基于梅雨监测指标的安徽江淮地区梅雨过程识别

Meiyu identification of Yangtze-Huaihe region in Anhui province based on Meiyu monitoring indices

据国标《梅雨监测指标》规定的入梅和出梅条件,识别了安徽省江淮地区1957—2020的梅雨过程及其特征量,对比分析了国标与其发布前其他研究在雨日、出梅条件等方面的异同及其对梅雨过程识别和特征量的影响。结果表明:据国标识别的安徽江淮地区梅雨过程和特征量与其他现有研究方法的识别结果基本一致,以日降水量大于气候平均6—7月日降水量的1/2为雨日,比据国标规定的雨日识别的空梅年增多,识别的部分年份入梅偏晚;1957—2020年中有13个空梅年,约占1/5,非空梅年平均于6月19日入梅,7月13日出梅,梅雨期长23.7 d,梅雨期和降水集中期的降水量分别为270.7和263.0 mm,约占年降水量的1/4,占6—7月降水量的3/4;当研究区域较小时,应据环流和雨日条件确定区域的出梅日,不宜以最后一个雨期结束日的次日为出梅日;安徽江淮地区在空、枯梅容易出现较重旱情,尤其是连续的空、枯梅年,而梅雨量大且集中的年份易发生洪涝,尤其是梅雨量大于400 mm的年份(如2020年)。

According to the definition of the onset and the ending of the Meiyu period in China’s national standard“Meiyu Monitoring Indices”(GB/T 33671—2017),Meiyu processes and their signatures in the Yangtze-Huaihe region of Anhui province during 1957—2020 were identified.The identified signatures of the Meiyu process were compared with those identified by methods proposed before the release of the national standard to investigate the impact of the Meiyu identification method on its signatures.The results show an overall consistency between the Meiyu processes identified based on the national standard and other methods.The identified Meiyu processes based on rain day(which is defined as the days with the precipitation greater than half of the average daily precipitation during June-July)have generally more years with no Meiyu and later onset of Meiyu than those identified based on the national standard.A total of 13 empty Meiyu seasons are identified during 1957—2020,which results in an empty Meiyu frequency of about 20%.For the years with Meiyu,their average onset and ending dates are 19 June and 13 July respectively,which results in an average length of Meiyu season of 23.7 days.The average amount of precipitation-concentration period and the whole period of Meiyu season are 270.7 and 263.0 mm respectively,accounting for about 1/4 of annual precipitation and 3/4 of precipitation during June-July.When the study area is small,instead of the day after the last rainy day,the ending date of a Meiyu season should be determined based on the conditions of atmospheric circulation and regional rain days.It is also shown that there are severe droughts in the Yangtze-Huaihe region of Anhui province,which are more likely to appear during empty or dry Meiyu seasons,especially when there are consecutive empty or dry Meiyu seasons.Conversely,in the same region,severe floods are more likely to appear in years with heavy and concentrated precipitation during the Meiyu season,especially for those with precipitation larger than 400 mm in Meiyu season,e.g.the year 2020.