退耕还林工程实施以来延安市降水变化特征分析

Since the Implementation of the Project to Return Farmland to Forest(2000),the Characteristics of Precipitation Changes in Yan'an City has been Analyzed

利用延安市2001-2020年13个国家地面气象观测站的降水观测资料,分析退耕还林工程(2000年)实施以来,延安市近20a降水量的年、月降水量和降水日数变化特征,为延安市水资源的合理开发利用及防汛抗旱工作提供技术支撑。结果表明:近20a来延安地区的降水量变化明显,主要表现为:年平均降水量总体呈增多趋势,增加幅度为2.1mm/a;地域分布上南部县区多于北部县区,总体偏多13%;全年降水主要集中在汛期(5-9月),约占全年平均降水量的80%,以7月最为突出,占23%。各县区全年7、8月月平均降水量增多明显,9月减少明显。3、12月略有下降。2001-2020年延安年平均降水日数为86天,最多为105天,出现在2003年,最少为72天,出现在2005年。近20a来,延安以小雨(阵雨)出现的次数最多,占总降水次数的73.5%,大暴雨最少,不足总降水次数的0.1%。暴雨在每年5-10月均有出现。大暴雨主要集中在6-8月份。小雨(阵雨)以9月份出现的频率最高,中雨到大暴雨均以七月份发生的频率最高。近20a来,延安各级降水日数总体以1.0d/a的趋势在增加。其中,小雨日数略微减少,减少幅度为0.3d/a,中雨日数、大雨日数、暴雨日数均分别以1.0d/a、0.3d/a、0.1d/a的线性趋势在增加,大暴雨日数基本无变化。

Using the precipitation observation data of 13 national ground meteorological observation stations in 2001-2020,we analyze the characteristics of annual and monthly precipitation and precipitation daily changes in nearly 20 a of the project(2000)to provide technical support for the rational development and utilization of water resources in Yan'an City and flood control and drought relief work.The results show that the precipitation in Yan'an in nearly 20a,mainly showing the overall annual average precipitation of 2.1mm/a.Generally,the southern counties are more than the northern counties,and 13%;the annual precipitation is mainly concentrated in flood season(May-September),accounting for about 80%of the annual average precipitation in July and 23%.The average monthly precipitation of all counties and districts increased significantly in July and August,and decreased significantly in September.March and December.The average annual precipitation days in Yan'an from 2001-2020 were 86 days,at most 105 days,appearing in 2003,at least 72 days,and appearing in 2005.In the past 20a,Yan'an has seen the most light rain(showers),accounting for 73.5%of the total precipitation number,and the least heavy rain,less than 0.1%of the total precipitation number.Heavy rains occur in May to October every year.Heavy rain is mainly concentrated in June-August.Light rain(showers)with the highest frequency in September,moderate rain to heavy rain are the highest frequency in July.For nearly 20a,the number of precipitation days at all levels in Yan'an is generally increasing by 1.0d/a.Among them,the number of light rain days decreased slightly,with a reduction range of 0.3d/a.The number of moderate rain days,the number of heavy rain days and the number of rainstorm days all increased with the linear trend of 1.0d/a,0.3d/a,0.1d/a,respectively,and the number of heavy rain days was basically unchanged.