produced by a global ocean-atmosphere coupled model.

Extreme-value statistical methods based on historical TC intensity data are also an important approach for estimating the maximum intensity of TCs,wherein the Gumbel probability distribution is oneof the most important methods,being recommendedby the International Atomic Energy Agency(IAEA) (Gumbel,1958; IAEA,1981; Emanuel and Jagger, 2010).

TCs that influence China originate mainly fromthe WNP and the South China Sea(SCS). Thus,therehave been a number of studies on the climatologicaldistribution of TCs over these waters(e.g.,Chen and Ding, 1979; Wang,1991; Chen et al., 1999; Wang and Qu, 2007; Yuan et al., 2009; Chao and Chao, 2012). Chen et al.(1999)presented histograms showing theaverage and maximum intensity of TCs l and ing inChina. Yu and Duan(2002)used 35-yr data to analyzethe statistical characteristics of TC intensity changesin the WNP. Li et al.(2004)analyzed the characteristics including the frequency and location of TCsl and ing in China. Wang and Ren(2008) and Wanget al.(2008)presented the overall characteristics ofclimate change with respect to the frequency and intensity of TCs l and ing in and influencing China.

However,there is a lack of studies concerningthe intensity and extreme intensity of TCs influencingChina. Thus,this paper aims to describe TC intensity characteristics based on the best-track TC databy use of the Gumbel probability distribution, and toanalyze the intensity of TCs with 50- and 100-yr return periods, and finally to provide a reference for theestimation of extreme TC intensity.2. Data and methods

The data in this paper are the TC best-track data(including minimum central pressure and maximumwind speed)recorded every 6 h over the WNP(including the SCS and the waters north of the equator and west of longitude 180°)during the period 1949–2011,released by the STI,CMA. Previous studies (Ren et al., 2011; Wu and Zhao, 2012)have compared the differences among best-track datasets issued by the STI,RSMC, and JTWC. Wu and Zhao(2012)showed thatthe TC intensity dataset of the JTWC is relativelymore reliable than the other two datasets,but Renet al.(2011) suggested that each dataset has certainadvantages and it is difficult to draw a conclusion asto which dataset is the best. The main objective ofthis paper is not to compare the three datasets. Giventhat the STI dataset provides TC minimum centralpressure and maximum wind speed every 6 h and hasthe longer sequence,we therefore use this dataset inthe present study.

Ren et al.(2007)defined TCs that influenceChina as those causing precipitation over mainl and China and Taiwan Isl and or Hainan Isl and . Theirpurpose was to study the precipitation distributionproduced by these TCs. In this paper,TCs influencing China are defined as any TC whose center entersany location within a radius of 300 km of China and its surrounding waters. The reason for selecting a radius of 300 km is that the TC radius of surface windof Beaufort force 6 usually exceeds this range (Chen and Ding, 1979), and it is also roughly equal to the2.5°grid distance used in this paper. In addition,the IAEA recommends this radius value to assess theimpact of TCs on nuclear power plants (IAEA,1981). A general purpose of this paper is to study thedifferent-intensity TCs influencing China,hence thedefinition of such TCs is altered from that proposedby Ren et al.(2007).

TCs originating from the WNP basin mainly influence central and eastern China and its surroundingwaters. Therefore,our study area is chosen as(10°–55°N,100°–130°E), and is divided into 2.5° ×2.5°latitude-longitude grids. Moreover,the waters withinthe study area are referred to as the surrounding waters of China.

Based on the 6-h best-track data,statistics related to the number and minimum central pressure ofTCs whose centers enter any grid point within a radius of 300 km are determined, and then the minimumcentral pressures of the TCs are sorted in descendingorder; thus,the lowest and the 95th percentile of thelowest central pressures of the TCs are obtained forthe period 1949–2011.

In order to analyze the distribution of extreme TCintensity,based on the sequence of the yearly lowestminimum central pressure of TCs at each grid point,the minimum central pressure of TCs having different mean recurrence intervals can be obtained by using the Gumbel distribution (Gumbel,1958; IAEA,1981). The minimum central pressure distributions ofTCs with 50- and 100-yr return periods are thus givenin this paper.

The cumulative probability density function ofthe Gumbel distribution is as follows:

P(x)= exp{−exp[−(x−a)/b]},

Different methods can be used to estimatea and b, and this paper uses the Lieblein technique (Gumbel,1958; IAEA,1981),as recommended by the IAEA.The Lieblein technique is widely used for estimatingthe probable maximum intensity of TCs influencingnuclear power plants.

The detailed steps involved in estimating the parameters a and b for each grid point are as follows.First,during 1949–2011,the TCs whose centers enterthis grid point within a radius of 300 km are selected.Next,the yearly lowest minimum central pressure isdetermined among those TCs. Note that the yearlylowest minimum central pressure is not necessarily thelowest minimum central pressure of a TC during itslife cycle. Also,if there is no TC influencing a certaingrid point in 1 yr,we use 1010 hPa to represent theyearly lowest minimum central pressure. Thus,the63-yr sample sequence used to estimate the extremecentral pressure of TCs is established. Finally,theLieblein technique is used to estimate the parametersa and bin the Gumbel distribution.

Accordingly,the probability distribution curve and the st and ard deviation of the TC central pressure are calculated at each grid point, and then theextreme intensities of the TCs with 50- and 100-yr return periods at each grid point are obtained.3. Frequencies of TCs with different intensities

Distributions of the total and annual averagenumber of TCs influencing China and its surrounding waters during 1949–2011 are given in Fig. 1. Tofacilitate the description,distribution of the total TCnumber is mainly described in the text. It should benoted that,as described in Section 2,the total numberof TCs influencing China and its surrounding waters isgenerally different from the literature,e.g.,the number of TCs through the same resolution grid box inthe present study differs from that given by Chen and Ding(1979).

Fig. 1. Total(shaded) and annual average(black solidlines)number of TCs influencing China and its surrounding waters during 1949–2011. Triangles indicate the gridpoints of the typical sites where extreme TC intensity analyses are performed in detail.

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Figure 1 shows that the WNP east of the Philippines and the northern part of the SCS are the twoareas yielding the most number of TCs in China and its surrounding waters during 1949–2011. The maximum number in the SCS is more than 400,while thatin the WNP is more than 450,so the maximum annual average number is greater than 6. Over mainl and China,the total number of TCs decreases fromsoutheast to northwest, and the number in coastal areas is larger than that in inl and areas,while that inthe south is more than in the north. The areas farthest west influenced by TCs include western YunnanProvince and the Hetao area(Yellow River Bend)ofcentral Inner Mongolia,while the most northerly areais Heilongjiang Province. The total number of TCsinfluencing Hainan and Taiwan isl and s is the most(more than 300)for l and areas of China; the total number of TCs influencing the coastal areas of Guangdong Province is the second most(more than 250); whilethe total number of TCs influencing the coastal areasof Guangxi Region and Fujian Province is the third(more than 200).

Overall,the areas influenced by TCs in mainl and China mainly include the “first-ladder” terrain area(three ladders of terrain exist in mainl and China) and the Yunnan-Guizhou Plateau. The total number ofTCs influencing the “second-ladder” terrain area(excluding the Yunnan-Guizhou Plateau)is generally lessthan 10 during 1949–2011. The areas to the westof central and western Sichuan,Gansu, and Qinghaiprovinces have never been directly influenced by TCsfrom the NWP in this 63-yr period.

According to the Grade of TCs developed by theChina Meteorological Administration(National St and ards Committee of China,2006),the total and annualaverage numbers of TCs with different intensities,i.e.,tropical depression(TD),tropical storm(TS),severetropical storm(STS),typhoon(TY),severe typhoon(STY), and super typhoon(SuperTY),are given inFig. 2,based on the maximum wind speed of TCs inthe best-track data. Figure 2 shows that the distributions of the number of TCs with different intensitiesare significantly different.

Fig. 2. Total(shaded) and annual average(black solid lines)numbers of TCs with different intensities during 1949–2011.(a)TD,(b)TS,(c)STS,(d)TY,(e)STY, and (f)Super TY.

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The area influenced by TDs is wider than that influenced by TCs with other intensities, and the number of TDs is the largest among the different TC intensity types. The frequency distribution of TDs presentsseveral high-frequency centers,the two most significant ones of which are the WNP east of the Philippines and the northern part of the SCS,where thenumbers of TDs are more than 150, and the totalnumbers of TCs are also the largest. In the BeibuGulf and its surrounding area,northern GuangdongProvince and southern Hunan Province,the northeastern part of the East China Sea, and the Japan Sea,the numbers of TDs are also high. Guangxi Region,Guangdong Province,southern Hunan Province, and Jiangxi Province are the areas most frequently influenced by TDs in mainl and China,where the numbersof TDs are higher than those in Fujian and Zhejiangprovinces. These areas also appear as a high-frequencytongue extending northeasterly from Guangxi Region and Guangdong Province to Jiangxi Province and southern Anhui Province, and this may be one of thereasons for the higher occurrence frequency of heavyrainfall and short-duration heavy rainfall over these areas (Zhang and Lin, 1985; Chen et al., 2013). Comparing Fig. 1 with Fig. 2a shows that the TCs influencingthe “second-ladder” terrain area of China mainly belong to the TD category,which is consistent with thefact that,after l and fall,TCs weaken rapidly due tothe impact of the underlying surface.

TSs and the TC types with intensities above TSlevel influence only the “first-ladder” terrain area ofChina,the surrounding waters, and the northeasternYunnan-Guizhou Plateau; it is difficult for them to affect the “second-ladder” terrain,with the exception ofthe southeastern Yunnan-Guizhou Plateau. The frequencies of TSs are significantly lower than those of TDs,so are the frequencies of TCs with intensitiesabove the TS level. There are three high-frequencycenters of TSs in China and its surrounding waters,of which the northern SCS is the most significant,followed by two others in the WNP east of the Philip- pines. The largest numbers of TSs occur in Guangdong Province and Guangxi Region of mainl and China—larger than those in Fujian and Zhejiangprovinces. The most northerly area influenced by TSsis Heilongjiang Province; however,the numbers of TSsin eastern North China,western and northern Northeast China,are only 1–5(the annual average numberis about 0.1), and the most northerly areas influencedby greater than 5 TSs are eastern Liaoning Province and eastern Jilin Province.

The STS frequency distribution is very similarto that of TSs. The STSs in the northern SCS havethe highest frequencies,followed by those in the WNPeast of the Philippines; moreover,the numbers of STSsin these two areas are more than those of TSs. TheSTSs influence Guangdong Province and Guangxi Region the most frequently in mainl and China—more frequently than TSs do, and more frequently than in Fujian and Zhejiang provinces. The most northerly areainfluenced by STSs is eastern Heilongjiang Province;however,the numbers of STSs in eastern North China,southern and eastern Northeast China are only 1–5, and the most northerly areas influenced by greaterthan 5 STSs are eastern Liaoning Province and southeastern Jilin Province.

The areas influenced by TYs lie significantly farther south and farther east than those influenced byTDs,TSs, and STSs. The most northerly areas influenced by TYs are Sh and ong Peninsula,southernLiaodong Peninsula,the eastern Bohai Sea, and thenorthern Yellow Sea. The northern SCS is a center of the highest frequencies of TYs. TYs influenceGuangdong Province and Guangxi Region the mostfrequently in mainl and China—more frequently thanFujian and Zhejiang provinces. The numbers of TYsinfluencing Guangdong Province and Guangxi Regionare higher than those of TSs, and almost the same asthose of STSs.

The areas influenced by STYs and SuperTYs aresituated significantly farther south and farther eastthan those influenced by TYs. The most northerlyareas influenced by STYs and SuperTYs reach onlyas far as the mouth of the Yangtze River,the southern Yellow Sea,the southern Korean Peninsula, and the southern Japan Sea. The highest frequency center of STYs and SuperTYs is mainly located in theWNP east of Taiwan Isl and and the Philippines. Thenorthern SCS is influenced by a certain frequency ofSTYs,but a very low frequency of SuperTYs. Taiwan Isl and is the area influenced by STYs with thehighest frequency out of the l and areas of China,followed by Hainan Isl and , and then Guangdong,Fujian, and Zhejiang provinces. Eastern Guangxi,eastern Jiangxi,southern Jiangsu, and southern Anhuiprovinces are also influenced by a certain frequencyof STYs. Taiwan Isl and is also the area influencedby SuperTYs with the highest frequency out of thel and areas of China,followed by Fujian and Zhejiangprovinces; southern Guangdong Province and HainanIsl and are also influenced by a certain frequency of SuperTYs.

Accordingly,in the surrounding waters of China,the area influenced by TDs with the highest frequencyis the WNP east of the Philippines,followed by thenorthern SCS; the area influenced by TSs,STSs and TYs with the highest frequency is the northern SCS; and the area influenced by STYs and SuperTYs withthe highest frequency is the WNP east of the Philippines. This result is consistent with the conclusion of Chen et al.(1999)who indicated that most of thestronger TCs originated over the ocean east of 125°E.

Out of the l and areas of China,Hainan Isl and especially, and also the coastal areas of GuangdongProvince and Guangxi Region,experience the highestfrequencies of TDs,TSs,STSs, and TYs. The areainfluenced by STYs with the highest frequency out ofthe l and areas of China is Taiwan Isl and ,followed byHainan Isl and , and then the coastal areas of Guangdong,Fujian, and Zhejiang provinces. The area influenced by SuperTYs with the highest frequency out ofthe l and areas of China is also Taiwan Isl and ,followedby the coastal areas of Fujian and Zhejiang provinces.

Based on the distributions of TCs with different intensities,we can conclude the following. Theintensities of TCs influencing Inner Mongolia,NorthChina,Northeast China, and Central China do not exceed the TS grade. Those TCs influencing Sh and ong and northern Jiangsu provinces do not exceed the TYgrade. Meanwhile,the areas influenced significantlyby SuperTYs are Taiwan Isl and ,Fujian and Zhejiang provinces,which is consistent with the conclusion obtained by Chen et al.(1999),who showed that l and falling typhoons in Fujian and Zhejiang provinces havestronger intensities.

The minimum central pressure of TCs is morereliable and more representative than the maximumwind speed to characterize TC intensity (Holliday and Thompson, 1979). Therefore,in the following,we usethe distribution of the minimum central pressure ofTCs to analyze the distribution of extreme intensityof TCs that influence China and its surrounding waters.4. Extreme intensity of TCs4.1 Historical extreme intensity distribution

The lowest and the 95th percentile(sorted in descending order)of the lowest minimum central pressures of TCs are used to characterize the extreme intensity of historical TCs at each grid point in China and its surrounding waters during 1949–2011(distributions are shown in Fig. 3). Figure 3 reveals that theextreme intensities of TCs decrease from the southeast to northwest over mainl and China,that TCsover coastal areas are generally stronger than thoseover inl and areas, and that those over the south arestronger than over the north. Yet,the extreme intensities of TCs over the coastal areas of Fujian and Zhejiang provinces are stronger than those over HainanIsl and and the coastal areas of Guangdong Province and Guangxi Region,because Fujian and Zhejiangprovinces are prone to STYs and SuperTYs.

Fig. 3.(a)The lowest and (b)the 95th percentile of the lowest minimum central pressures of TCs during 1949–2011.

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Both Figs. 3a and 3b show that the extreme intensities of TCs over the WNP east of the Philippines and Taiwan Isl and are stronger than those over theSCS. The distribution shows that the lowest minimumcentral pressures of TCs over the WNP east of thePhilippines are less than 880 hPa, and those over thenorthern SCS are only less than 930 hPa; thus,thereis a difference of about 50 hPa. The 95th percentileof the lowest minimum central pressures of TCs overthe WNP east of the Philippines is less than 920 hPa,while that over the northern SCS is less than 960 hPa;this means there is a difference of about 40 hPa, and the difference is slightly lower than that of the lowestminimum central pressures of TCs between these twoareas. This indicates that the difference in the extremeintensities between these two areas is about 50 hPa.

The extreme intensities of TCs over Taiwan Isl and are significantly stronger than those over HainanIsl and . The lowest minimum central pressures of TCsover Taiwan Isl and are less than 900 hPa, and thoseover Hainan Isl and are only less than 930 hPa; thus,there is a difference of about 30 hPa. The 95th percentile of the lowest minimum central pressures of TCsover Taiwan Isl and is less than 930 hPa,while thatover Hainan Isl and is less than 960 hPa,meaning thatthere is also a difference of about 30 hPa. This suggests that the difference in the extreme intensities between these two areas is about 30 hPa.

The lowest minimum central pressures of TCsover the coastal areas of Guangdong Province and Guangxi Region are about 930 hPa, and the 95th percentile of the lowest is about 960–970 hPa. Meanwhile,the lowest central pressures of TCs over the coastalareas of Fujian and Zhejiang provinces are about 910hPa, and the 95th percentile is about 940–950 hPa.This reveals that the difference in the extreme intensities between these two areas is about 20 hPa.The lowest minimum central pressures of TCsare about 930–950 hPa over central Guangxi Region,northern Guangdong Province,eastern JiangxiProvince,northern Zhejiang Province,southernJiangsu Province and Shanghai, and the 95th percentile is about 950–970 hPa. This is because the TCsinfluencing these regions are mainly TYs and TCs withintensities below the TY level.

The lowest minimum central pressures of TCsare about 960–970 hPa over northern GuangxiProvince,western Jiangxi Province,central and northern Jiangsu Province and Sh and ong Peninsula, and the 95th percentile is about 960–980 hPa,because theTCs influencing these regions are mainly STSs,TSs, and TDs.

The lowest and the 95th percentile of the lowestminimum central pressures of TCs are about 970–980hPa over western Sh and ong Province,North China and Northeast China,because the TCs influencing these regions are mainly TSs and TDs. However,thelowest and the 95th percentile of the lowest minimumcentral pressures of TCs are below 970 hPa over eastern Heilongjiang Province,which may be associatedwith the fact that this region is a plain and adjacentto the Japan Sea,meaning that TCs passing over thearea are able to easily gain in strength. However,TCswith this intensity are even weaker than extreme extratropical cyclones,because the extreme intensity ofextratropical cyclones has been recorded at 926 hPa (Wallace and Hobbs, 2006).

Based on the best-track dataset of TCs during1949–2011,the above analyses demonstrate that theextreme intensities of TCs over the WNP east of thePhilippines can be less than 880 hPa; those over Taiwan Isl and are less than 900 hPa; those over thecoastal areas of Zhejiang and Fujian provinces are lessthan 920 hPa; those over Hainan Isl and and the coastalareas of Guangdong Province are less than 930 hPa;those over the inl and areas of Zhejiang,Fujian,Guangdong, and Guangxi are less than 960 hPa; and thoseover the coastal areas north of Jiangsu Province and the inl and areas of China are generally higher than960 hPa.4.2 Extreme intensity estimate

The Gumbel distribution is the probabilisticmethod that the IAEA recommends to estimate theminimum central pressure of probable maximum TCs.In this paper,the distributions of TC intensities with50- and 100-yr return periods estimated by using theGumbel distribution are given in China and its surrounding waters,as shown in Fig. 4. The TCs withintensities of 50- and 100-yr return periods belong toextreme weather and climate events. In China and itssurrounding waters,the spatial distributions of TC intensities with 50- and 100-yr return periods are verysimilar to that of the lowest minimum central pressuresof TCs during 1949–2011,albeit with some differencesin values. Figure 4 also shows that the contours of theminimum central pressure of TCs in the coastal areaare very dense,revealing that TCs weaken rapidly after entering the 500–700-km range of l and .

Figure 4a shows that the minimum central pressures of TCs with a 50-yr return period over the WNPeast of the Philippines are less than 860 hPa; and inparticular,those over part of this area are lower than840 hPa,which are very strong for TCs. In the nextsection,we further analyze their possibilities based onthe physical causes of TC development. It is knownthat the lowest minimum central pressure ever observed in a TC was 870 hPa in the center of TC “Tip”in the WNP in 1979 (Wallace and Hobbs, 2006). Theminimum central pressures of TCs with a 50-yr returnperiod over Taiwan Isl and are less than 890 hPa; thoseover the coastal areas of Zhejiang and Fujian provinces are less than 910 hPa; those over Hainan Isl and and the coastal areas of Guangdong Province are lessthan 930 hPa; those over southern Jiangsu Province,Shanghai,southern and eastern Jiangxi Province,inl and Zhejiang Province,inl and Fujian Province,inl and Guangdong Province, and southern and centralGuangxi Region are less than 960 hPa; those overeastern Sh and ong Peninsula,central Jiangsu Province,southern Anhui Province are less than 970 hPa; butthose over other regions of mainl and China are generally higher than 970 hPa.

Fig. 4.Minimum central pressures of TCs with(a)50- and (b)100-yr return periods.

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Figure 4b shows that the minimum central pressures of TCs with a 100-yr return period over the WNPeast of the Philippines are less than 850 hPa; and inparticular,those over some part of this area are lowerthan 820 hPa,which are stronger than those with a50-yr return period. Meanwhile,those over Taiwan Isl and are less than 880 hPa; those over the coastal areas of Zhejiang and Fujian provinces are less than 900hPa; those over Hainan Isl and and the coastal areas ofGuangdong Province are less than 920 hPa; those oversouthern Jiangsu Province,Shanghai,southern and eastern Jiangxi Province,inl and Zhejiang Province,inl and Fujian Province,inl and Guangdong Province, and southern and central Guangxi Region are less than950 hPa; those over eastern Sh and ong Peninsula,central Jiangsu Province, and southern Anhui Provinceare less than 960 hPa; but those over other areas ofmainl and China are generally higher than 970 hPa.Overall,the minimum central pressures of TCs witha 100-yr return period over the areas of China significantly influenced by TCs,such as Taiwan Isl and ,Hainan Isl and ,Zhejiang Province,Fujian Province,Guangdong Province, and Guangxi Region,are lowerby about 10 hPa than those with a 50-yr return period.4.3 Extreme intensity estimate over typical areas

We choose five typical grid points that are proneto strong TCs: Hainan Isl and (20°N,110°E),coastalGuangdong(22.5°N,115°E),coastal Fujian(25°N,117.5°E),Taiwan Isl and (22.5°N,120°E), and theWNP(17.5°N,127.5°E)(denoted by the triangles inFig. 1)—to estimate the reliability of extreme intensities of TCs obtained by means of the Gumbel distribution.

Based on the best-track dataset of TCs during1949–2011,the fitted Gumbel distributions of minimum central pressures of TCs at the five grid pointsare given in Fig. 5. The solid line is the fit cumulative probability of the Gumbel distribution for theyearly lowest minimum central pressure of TCs during the 63-yr period, and the dashed lines are the st and ard deviations of the fit. Figure 5 suggests that the estimated Gumbel distributions using the Liebleintechnique better fit the distributions of the yearly lowest minimum central pressure of TCs at Hainan Isl and ,coastal Guangdong,coastal Fujian, and TaiwanIsl and ; but for the WNP,there are larger differencesof minimum central pressure of TCs with a 10-yr return period between the fitted and the actual values.Therefore,whether or not the Gumbel distribution issuitable to be used to estimate the extreme intensitiesof TCs over the WNP east of the Philippines needs tobe studied further.

Fig. 5. Fitted Gumbel distributions of minimum central pressures of TCs at five grid points:(a)Hainan Isl and (20°N,110°E),(b)Guangdong Province(22.5°N,115°E),(c)Fujian Province(25°N,117.5°E),(d)Taiwan Isl and (22.5°N,120°E), and (e)the WNP(17.5°N,127.5°E),during 1949–2011. Vertical axis: pressure(hPa); lower abscissa,cumulativeprobability; upper abscissa: the average return periods(yr). The solid skew line is the fitted cumulative probabilityof the Gumbel distribution; dashed lines are the st and ard deviations of the fit; crosses are the yearly lowest minimumcentral pressures of TCs.

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In order to compare the estimates of extreme intensities of TCs using datasets with different timespans,we also obtain the distributions of TC intensities with 50- and 100-yr return periods,estimatedby using the Gumbel distribution based on the besttrack dataset of TCs during 1981–2011(figure omittedhere). The results are basically consistent with thoseobtained based on the 1949–2011 data,although thereare 10–20-hPa differences between the estimates. Thisillustrates that,provided the dataset covers a certaintime span,the estimates of TC intensities using theGumbel distribution are stable based on datasets withdifferent time spans.

Based on the best-track dataset of TCs during1981–2011,the fitted Gumbel distribution of minimumcentral pressures of TCs at the WNP point(17.5°N,127.5°E)is shown in Fig. 6,which fits well with thedistribution of the yearly lowest minimum central pressure of TCs during 1981–2011. However,there aresome differences between Figs. 6 and 5e. This may berelated to the different time spans of the datasets usedin the different figures. Pielke et al.(2005) and Elsneret al.(2008) pointed out that,before the 1970s,thelack of routine satellite data causes historical TC intensity data to possess a certain degree of inaccuracy;however,Chan(2006) reported that,for the 1960s,given that some aircraft reconnaissance data of TCsover the WNP are available,the reliability is relativelyhigh.

Fig. 6.As in Fig. 5e,but for the fitted Gumbel distribution of minimum central pressures of TCs at the WNPpoint(17.5°N,127.5°E)during 1981–2011.

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Emanuel(1987)estimated the probable maximum TC intensity(PMTI)over various TC basins using the Carnot cycle. He found that,assuming a seasurface relative humidity of 78%,a thermodynamic efficiency ofε= 0.33, and SST = 32℃,the PMTI is 849or 829 hPa when the SST is 33℃. Furthermore,thePMTIs given by Emanuel(1987)when the SST is 32or 33℃are roughly equal to the TC intensities with50- and 100-yr return periods over the WNP east ofthe Philippines given in this paper using the Gumbeldistribution. In August,the mean climatological SSTover the WNP is about 29℃, and does not exceed 30℃.The SST over the tropics and subtropics has increasedby an average of 0.2℃over the past 50 years (Pielke et al., 2005). Assuming the current extreme SST overthe WNP east of the Philippines is up to 30℃, and SST increases by 0.5℃every 50 years,it will thereforetake 300 yr for SST to reach 33℃.Accordingtotheestimates given by Emanuel(1987),the PMTI for SST=33℃is roughly equal to the intensity with a 100-yrreturn period over the WNP east of the Philippinesgiven in this paper by using the Gumbel distribution.Thus,if the estimates given by Emanuel(1987)aremore accurate,the TC intensities with 50- and 100-yrreturn periods over the WNP east of the Philippinesare overestimated in this paper, and similar conclusions can also be obtained from the differences betweenthe fitted Gumbel distribution and the actual valuesin both Figs. 5e and 6. It should be noted that thefitted Gumbel distribution overestimates the extremeTC intensities over the WNP east of the Philippines,but its intensifying trend of the extreme TC intensities with longer return periods agrees with that of theactual TC intensities.4.4 Classification of areas influenced by TCs

Based on the analyses in Sections 4.1 and 4.2,there are larger differences in extreme intensity of TCsover different areas of China and its surrounding waters,so the areas can be classified according to thesedifferences(Fig. 7).

Fig. 7. Classification of areas based on the minimumcentral pressures of TCs with a 50-yr return period.

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The extreme-intensity TCs over the WNP east ofthe Philippines are the strongest in China and its surrounding waters, and the historical lowest minimumcentral pressure of TCs is below 880 hPa; and thosewith 50- and 100-yr return periods are also lower than880 hPa. According to the estimates given by Emanuel(1987),TCs with a minimum central pressure of 880hPa have maximum wind speeds of up to 80 m s⁻¹,approximately.

The extreme-intensity TCs over Taiwan Isl and areonly weaker than those over the WNP east of thePhilippines, and the historical lowest minimum central pressure of TCs is below 900 hPa. Those with 50- and 100-yr return periods are lower than 890 hPa, and TCs with a minimum central pressure of 890 hPa havemaximum wind speeds of up to 79 m s⁻¹,approximat ely (Emanuel,1987).

The historical lowest minimum central pressureof TCs over the coastal areas of Zhejiang and Fujianprovinces is below 920 hPa. Those with a 50-yr returnperiod are lower than 910 hPa, and those with a 100-yr return period are lower than 900 hPa. TCs witha minimum central pressure of 900 hPa have maximum wind speeds of up to 75 m s⁻¹,approximately (Emanuel,1987).

The historical lowest minimum central pressure ofTCs over Hainan Isl and ,the coastal areas of Guangdong Province, and the northern SCS is below 930hPa,while those with a 50-yr return period are lowerthan 930 hPa, and those with a 100-yr return periodare lower than 920 hPa.

The historical lowest minimum central pressure ofTCs is below 960 hPa over southern Jiangsu Province,Shanghai,southern and eastern Jiangxi Province,inl and Zhejiang Province,inl and Fujian Province,inl and Guangdong Province, and inl and Guangxi Region,while those with a 50-yr return period are lowerthan 950 hPa, and those with a 100-yr return periodare lower than 950 hPa.

The historical lowest minimum central pressure ofTCs is generally higher than 960 hPa over the coastalareas north of central Jiangsu Province and other inl and areas of China,while those with a 50-yr returnperiod are higher than 950 hPa, and those with a 100-yr return period are higher than 940 hPa.

Accordingly,the classification of areas is given inFig. 7,based on the distribution of the minimum central pressure of TCs with a 50-yr return period.5. Conclusions and discussion

Extreme weather and climate events frequentlycause serious casualties and adverse social impacts.Based on the best-track TC data over the WNP during 1949–2011,the distributions of different intensities and extreme values of TCs influencing China and itssurrounding waters are obtained in this study,by using the Gumbel distribution. By doing so,we havecontributed to addressing the lack of research on theclimatological distribution of extreme-intensity TCs, and we thus also provided a reference for estimating the probable maximum intensities of the TCs affectingChina.

We found that different areas of China and itssurrounding waters are influenced by the TCs withdifferent intensities. TDs have the highest frequency and influence the widest area. STYs and SuperTYshave the highest frequency in the WNP east of thePhilippines. Of the l and areas of China,SuperTYshave the highest frequency in Taiwan Isl and ,followedby the coastal areas of Fujian and Zhejiang provinces. Meanwhile, STYs have the highest frequency in Taiwan Isl and ,followed by Hainan Isl and , and then thecoastal areas of Fujian and Zhejiang provinces. TSs,STSs and TYs have their highest frequencies in thenorthern SCS. TDs,TSs,STSs and TYs have theirhighest frequencies in South China. It is difficultfor TSs and TCs with intensities above the TS levelto influence the “second-ladder” terrain area(withthe exception of the southeastern Yunnan-GuizhouPlateau) and other inl and areas of China.

According to the differences of extreme TC intensities in different areas of China and its surroundingwaters,a classification of areas influenced by TCswith different extreme intensities has been presented.Over the WNP east of the Philippines,the TC intensities with 50- and 100-yr return periods are lowerthan 880 hPa and more than 80 m s⁻¹in terms oftheir maximum wind speed. Over Taiwan Isl and ,theTC intensities with 50- and 100-yr return periods arelower than 890 hPa and have maximum wind speedsof more than 79 m s⁻¹. Over the coastal areas ofZhejiang and Fujian provinces,the TC intensity witha 50-yr return period is lower than 910 hPa and islower than 900 hPa with a 100-yr return period. OverHainan Isl and ,coastal Guangdong, and the northernSCS,the TC intensity with a 50-yr return period islower than 930 hPa and is lower than 920 hPa with a100-yr return period. Over southern Jiangsu Province,Shanghai,southern and eastern Jiangxi Province,inl and Zhejiang Province,inl and Fujian Province,inl and Guangdong Province, and inl and Guangxi Region,theTC intensity with a 50-yr return period is lower than960 hPa and is lower than 950 hPa with a 100-yr return period.

Although the Gumbel distribution has beenwidely used in extreme estimates,there is a largedifference of TC intensity between the fitted Gumbeldistribution and the actual one over the WNP east ofthe Philippines. Therefore,whether or not the Generalized Extreme Value(GEV)distribution,which hasbeen applied more widely,can be used to estimate extreme TC intensities over this region requires furtherstudy.

Acknowledgments.Thanks go to China Typhoon Network(www.typhoon.gov.cn)of ShanghaiTyphoon Institute of the China Meteorological Administration for providing “CMA-STI Best TrackDataset for Tropical Cyclones over the Western NorthPacific.”