陕西省榆林地区1644-1949年旱灾与干旱气候事件

目的]揭示榆林地区1644—1949年干旱灾害等级、时间变化及成因。方法]根据历史文献统计分析,并应用小波分析等方法。结果]在1644—1949年的306a里,榆林地区有明确记载的旱灾86次,平均每3.6a发生1次。其中轻度旱灾发生32次,中度旱灾发生41次,大旱灾发生7次,特大旱灾发生6次,分别占旱灾总数的37.2%,47.7%,8.1%和7.0%。榆林地区1644—1949年旱灾变化可分为2个阶段,第Ⅰ阶段为1644—1829年,为旱灾少发阶段;第Ⅱ阶段为1830—1949年,为旱灾多发阶段。该区1876—1879年、1899—1901年和1928—1931年连年发生严重旱灾,代表了3次干旱气候事件的存在,在此期间,榆林地区的气候性质发生了改变,由温带半干旱大陆性季风气候转变为温带干旱非季风气候。榆林地区1644—1949年的旱灾有7a左右的短周期,14a左右的中周期,36a左右的长周期。结论]榆林地区旱灾发生的根本原因是当年降水量的减少,大旱灾和特大旱灾发生年的降水量分别减少100mm余和150mm余,中小规模的旱灾部分是降水量集中造成,部分是年降水量减少造成的。旱灾等级与频次指示,1644—1829年为气候较湿润阶段,1830—1949年为气候较干旱阶段。

Drought Disaster and Drought Events in Yulin Area of Shaanxi Province from 1644 to 1949

Objective] To reveal the level, temporal change and reason of drought disasters in Yulin area of Shaanxi Province during the period of 1644-1949.Methods] Compilation of historical data and wavelet analysis method were used to research relevant problem.Results] During the 306 years from 1644 to 1949, the drought disasters clearly recorded were 86 times, with average once every 3.6 years. The drought disaster happened 32, 41, 7 and 6 times for mild, middle, great and serious levels, respectively. The distribution of drought disasters in Yulin area during the period of 1644-1949 could be divided into two stages:from 1644 to 1829 with low drought frequency, from 1830 to 1949 with high drought frequency. The continuous drought disasters from 1876 to 1879, 1899 to 1901 and 1928 to 1931 were particularly serious, representing the arid climate event. According to wavelets analysis, it was known that there were mainly 7-year period, 14-year period and 36-year period for drought in Yulin area.Conclusion] Most of the drought were caused by decreasing of precipitation. In general, precipitation decreased more than 100 mm and 150 mm in the years of great and serious drought, separately. Precipitation that distributed non-uniformly and changed greatly in different years was the main cause of mild and middle drought disasters. Grades and times of drought disasters indicates that climate was more humid during 1644 to 1829 than that during 1830-1949.