Characteristics Of Local And Regional Persistent Heavy Rain Events In The Eastern Monsoon Region Of China

Persistent heavy precipitation events(PHPEs),a kind of high-impact extreme weather events,with high intensity,large impact area and long duration,often cause tremendous impacts on society and ecosystems.Using a daily precipitation dataset of 470 climate stations over the monsoon region in eastern China,first of all,according to the duration and intensity of heavy precipitation to identify the PHPEs and analyzes their characteristics with the different duration.Based on the knowledge of the PHPEs,the PHPEs that cause severe floods are often affected by large-scale circulation,a dynamic process,and have the influence area.We developed an automated technique to identify RHPEs with impact area,duration and intensity,then,explore their temporal and spatial characteristics.The main findings and conclusions are as follows:(1)The characteristics of PHPEs with the different duration are investigated.Total of 64,487 PHPEs are identified,then classified into three levels based on different duration: 1 day(58904),2 days(4884),3 days and above(699)events,and mainly in the short duration of the PHPEs.The PHPEs show significant spatial and seasonal differentiation.Spatially,the PHPEs occurred mainly in the tropical and subtropical monsoon regions,especially south of the Yangtze River and South China as high incidence areas with the high frequency,and show the significant cluster,especially lasting 3 days and above.In the temperate monsoon region,there is only a few long duration of the PHPEs around the Bohai area.In addition,the spatial distribution of the intensity of the PHPEs is similar to the frequency,which means that the longer duration of the PHPEs,the stronger intensity,the more concentrated in space.Seasonally,the PHPEs mainly concentrate in the spring and summer,1 to 2 days of PHPEs are mainly in the spring;in the summer,the tropical subtropical monsoon region is mainly for 3 days and above.In addition,the peak of the monthly frequency of lasting 3 days and above is earlier than 1 to 2 days,appearing in June.(2)Trends of PHPEs with the different duration are examined.The duration and intensity of the PHPEs are increasing,and the increase of the duration is more obvious.From a spatial perspective,the PHPEs are significant regional differences.In the tropical and subtropical monsoon zones,the PHPEs with the different duration are increasing during 1960-2013,spatial distribution of the PHPEs lasting 2 days and above are similar to 1 day,but less irregular,the South of the Yangtze River and southern China show a rising trend,6% /10a;the temperate monsoon zone with a downward trend,only maximum daily precipitation increase with a trend of 0.12% /10 a.In general,the interdecadal changes of the PHPEs display a typical ?W-shape? structural characteristic,and have been increasing since the late 1970 s and the early 1990 s.(3)The characteristics of RHPEs with the different grades are analyzed.In total,2608 RHPEs are identified over the period 1960-2013.All events are classified into three categories: Grade 1(652),Grade 2(652)and Grade 3(1304)events,from least to most severe RHPEs,based on an integrated index which been built by D,Sgrid,Pgrid and VPgrid.Frequency,the RHPEs also dominated by short duration;Spatially,the RHPEs are similar to the PHPEs,mainly located in the the tropical and subtropical monsoon zones,particularly the most severe ones(Grade 1),are mainly located in the middle and lower Yangtze River basin(MLYRB)and southeastern China.RHPEs that occur in the temperate monsoon zone are mainly Grade 2 and Grade 3 ones.Seasonally,the RHPEs mainly occur from May to August,and the peak frequency appears in July.In addition,the variation pattern of monthly spatial distribution is consistent with the movement pattern of the monsoon belt(4)Trends of RHPEs with the different grades are revealed.In general,Trend analysis shows that frequency and integrated intensity of all RHPEs have increased during 1960-2013 for eastern China.This means RHPEs are becoming more severe and frequent.However,temporal trends vary for events of different grades: the Grade 1 and Grade 2 events are increasing,while the Grade 3 events are decreasing.Distinctive regional patterns also exist.The events become more frequent and severe in the tropical and subtropical monsoon zones,where most of the increase could be attributed to the increase in the Grade 1 events.The temperate monsoon zone experiences no significant change in the RHPEs frequency,but a decrease in their integrated intensity,especially that of Grade 1 events.The interdecadal changes of the RHPEs show a sudden change in 1987,from the 1960 s to mid-1980 s,there was a significant downward trend,with a significant upward trend in the late 1980 s.Therefore,the trends of the Sgrid,Pgrid and VPgrid of RHPEs with different durations during the two periods of 1960-1986 and 1987-2013 are analyzed.The results show the multiday events are becoming more severe due to the increase in the impact area,precipitation depth and total precipitation volume,whereas little change has occurred with single-day events.Moreover,more increase is found for more severe events,i.e.multiday events with longer return period.The observed increase in severity of Grade 1 and multiday RHPEs may significantly increase the risk of flooding over eastern China.