中国南北过渡带短周期旱涝急转及潜在驱动因素分析

Analysis on spatio-temporal evolution characteristics of short-cycle drought-flood sudden alteration and potential driving factors in the north-south transitional zone of China

本文根据中国南北过渡带32个气象站1960-2018年逐月降水资料,计算短周期旱涝急转指数(short-cycle drought and flood sudden alteration index,SDFAI),采用M-K趋势分析法、R/S分析法、M-K突变检验、滑动T检验研究了该区域5~9月内短周期旱涝急转时空演变特征;分析了典型旱转涝与涝转旱时期大尺度大气环流特征;采用交叉小波变换对SDFAI潜在驱动因素进行了探讨。结果表明:(1)5~6月、6~7月、7~8月、8~9月内旱涝急转均以涝转旱为主,且5~6月和6~7月为旱转涝和涝转旱多发时期;另外各时段年代际旱转涝与涝转旱事件趋势在1990 s出现明显转折,整体呈现“V型”和“倒V型”变化特征。(2)旱涝急转事件在岷江一带、陕南周边地区较为多发;各时段内区域Hurst指数均值分别为0.62、0.62、0.61、0.68,表明过渡带内SDFAI的变化趋势仍会持续至未来一段时期。(3)在典型旱涝急转时期,西太平洋副热带高压与南亚高压涝期“西伸东进,相向而行”,旱期“东退西进,相背而离”,水汽输送条件整体呈现出相反的变化特征。(4)在北极涛动指数(AO)、NINO 3.4区域海温指数(NINO 3.4)、太阳黑子指数(TSNI)、太平洋年代际涛动指数(PDO)4项指数中,TSNI对SDFAI变化的影响最强,主要表现为TSNI超前1/4周期;NINO 3.4和PDO次之,对SDFAI以正向驱动为主;AO对SDFAI变化的影响最小。

Based on the monthly precipitation data of 32 meteorological stations from 1960 to 2018 in the northsouth transitional zone of China,the short-cycle drought and flood sudden alteration index(SDFAI)was calculated in May-September,and the spatio-temporal evolution of short-cycle drought and flood sudden alteration(SDFSA)was investigated by using Mann-Kendall trend analysis,R/S analysis,Mann-Kendall test,and Moving t test. Then the characteristics of large-scale atmospheric circulation during typical drought-to-flood and flood-to-drought periods were analyzed. Finally,the potential driving factors of SDFAI were revealed by applying cross wavelet transform. Results showed that:(1)During May-June,June-July,July-August and August-September,flood-to-drought events were more pronounced,and SDFSA events were more frequent in May-June and June-July. In addition,the trend of interdecadal SDFSA events showed a significant turning point in the 1990s,presenting the "V-shaped" and "inverted V-shaped" change modes.(2)Spatially,SDFSA events were more frequent in the Min River and the surrounding areas of southern Shaanxi province. The mean values of regional Hurst in each period were 0.62,0.62,0.61 and 0.68,respectively,indicating that the changing trend of SDFAI will continue for some time.(3)During the flood period of typical SDFSA,the Western Pacific Subtropical High(WPSH)extended westward and the South Asia High(SAH)advanced eastward,approaching each other. While during the drought period,WPSH retreated eastward and SAH advanced westward,moving away from each other. Moreover,the water vapor flux conditions held the relatively opposed characteristics.(4)TSNI had the strongest impact on the SDFAI,mainly leading SDFAI by 1/4 cycle. Followed by NINO 3.4 and PDO,both of which had positive driving force on the SDFAI. AO had a relatively weak effect on the SDFAI as a whole.