Study On The Changes Of Land-falling Tropical Cyclone Intensity In The Western North Pacific Over The Past 40 Years

Tropical Cyclones?TCs?are one of the most devastating and common disaster types on the Earth,causing severe losses of life and property and having significant social and economic impacts around the world.Therefore,any variability in the intensity of TCs related to climate change are of great interest to the long-term forecast of TC activity and protect people's lives and property from TC disasters.In this paper,we use the TC best track data from JTWC?Joint Typhoon Warning Center?and ERA-Interim reanalysis data to examine the changes of land-falling tropical cyclone intensity in the western North Pacific?WNP?over the past 40 years.According to the statistical results,the frequency of land-falling TCs in the western North Pacific has not changed much in recent decades,while the land-falling intensity?LFI?,lifetime maximum intensity?LMI?,and destructive potential?as quantified by the Power Dissipation Index,PDI?have increased by 8%,9%,and 33%in the past 40 years,respectively.There exists big differences in the land-falling TC activity form at different months,the land-falling TCs in the WNP occurred most frequently from July to November,about more than 80%of the total number of the year,and the integrated intensity of land-falling TCs are relatively large during this period.In addition,abrupt intensity changes of land-falling TCs are more likely to occur in stronger systems.RI and RD cases occur most in TYs,and most of them intensify with a?V₂₄ in the range of 15–20 m s^-1,or decay with a?V₂₄ in the range of-20 to-15 m s^-1.East of the Philippine Islands?10°–15°N,130°E?is the region with the most frequent occurrence of RI cases,while such cases rarely occur in the South China Sea.By analyzing the trend of the land-falling typhoon LMI in the WNP Basin,it is found that a regime shift in the LMI of land-falling typhoons took place around 2002,and the land-falling typhoon LMI has a considerable increasing trend in the P2 period?2002-2018?,which primarily results from the significant increase in relative proportions of intense typhoons?Category 4-5?and decreased percentages of category1-3 typhoons.The recent increase in the typhoons LMI can also be attributed to the increased number of RI typhoons?79%are intense typhoons?and the decreased count of non-RI typhoons?91%are CAT1-3 typhoons?during the P2 period.Meanwhile,the total number of land-falling typhoons are unchanged.It is the western migration of main development regions that are favorable for typhoon genesis and intensification lead to an increase in the number of RI typhoons,and thus the probability of such typhoon making landfall increases.It is worth noting that not only the number of intense typhoons has increased recently,but also the intensity have strengthened,such extreme changes will threaten the coastal areas of East Asia and Southeast Asia.Under the current climate warming background,the LMI of RI land-falling typhoons over the WNP has increased significantly in recent decades,which can be mainly attributed to the enhanced TCHP in the P2 period.The increases in TCHP may contributed positively to the typhoon intensification,by limiting the negative feedback from typhoon's self-induced because of ocean cooling.In addition,the increased midlevel relative humidity and reduced vertical wind shear are conducive to typhoon genesis and intensification;the strengthened geopotential height also explains the increased number of RI typhoons.Furthermore,the changes in these factors are tied to an overall warming of the upper ocean over the main development regions since the late 1990s,which is large enough to maintain a positive SSTA and provide extra energy to keep positive TCHP anomalies for the typhoon intensification.