Path Classification And Risk Study Of Tropical Cyclone Affecting China's Coastal Areas

Global warming will cause changes in the intensity and path of tropical cyclone activity.The rapid urbanization process in coastal areas increases the exposure of disasters.The threat of tropical cyclone disasters cannot be ignored.In this study,China's coastal areas were used as research areas.Based on historical tropical cyclone path data and daily weather station monitoring data,quantitative clustering and risk assessment of tropical cyclones affecting the study area were carried out.The main research contents and research results are as follows:(1)The tropical cyclone intensity(maximum wind speed and energy)in the study area showed a general trend of weak decline between 1949 and 2017.However,in the past 20 years,the landing frequency,maximum wind speed and energy of tropical cyclones showed a significant upward trend.(2)Based on the tropical cyclone path,the K-Means model was used to quantitatively cluster 1000 tropical cyclones in the 1949-2017 impact study area,which were divided into 4 types:Class A tropical cyclones accounted for 18.4%of the total,with an average starting point in the eastern part of the Philippine Sea and an average destination in Hokkaido,Japan.The average path length is 5060.9km,which is a typical steering path.It changes from southeast-northwest to southwest-north,and the turning point is near 126°E28°N.It is far from the coastline and the journey is basically the same.Mainly affecting the northern part of the study area by rubbing.Class B tropical cyclones accounted for 33.6%of the total,with the average starting point in the westernmost part of the Philippine Sea and the average ending point in the eastern part of the Beibu Gulf in the South China Sea.The average path length is 1972.2km,which is a typical straight path with the direction of South East-North West.The southern part of the study area is mainly affected by direct landing.Class C tropical cyclones accounted for 25.6%of the total,with an average starting point in the central part of the Philippine Sea and an average ending point in the eastern side of Zhejiang Province.The average path length is 2750.8km,which is the turning path.It changes from southeast-northwest to southwest-north-east,and the turning point is near 121°E28°N.The distance before turning is much larger than that after turning.The impact range is large,almost throughout the study area,with the central part of the study area being the most concentrated.Class D tropical cyclones accounted for 22.4%of the total,with an average starting point between the Northern Mariana Islands and the Caroline Islands in the western Pacific,with an average destination in southern Fujian Province,China.The average path length is 4221.1km,which is a straight path,and the direction is South East-North West.Most of them directly landed in the study area,and the main area of influence was the southern part of the study area.(3)Based on the wind-rain factor weighted superposition model,the risk of tropical cyclone in the main provinces of the study area from 1985 to 2015 was evaluated.The results show that:The risk distribution generally shows a trend of decreasing from the coastline to the inland.The high value areas are distributed in coastal areas except Jiangsu and Shanghai.From the perspective of the composition of wind and rain factors,the overall north of Fujian,Zhejiang,Shanghai and Jiangsu are dominated by wind factor risk,while the southern Guangdong,Guangxi and Hainan are dominated by rain factor risk.From the perspective of path types,the dangerous high-value areas of Class A tropical cyclones are mainly distributed in the southeastern part of Jiangsu Province,Shanghai and the eastern part of Zhejiang Province.The high-risk areas of Class B tropical cyclones are mainly distributed in Hainan Province,the south of Guangxi and Guangdong,and parts of the eastern coast of Zhejiang Province.The high-risk areas of Category C tropical cyclones are distributed in coastal areas of Hainan Province and Guangxi,Guangdong,Fujian,and Zhejiang.The dangerous distribution of Class D tropical cyclones is similar to that of Class C,except that the risky high value areas are closer to the shoreline.From the perspective of dynamic changes,the risk in 1985-1995 is relatively moderate,and both positive and negative anomalies are distributed.In 1995-2005,the risk anomaly area was significantly reduced,and the abnormal value became lower.There was a significant increase in the risk in 2005-2015,and most negative anomalies became positive anomalies.In general,the tropical cyclone risk in the past 30 years experienced a sharp increase after a small decline.As a basic study of tropical cyclones,path classification is an important way to study the characteristics and dangers of tropical cyclones,and it is of great significance to understand the climate characteristics and changes of tropical cyclones.As a quantitative clustering model,the K-Means model compensates for the defects of the previous subjective recognition methods to some extent.The assessment of tropical cyclone risk is an important part of disaster prevention and mitigation.The study of tropical cyclone risk in China's coastal areas from the three dimensions of path type,hazard factor type and time has not only supplemented the incomplete research of previous studies in the region.It is also an urgent requirement in the context of global change.