The Characteristic And Analyzing Of Disastrous Rainstorm Influenced By Terrain In Guangxi Province

Based on the climate background of global warming in recent years,climate anomalies caused by El nino and La Nina phenomenon,severe weather appeared frequently.It's a serious threat to human's life and property caused by a sudden rainstorm which leaded meteorological disasters and secondary disasters.Guangxi Province located in west of southern China,mountains and hills distributed widely.Influenced by the southwest warm moist airflow,tropical cyclones and cold air mass, the rainy season in Guangxi Province lasts long and the rainfall is plentiful,it is the main source region that occurrence and development of mesoscale heavy rain in south China.Besides,the complicated topographic features of Guangxi had a great influence on precipitation which made an uneven space-time distribution of rain.That's why Guangxi is often stricken by rainstorm and flood disasters frequently,and it's a hotspot of disastrous rainstorm in China.On the ground of applied physical geography,statistics,disaster science and atmospheric science theory,the data of this thesis are analyzed through GIS and MICAPS.Based on a total of 30 years meteorological data collected from1981-2010,we summarized the spatial and temporal distribution of rainstorm and heavy rainstorm successfully in Guangxi Province.Using GIS to carry out a correlative analysis on rainstorm and taking topography as a factor,the thesis discusses about how rainstorm disasters are influenced by terrain factors of Guangxi Province.The typical rainstorm happened on May 18-20,2015 in northeast of Guangxi is selected as a case study to explore forcing effect of terrain factors on disaster rainstorm.To analyze the formation mechanism of the rainstorm from the aspects of circulation pattern,physical quantity,satellite and radar data.Emphatically discusses the terrain factors on the force effect of the heavy rain process.In order to verity the effect of uplifting forced by terrain,we designed a sensitivity test based on the WRF model.The main conclusions of research were as listed as follows:(1)Affected by topography,there are 4 high value regions of rainstorm in Guangxi.The first one lies in southern coastal areas around shiwan mountains winding from Dongxing,Fangcheng to Qinzhou.The second one is located in the east side of dayao mountain,where is centered by Zhaoping,with Jinxiu and Mengshan around.The third one is from the yuecheng-tianping mountain to the southeast yuanbaomountain,with Yongfu as the center and surrounded by Guilin,Rong'an and Liucheng.The forth one starts from Du'an to Donglan,Bama and Fengshan around.Torrential rain mainly occurred in 2 areas:first one located in the coastal from Fangcheng to Qinzhou and Beihai.Another one located in the northeast of Guangxi such as Guilin and Liuzhou.The reason why heavy precipitation occurred frequently in the high value regions is in addition to the local climate factor,weather condition and related system,terrain convergence and the effect of uplifting forced by windward slope is the main reason of the heavy rain increase.(2)In order to diagnose the formation and development mechanism of the rainstorm,the typical rainstorm happened on May 18-20,2015 in northeast of Guangxi is selected as a case.The results show that:The eastward moving upper trough,the low-level vortex sheared,the low-level south westerly jet stream,frontal surface and convergence line corresponding to the southward invading cold waves are the main effective systems,it provides important power condition and trigger mechanism for the disastrous rainstorm;The relatively deep wet layer in northeast of Guangxi,the accumulation of a large number of unstable energy and a steady southwesterly jet stream of water vapor transmission,it provides important heat and moisture conditions;Complex terrain and topography in northeast of Guangxi also play an important role for the produce of the disastrous rainstorm;The effect of uplifting forced by windward slope and terrain convergence of the bell mouth,that is the important triggering factors for the occurrence and development of mesoscale heavy rain in warm area and point reasons for the increase of the rainstorm.(3)In order to study deeply the effect that topographic forcing on the increase of the rainstorm,the typical disastrous rainstorm happened on May 18-20,2015 in northeast of Guangxi is selected as a case.Using WRF model to test the sensitivities of yuecheng mountains and haiyang mountain,the result shows that:The 24 hours precipitation by controlled whether strong precipitation area or rainstorm center are consistent with observed.When reduced the altitude of yuecheng mountains and haiyang mountain to the quite height of surrounding terrain(reduced 600 m and 300 m respectively),the effect of uplifting forced by terrain was small or even disappeared,the overall precipitation decreased whole,the center of strong precipitation also reduced significantly than control.When elevated the altitude of yuecheng mountains and haiyang mountain to the double height respectively,the gradient became steep,on the windward slope side of the mountains,the effect ofuplifting forced by terrain strengthened significantly.Besides,the low-level southwest warm-moist airflow was accumulated due to mountains blocked,the sky of region accumulated a lot of unstable energy,the atmospheric instability increased significantly.Accordingly,the overall precipitation of the test area increased whole,the center of strong precipitation also increased from one to three,the precipitation of the strongest rainfall center increased by a third better than the strong center of the control experimental zone.It is visible that the effect of uplifting forced by terrain and the accumulation of unstable energy strongly.