High-resolution Regional Climatic Simulations And Projections Of Typhoons And Extreme Rainfall In Eastern China

In this thesis,multiple regional climate models(RCMs)with moderate resolution(10?50km)are employed to simulate the tropical cyclones(TCs)over the Western North Pacific and extreme rainfall in East China during the historical baseline period.Following detailed evaluation and assessment,future projections under climate scenarios are carried out.Considering that the resolution of the RCMs used is inadequate for meso-scale or small-scale severe weather systems,the RCM with relatively good performance is chosen to further drive very high resolution regional climate model(Convection-Permitting Model,CPM,grid spacing ?4 km)to make simulations of the characteristics of land-falling typhoons and extreme rainfall on sub-daily scale in East China.Finally,regarding to changes of land-falling super-typhoons under future global warming,several historical super-typhoons which made landfall are simulated by using CPM with a pseudo global warming(PGW)technique.The mechanism behind changes in TC's intensity,structure and rainfall under future warming is highlighted.The main results are summarized as follows:(1)Most moderate-resolution RCMs are capable of simulating the mean states of TCs over the Western North Pacific,including annual frequency,track and intensity.However,compared with observations,considerable discrepancy does exist,such as weaker intensity,less number and significant lack of super TCs produced.Generally speaking,future projection of the RCMs indicates that the overall annual number of TCs decreases but the number of stronger TCs increases.Additionally,TCs appear to move northward further,showing more TCs at high latitudes.There is a decrease in landfall TCs over South,while an increase in East China.However,large uncertainty exists among RCMs,particularly,in the magnitudes of certain parameters.(2)The characteristics of extreme rainfall events in East China is relatively well reproduced by those moderate-resolution RCMs,including the distribution of annual precipitation,annual raining days,averaged daily rainfall intensity and percentage of extreme precipitation.Future projection shows that averaged daily rainfall intensity and percentage of extreme precipitation increase in the entire East china.The number of rainy days drops in South China(SC),but total annual precipitation and heavy rainfall days increase in North-East China(NEC),North China(NC)and Yangtze River Basin(YRB).The annual longest consecutive dry days decrease in northern China and increase in southern China.However,compared to observations,rather large discrepancy exists in the annual rainy days of NEC,NC and YRB,the annual total precipitation,the heavy rainfall days,the annual longest consecutive rainy days,and the maximum precipitation of five consecutive raining days of all regions.(3)The evaluation of CPM's simulation capability has demonstrated that great added-value is gained by CPM compared to moderate resolution RCM.Very intense TCs can be well reproduced by CPM.The intensity and area average precipitation of land-falling TCs are also very close to observations.The inner structure of TCs,such as eye,narrow eye wall as well as spiral rain belt,are also more reasonably represented by CPM.The representation of the frequency of hourly precipitation,averaged hourly intensity and the timing of maximum precipitation have been significantly improved by CPM.Projection of land-falling TCs and short time scale extreme rainfall show that,the intensity of TC increase with more strong typhoons and super typhoons making landfall in East china.The hourly area averaged precipitation significantly increases during the process of TC making landfall.In the future,annual rainy hours and light rainfall hours decrease,while heavy rainfall hours increase.(4)Five land-falling super typhoons are simulated by using CPM under current climate and future warming climate defined by a PGW approach.The results show that,the intensity and precipitation increase,and the duration also prolongs after TC making landfall.Further analysis illustrates that increased sea surface temperature enhances intensity of TCs,and the warming of upper-level air suppresses TCs through weakening static instability,which has a net effect to intensify TCs.