淮河流域春夏季降水位相变化特征

淮河流域的降水异常容易导致旱涝灾害。本研究从降水位相变化的角度,对淮河流域春夏季降水规律作了分析。在近50 a中,春夏季降水持续偏多的典型事件发生频次较多,强度较大。1960年代初期—1970年代末期和2000年代的两个时期内发生降水位相变化的站次都呈现减少趋势,而在近几年则显著增加。通过S-EOF分解,第1模态代表春、夏季降水持续同位相变化,其时间系数在近年来持续上升;第2模态为春夏季降水反位相变化特征,此模态的时间系数有明显的年代际变化特征。进一步研究发现:前冬和春季,当赤道太平洋持续发生El Ni1o事件,南印度洋偶极子负位相;春季东亚副热带急流偏弱,春夏季中国东部850 hPa均存在南风异常,有利于淮河流域春夏季降水持续正位相变化;持续负位相年则反之。当春季东亚副热带急流偏强(弱),夏季位置偏南(北);中国东部沿海春季海温偏低(高);春夏季间中国东南部850 hPa经向风由北(南)风异常转变为南(北)风异常,可能会导致春季降水负(正)位相—夏季正(负)位相的变化。

Anomalous spring and summer precipitation changes in the Huaihe River Basin

Huaihe River is one of the main rivers in China.It lies between the Yellow River and Yangtze River.Since ancient times,floods and droughts occurred frequently in Huaihe River Basin with significant casualties and economic losses.In developing measures for disaster prevention or emergency response for disaster relief,the study of floods and droughts caused by precipitation anomaly in Huaihe River Basin should be strengthened.Based on the observation dataset,this study not only defines the precipitation transition events from spring to summer,but also produces its intensity using total seasonal precipitation.The precipitation transition from spring to summer is analyzed by using the 30 gauge stations in Huaihe River Basin during 1961-2014.The typical patterns of Wet-Wet and Dry-Wet transitions generally occurred and their intensities were stronger in the past 54 years.The results indicate that temporal variation of transition event shows interannual and interdecadal variabilities.The significant decrease trend of transition frequency is detected during 1961-1979 and 2000-2010,but it has increased in recent years.The transitions often occur in more than one-third stations over half sample periods.This study applies the Season-reliant Empirical Orthogonal Function(S-EOF) analysis to detect major modes of seasonal precipitation.Based on S-EOF method,the cumulative variance contribution of the first mode is up to 34.4%.The principal component 1(PC1) illustrates the continuous positive precipitation anomaly in spring and summer in most areas,and it is worthy to notice the rising of its time coefficient in past few years.Otherwise,transition from negative to positive precipitation anomaly and interdecadal variation of time coefficient are shown by PC2.Furthermore,results show that PC1 relates to continuous El Niño event from early winter to spring,positive East Asian subtropical westerly anomaly at 200 hPa in spring,positive Indian Ocean Dipole and south wind anomaly at 850 hPa over eastern China from spring to summer.The reverse occurs during a continuous negative phase scenario.The negative SSTA in eastern coast of China,the significant changes of northward East Asian subtropical westerly,and the shift of meridional wind anomaly at 850 hPa over southeastern China cross seasons play important roles in the occurrence of PC2 in Huaihe River.