洞庭湖流域旱涝异常的时空分布及其与大气环流和水汽输送的关系

Spatial-temporal Distribution Characteristics of Droughts/Floods Abnormality in the Dongting Lake Basin and Its Relationship with Atmospheric Circulation and Water Vapor Transport

利用洞庭湖流域1960~2017年103个气象站点逐月降水数据和NCEP/NCAR再分析数据,通过计算Z指数和区域旱涝指数,对流域近57年来季节性旱涝异常的时空变化和典型旱涝年份的同期大气环流、水汽输送形势进行分析,以加强对季节性旱涝异常及可能的直接影响因素的认识。结果表明:洞庭湖流域连续两年出现旱涝异常的可能性不大,春、夏季节发生旱涝异常的一致性较秋、冬季小。在春、秋季节,流域干湿变化表现出年际性并有明显的空间分布,在冬、夏季节表现出年代际转换并存在变湿的趋势。此外,各季节均表现出涝重于旱的统计特征。同期大气环流形势会对流域旱涝异常产生显著影响,当西风带经(纬)向环流偏强时,干旱易出现在冬(夏)、春(秋)季节。当副高脊线偏北时,干旱易出现在夏、秋季节;在冬季时,偏强偏西的副高易使流域出现冬涝。流域Z指数在各季节均与净经向水汽通量呈显著正相关,在春、夏、秋季节与净水汽收支呈显著正相关,而在冬季可能与降水动力条件关系更密切。

Based on the monthly precipitation data of 103 meteorological stations in the Dongting Lake Basin from 1960 to 2017 and NCEP/NCAR reanalysis data, combining the Z-index and the droughts-floods region index, in order to enhance the understanding of seasonal droughts-floods abnormality and possible direct influence factors, the spatial-temporal distribution characteristics of seasonal droughts-floods abnormality, the synchronic atmospheric circulation and water vapor transport feature in typical droughts-floods years in the basin over 57 years were analysed. The results showed that in the statistical sense, it was unlikely that the droughts/floods abnormality appeared for two consecutive years, and the frequency of coexistence of droughts-floods abnormality in spring and summer was higher than that in autumn and winter in the basin. The dry and wet evolution showed interannual characteristic and obvious spatial distribution in spring and autumn, showing interdecadal transition and wetting tendency in winter and summer. In addition, each season showed that flood was heavier than drought in statistical sense. The synchronic atmospheric circulation feature would exert significant impacts on the droughts-floods abnormality in the basin. When the meridional(zonal) circulation was strong, the droughts were more likely to occur in winter(summer) and spring(autumn). When the subtropical high ridge was northward, the droughts tended to occur in summer and autumn;when the subtropical high was strong and westward, the floods were more likely to occur in winter. The Z-index was significantly positively correlated with the net meridional water vapor flux in each season, and the net water vapor budget in spring, summer and autumn, and may be more closely correlated with precipitation dynamic condition in winter.