Study On The Variation Characteristics Of Extreme Precipitation Events In Shaanxi Over The Past 50 Years

This thesis mainly based on Shaanxi 78 countries routine meteorological station from 1961 to 2013 daily precipitation data,using statistical methods of extreme precipitation events analysis,the climate change of extreme precipitation in the flood period,temporal and spatial variation characteristics of were in-depth study;also Xi'an routine meteorological station 2006-2015 flood hourly precipitation data,using MICAPS data of Xi'an in recent ten years,short-time strong rainfall atmospheric circulation background were classified based on established Xi'an short-time strong precipitation potential forecast equation,and the analysis is validated by a case.This paper is sponsored by the Shaanxi Provincial Meteorological Bureau's science and Technology Innovation Fund Project(project number: 2013M-7).The main conclusions of the study are as follows:(1)During flood season in Shaanxi Province threshold of extreme precipitation spatial distribution characteristics and strength are basically the same,Qinling and most southern site threshold higher than average,to most of the site north of below average,which,in Guanzhong area,the threshold is relatively close,Northern Shaanxi threshold distribution from east to West decreases;extreme precipitation frequency is from south to North reduced;in most area of Shaanxi Province,a day maximum precipitation in more than 100 mm.Among them,one-day precipitation larger sites mainly distributed in Qinling Mountains of southern and Northern Shaanxi.(2)Extreme precipitation events in Shaanxi monthly changes greatly,up to July,accounting for 30% of the total number of extreme precipitation events,followed by August,at least in May,accounting for 7% of the total number of extreme precipitation events in flood season in Shaanxi;interannual and interdecadal changes in the larger,less in 1960 s,after the middle of the 70 s increase in early 80 s increased after 90 s decreased,and increased gradually after twenty-first Century,in recent years increased significantly;extreme precipitation events in southern Shaanxi Guanzhong,annual and decadal changes and the trend is basically the same,the extreme precipitation events in 2011 were 53 A in most years,interannual and decadal variation of Northern Shaanxi differences,extreme precipitation events occurred in the beginning and middle term of 1960 s and 2010 s,other times,relatively few.Extreme precipitation events occurred in September 2011 amounted to 250 times the most.(3)Overall,the flood season in Shaanxi temporal and spatial changes of extreme precipitation distribution has the following characteristics: firstly,extreme precipitation amount and precipitation events occur the change in the number of trend is consistent.Among them,most parts of Northern Shaanxi the trend of decrease,central and west of Guanzhong and southern Shaanxi Eastern is an increasing trend,the west of Southern Shaanxi Micangshan area to decrease,Eastern Guanzhong for weak decreasing trend;secondly extreme precipitation events in the province was affected by the mutations influence in southern Shaanxi larger,1979 and the abrupt change of extreme precipitation increases,1984,it reached significant level;extreme precipitation intensity by Guanzhong influence is big,in 2002 the increase in saltation,in 2013 reached significant level.The frequency of extreme precipitation in the province had no obvious saltation;thirdly the partition of extreme precipitation events are multi time scale features,Shaanxi,Guanzhong large scale and mesoscale are basically the same,the main cycle of 24 ~ 32 A,secondary cycle of 6 ~ 10 A,small time scale period is slightly different,Guanzhong has been 3 ~ 5 A and the cycle,only in 1980 s there have been 2 ~ 3 a period;Northern Shaanxi main change cycle is relatively weak,26 ~ 30 A,secondary cycle of 15 ~ 18 A,in recent years,the extreme precipitation events are at increased partition period;fourthly the main mode of extreme precipitation in flood season is one reverse phase change in Northern Shaanxi Province and other parts of the province,the secondary mode is north and South sector in Qinling Mountains as the reverse phase change,the third mode is a reverse phase change of Guanzhong and southern Shaanxi,northern shaanxi.(4)Xi'an strong precipitation time mainly in mid July to mid August,early August is the most obvious diurnal variation,nocturnal characteristics,southeast direction for the precipitation of high incidence area,Lantian;weather situation mainly includes 5 types: the Western Pacific subtropical high pressure(Subhigh)control (V)northwest airflow type(W-N),low trough type(V),the influence of typhoon remote(T),the edge of the subtropical high effect(S),the subtropical high and Northwest Airflow Type influence,followed by the low trough type;the use of adjacent observations sounding nearly 12 h in the potential the establishment of forecast equation,case analysis to determine the forecast index y = 200 can be used as a reference potential forecast of short duration heavy rainfall,when the forecast index was 500 ~ 3500,200 ~ 500,the precipitation process,local short term Pro The indication effect of near strong precipitation is better.