Characteristics of storm surge disasters along Fujian coast in recent 10 years

LI Cheng,SHI Xiaoxiao,CAI Renhan,WANG Kaiyue,DING Feng,YIN Jiatong

1.National Marine Data and Information Service,Tianjin 300171,China;

2.The Agricultural Bank of China,Tianjin 300202,China

Abstract: This paper gives the statistics of storm surge disasters which happened along Fujian coast from 2008 to 2017, and analyzes the spatial and temporal distribution of storm surges, economic losses status of storm surge disasters and the characteristics of storm surge disaster. The results show that the storm surge could frequently attack Fujian, affects large domain, and results in severe. What’s more,during the impact of storm surge, the combination of high sea level, astronomical tide and storm surge could increase the disaster level of storm surges.

Keywords:storm surge,disaster,spatial and temporal distribution

1 Introduction

Storm surges are abnormal sea surface elevations caused by strong atmospheric disturbances, such as tropical cyclones (typhoons or hurricanes) and temperate cyclones(including cold wave gales)[1].The loss of life and property damage caused by the increase of water along the coast by storm surge is called storm surge disaster. In China's coastal areas, storm surge disasters occur frequently. From 2008 to 2017, the total economic losses caused by storm surge in China accounted for 86% of the total economic losses from marine disasters, which is the marine disaster causing the most serious economic losses. Fujian, located on the southeast coast of China, is an important region for population,economic and social development.Due to its proximity to the northwest Pacific Ocean, the world's largest source of typhoons, Fujian is frequently hit by storm surges every summer and autumn, causing serious social and economic losses in the region[2].Therefore, it is necessary to analyze the spatial and temporal characteristics, damage degree, and occurrence pattern of storm surge hazards along the Fujian coast to provide support for further storm surge hazard assessment.

2 Spatial and temporal distribution characteristics of storm surges

From 2008-2017, a total of 29 storm surges occurred along the coast of Fujian Province, including 24 storm surges caused by landing typhoons and 5 storm surges caused by not-landing typhoons.Among them, the storm surge occurred 5 times in 2010,the most in the last decade,and all of them were caused by landing typhoons in Fujian,as shown in Fig. 1. Fujian coastal storm surge mainly occurs from June to October, with the most concentrated in July-September,accounting for about 80%.In the past 10 years,the typhoon season in Fujian Province is Jun. 21 to Oct. 23, a total of 124 days, as shown in Fig.2.

Fig.1 Changes in the number of storm surge occurrences

Fig.2 Seasonal variation of storm surge occurrence

From 2008 to 2017,there occurred 24 times storm surge caused by typhoons landing in Fujian Province. From the distribution of typhoon landfall during the impact of storm surge, in addition to Zhangzhou City, cities like Fuzhou City, Xiamen City, Putian City,Quanzhou City, Ningde City all have typhoon landfall records. These are specifically Fuzhou City 6 times, Xiamen City 1 time, Putian City 3 times, Quanzhou City 6 times and Ningde City 8 times, as shown in Fig. 3.According to statistics, the most typhoon landfall locations are Xiapu County in Ningde City and Fuqing County in Fuzhou City,respectively,6 and 5 times.In terms of landfall intensity distribution,as of the end of 2017,no typhoon of super strong level landed in Fujian,and the level of typhoons and below landed 92%of the total, as shown in Fig. 4. The strongest typhoon of landing in Fujian were the 14thstrong typhoon "Moranti" in 2016, when the landing wind was 15, the central wind speed 48 m/s,and central pressure 945 hPa; the 23rdstrong typhoon 'Fet' in 2013 when its landing wind was 14,the central wind speed 42 m/s,and central pressure was 955 hPa.

Fig.3 Spatial distribution of storm surge occurrence

Fig.4 Landfall typhoon intensity distribution

3 Current status of economic losses from storm surge disasters

From 2008 to 2017, storm surge disasters caused serious losses to coastal aquaculture,fishing vessels,roads and embankment facilities in Fujian,as shown in Tab.1.The cumulative area of farmland affected was 151.36 thousand hectares, the area of aquaculture affected was 156.92 thousand hectares, the cumulative length of coastal engineering damage was 479.54 km2, 69,183 houses were damaged, and 13,572 vessels were damaged. The direct economic loss caused by storm surge disaster in Fujian Province was 17.577 billion yuan[3], with an annual average of about 1.76 billion yuan, as shown in Fig.5.The years with annual losses exceeding 1 billion yuan accounted for 60%,and years with annual losses exceeding 3 billion yuan were 2010(3.310 billion yuan),2013(4.506 billion yuan), and 2015 (3.079 billion yuan). In Fujian Province, the annual direct economic losses from storm surge disasters accounted for a higher total national storm surge loss in that year in 2010 (50.3%),2013 (29.2%),2015 (42.4%)and 2016 (40.0%).In 2012 and 2017,storm surge disasters in Fujian Province were less severe.

Tab.1 Statistics of damage caused by storm surge disaster

Fig.5 Direct economic loss caused by storm surge disaster

4 Characterization of storm surge hazards

According to the previous statistical results on the spatial and temporal distribution of storm surge and the current status of its economic losses, the losses from storm surge disasters in Fujian Province were heavy in 2010, 2013, 2015 and 2016. We can conclude that the years with a high number of typhoons and strong typhoon intensity will cause serious economic losses along the coast of Fujian.

In addition, the typical disaster process of mega-storm surges caused by typhoons that had a serious impact on Fujian Province from 2008-2017 are mainly includes: (1)During the impact of Typhoon 1013 Catfish, the abnormally high sea level along the coast of Fujian brought direct economic losses of 2.622 billion yuan, accounting for 79% of the direct economic losses in Fujian Province that year.(2)During the impact of Typhoon 1323 Fet, Fujian Province was affected by 176,200 people, 136,300 people were relocated, 116 houses were collapsed, 351 houses were damaged, 13.87 thousand hectares of aquaculture were affected, 406 fishing boats were destroyed, 1,820 fishing boats were damaged,3.31 kilometers of wharves were damaged,9.29 kilometers of breakwaters were damaged, 9.88 km of seawalls and shore protection were destroyed. The direct economic loss was totally 1.154 billion yuan,accounting for 26%of the direct economic loss in Fujian Province in that year. (3) Typhoon No. 1513 Soudelor brought direct economic losses of 2.390 billion yuan to Fujian Province, accounting for 78% of the direct economic losses in Fujian that year.(4) During the impact of Typhoon Moranti 1614,aquaculture was affected by an area of 4374.71 hectares,lost 75477.24 tons of aquaculture,direct economic loss of 325,531,500 yuan, 153 fishing boats were damaged, direct economic loss of 4.543 million yuan. The direct economic loss of coastal infrastructure was 35.69 million yuan, including 0.5 kilometers of docks, 2.54 million yuan, 1.13 km2of breakwaters, 23.26 million yuan,3.81 km2of seawall berms,9.08 million yuan,1,781 km2of damaged roads,338,000 yuan,other economic losses of 300,000 yuan, and 104.37 hectares of submerged farmland,613,000 yuan.It brought direct economic losses of 762 million yuan to Fujian,accounting for 47%of the direct economic losses in Fujian Province in that year[4].

As shown in Tab.2,these four typhoon-induced mega-storm surge hazard processes were concentrated in Fujian during August-October,which was also the seasonal high sea level period along the Fujian coast, and all of them coincided with the astronomical high tide period. At the same time, the study shows that the prolonged water gain and loss brought by typhoons contribute to a certain extent to the sea level rise in that month. In August 2012, the full month of water gain and loss from six tropical cyclones along the Chinese coast contributed about 14% to the sea level rise in that month, with the largest contribution of 65%at Xiamen station[5].Therefore,we can conclude that sea level rise will raise the base level of storm surge, and during the storm surge period, if it coincides with high sea level and astronomical high tide, the combination of high sea level, astronomical high tide and storm surge will easily form a catastrophic high tide level and increase the degree of disaster.

Tab.2 Typical storm surge disaster process

5 Conclusion

In summary, the coastal storm surge in Fujian for 2008 to 2017 has the following important characteristics:

(a) Storm surges occur frequently in Fujian Province In the past decade, Fujian coastal storm surge occurs every year, a total of 29 times, the maximum annual occurrence of 5 times (2010), mainly concentrated in July-September,the typhoon season long up to 124 days.

(b) Storm surge affects a wide range in Fujian Province. In the past decade, all coastal cities in Fujian were affected by storm surge processes, and the locations with a high number of typhoon landfalls during the storm surge impact were Xiapu County,Ningde City(6 times)and Fuqing County,Fuzhou City(5 times);as of December 2017,no super typhoon landed in Fujian.

(c) Storm surge disaster is heavy in Fujian Province. In the past decade, the direct economic losses caused by storm surge disasters along the coast of Fujian were 17.577 billion yuan. The years with particularly severe losses (annual economic losses exceeding 3 billion yuan)were 2010,2013 and 2015.

(d) Sea level rise will raise the base level of storm surge. During the storm surge impact, if it coincides with the seasonal high sea level and astronomical high tide, the superposition of high sea level,astronomical high tide and storm surge is very likely to form a catastrophic high tide level,increasing the degree of disaster.