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通过对榆林地区文献资料的搜集整理,运用统计方法和小波变换,研究了该地区明代旱灾的等级、频次、周期和气候特征。结果表明,榆林地区明代共发生旱灾70年次,平均0.25次/a,且以大旱灾为主,夏季是旱灾多发季节。旱灾的发生具有明显的阶段性,1375-1424年、1555-1584年、1590-1614年是3个旱灾少发阶段,1480-1504年、1520-1539年、1625-1644年是3个旱灾多发阶段。榆林地区明代旱灾的准周期是3 a,8 a,17 a,39 a。各等级旱灾准周期相近,短周期约为3～4a,大旱灾的第一主周期为39 a。提出了榆林地区明代存在6个干旱气候事件,干旱气候事件期间,该区由半干旱气候变为干旱气候;大旱灾发生年的年降水量为320 mm左右,中度旱灾年的年降水量380 mm左右。
Through collecting and sorting the literature data of Yulin area, the paper uses the statistical method and wavelet transform to study the grade, frequency, period and climatic characteristics of drought in the Ming Dynasty. The results showed that in the Yulin area, a total of 70 times of drought occurred in the Ming Dynasty with an average of 0.25 times per year, with a severe drought as the main season and a summer drought season. The occurrence of drought has obvious stages. The periods of 1375-1424, 1555-1584 and 1590-1614 are three less developed stages of drought. In the period of 1480-1504, 1520-1539 and 1625-1644, there are three frequent occurrences of drought stage. The quasi-period of drought in Ming Dynasty in Yulin was 3 a, 8 a, 17 a, 39 a. The quasi-periods of drought at all levels are similar, the short period is about 3 ~ 4a, and the first main period of drought is 39 years. It is proposed that there are 6 arid climate events in Yulin area during the Ming dynasty. During the arid climate event, the area changed from semi-arid climate to arid climate. The annual precipitation during the severe drought year was about 320 mm, and the annual precipitation during moderate drought year 380 mm or so.