东亚夏季风北部边缘区近260年以来的极端干旱事件

EXTREME DROUGHT EVENTS OVER THE PAST 260 YEARS IN THE NORTHERN FRINGE OF EAST ASIAN SUMMER MONSOON

基于高分辨率的树轮年表数据集,分析了近260年东亚夏季风北部边缘区发生的极端干旱事件,并利用统计算法分析了极端干旱事件的强度及影响范围.结果显示,区域在1890～ 1894年、1898～ 1905年、1926～ 1932年及1991～1997年发生极端干旱事件,其中1890～1894年的极端干旱事件在部分年表中表现显著,1898～ 1905年的极端干旱事件在大部分年表中均有所记录,1926～ 1932年的极端干旱事件几乎在所有年表中均有记录,是近260年来发生的强度最强、波及范围最广的干旱事件,1991～1997年的极端干旱事件影响范围不大,但在其影响区域强度较高.

The northern fringe of East Asian summer monsoon （EASM） includes the west side of Great Khingan Range, southeastern of Inner Mongolia Autonomous Region, northern of Hebei and Shanxi Provinces and the Ordos Plateau. During historical periods, fluctuations in the intensity of EASM have caused multiple drought and flood events in this region. By employing the database of 9 high resolution tree-ring width chronologies and the Palmer Drought Severity Index （PDSI） grid data neared the locations of chronologies, the present study aims to analyze the extreme drought events from 1740 A.D. to 1999 A.D. in the northern fringe of EASM. By means of statistical methods, we also calculated the fractions of the chronologies exceeding each of critical values （including mean value （i.e., 0）, 1 time standard deviation departure to the mean value （i. e., ± 1SD）, and 2 times standard deviation departure to the mean value （i. e., ±2SD） ） which indicate the fractions of those chronologies with extreme drought events recorded, and analyzed the intensity and affected areas of each extreme drought event. The areal mean tree-ring series show that over the past 260 years the northern fringe of EASM has experienced multiple drought events, which include the periods from 1890 A.D. to 1894 A.D., 1898 A.D. to 1905 A.D., 1926 A.D to 1932 A.D., and 1991 A.D. to 1997 A.D. In addition, the statistics results show that over the past 260 years there were variations in the temporal and spatial trends of each extreme drought events： the extreme drought event occurred from 1890 A.D. to 1894 A.D. was recorded in some chronologies with significant low values （i.e., 〈-1） , but it was not recorded by the other chronologies, indicating that although the areal mean series did depict this drought event, its influences were limited within some areas; the extreme drought event occurred from 1898 A.D. to 1905 A.D. had been recorded by most of available tree-ring chronologies （over 70% of the available chronologies）, suggesting it influenced most of the study area; the extreme drought event occurred from 1926 A.D. to 1932 A.D., which was marked by nearly all of the chronologies （over 90% of the available chronologies） with abnormal low values, was an exceptional and the most intensive and extensive climate disasters over the past 260 years in this region; the drought event occurred from 1991 A.D. to 1997 A.D. was recorded by 60% of the available chronologies, and beyond 50% of these recorded chronologies showed abnormal low values （i.e., 〈-1 ）, which demonstrates that although this drought event spread a limited areas, its affected areas was dominated by extreme dryness.