基于SPEI的黄淮地区夏季干旱时空异常特征及成因

Spatial and Temporal Characteristics of Summer Drought Anomaly and Its Causes Based on SPEI in Huang-Huai Area

选取黄淮流域及周边地区147个气象站1962—2015年逐月气温、降水观测资料,利用标准化降水蒸散指数(standardized precipitation evapotranspiration index,SPEI)分析了该地区近54 a夏季干旱变化及其异常成因。结果表明:黄淮地区近54 a夏季呈稳定略偏旱趋势,1990年代起该地区夏季经历了先湿后干的演变。EOF(经验正交函数)分析表明黄淮地区夏季SPEI的前3个模态为一致旱涝型、南北反位相型和东北-西南反位相型。该地区夏季偏旱年份为Ⅰ类或Ⅲ类雨型且夏季各月干旱成因有所不同,其中6月亚洲区极涡强度偏弱时,同期黄淮地区降水偏少,干旱频发;7月西太平洋副热带高压(副高)西伸脊点位置偏东(位于129°E以东),黄淮地区发生干旱的可能性较大;8月副高强度越弱,干旱风险越大。夏季青藏高原地面加热场强度偏强时,中高纬冷空气势力较弱难以影响到黄淮地区,同时,副高位置异常偏北偏西,导致该地区偏旱。

Based on the monthly temperature and precipitation observation data from 147 meteorological stations during 1962-2015 in the Huang-Huai River Basin and surrounding area. The standardized precipitation evapotranspiration index（ SPEI） was used to analyze the summer drought change and its abnormal cause. The results show that the Huang-Huai area has maintained a stable and slightly drought trend in summer in recent 54 a. In the 1990 s,the area experienced the evolution of the first wet and then dry. The first three EOF（ empirical orthogonal function） modes of SPEI in summer in the Huang-Huai area showed consistent variation,the north-south anti-phase variation and northeast-southwest anti-phase variation,respectively. Discussion on the causes of drought in summer indicated that compared with flood years,it occurred either type I or type III rain in drought years. From June to August,the causes of drought in the Huang-Huai area were intra-seasonal differences. Using composite analysis method to discuss the characteristics of atmospheric circulation under the spatial distribution pattern of drought anomaly in the Huang-Huai area,when the intensity of the polar vortex in Asia was relatively weak in June,the precipitation in the Huang-Huai area was less and the drought was more frequent. The position variation of the western Pacific subtropical high（ WPSH） in July had an important impact on drought and flood in the Huang-Huai area. The westward ridge point of the WPSH extended eastward,which was located east of 129°E,the possibility of drought in the Huang-Huai area was greater in July. When the intensity of WPSH was weak in August,the risk of drought in the Huang-Huai area increased. When the intensity of the surface heat field on the Tibetan Plateau was stronger in summer,cold air from the mid-latitude was weak,and it was difficult to affect the Huang-Huai area. At the same time,the position of WPSH was abnormally northward and westward,which resulted in drought in the area.