我国旱涝气候灾害的年代际变化及其与东亚气候系统变化的关系

Interdecaldal Variations of Drought and Flooding Disasters in China and Their Association with the East Asian Climate System

通过观测资料分析我国旱涝灾害的年代际变化特征,表明从1976年之后迄今我国华北地区发生持续干旱,严重影响了此地区的水资源和经济的可持续发展,并且长江、淮河流域夏季季风降水明显增加,洪涝灾害频繁发生。作者还从东亚气候系统的年代际变化系统地分析了发生在我国旱涝气候灾害年代际变化的机理。分析结果表明:从20世纪70年代中后期迄今,热带中、东太平洋海温上升,并出现“类似于厄尔尼诺(El Ni^no)型”分布的年代际海温距平。这不仅引起了东亚和西太平洋上空EAP型遥相关环流异常分布的年代际变化,使得从1976年之后迄今东亚夏季风变弱、西太平洋副热带高压偏南、偏西,而且引起了热带Walker环流的变化;并且,由于热带Walker环流的年代际变化,引起了从20世纪70年代中后期到现在北非上空下沉气流的加强,从而使得萨赫勒及以东地区上空反气旋环流异常增强,并由于遥相关波列的传播,从而导致我国华南上空反气旋环流距平的增强;此外,中高纬度欧亚型遥相关环流异常分布也发生了年代际变化,使得1976年之后我国华北地区上空出现反气旋环流异常。这些使得到达华北的偏南季风气流减弱和长江、淮河流域水汽输送的辐合,从而导致了我国旱涝的年代际变化。分析结果还表明了从20世纪70年代后期迄今青藏高原冬、春积雪天数增多,深度加深,以及我国西北干旱、半干旱区地气温差增大,这些有利于长江和淮河流域夏季降水增多,而不利于华北地区夏季降水。

The characteristics of the interdecadal variations of drought and flooding disasters in China are analyzed by using the observed data. The results show that the persistent droughts occurred in North China from 1976 to now, which seriously affected water resources and sustainable development of economy in this region. And the summer monsoon rainfall obviously increased and flooding disasters frequently occurred in the Yangtze River valley and the Huaihe River valley in this period. Moreover, the physical mechanism of the interdecadal variations of drought and flooding disasters occurring in China is analyzed from the interdecadal variability of the East Asian climate system. The analyzed results show that the SST increased and an interdecadal SST anomaly pattern which is similar to El Nin^～o appeared in the tropical central and eastern Pacific from the late 1970s to now. This has caused not only the interdecadal variation of circulation anomaly distributions of the East Asia- Pacific （EAP） pattern teleconnection over East Asia and the the western Pacific, which has led to the weakening of the East Asian summer monsoon and the southward and westward shifts of the western Pacific subtropical high, but also the interdecaldal variability of the Walker circulation over the tropics after 1976. And the results also show that the interdecadal variability of the Walker circulation from the late 1970s to now caused the intensification of descending flow in North Africa, which led to the intensification of the anticyclonic anomaly circulation in the Sahelian region and east of North Africa. And due to the propagation of quasi-stationary planetary waves, the intensification of anticyclonic anomaly circulation over the Sahelian region caused the appearance of an anticyclonic anomaly circulation over South China from the late 1970s. Besides, since an interdecadal variation for the circulation anomaly distributions of the Eurasian （EU） pattern teleconnection over middle and high latitudes also occurred in the late 1970s, an anticyclonic circulation anomaly distribution over North China was caused after 1976. These led to the weakening of the southerly monsoon flow reaching North China and the convergence of water vapor transport in the Yangtze River valley and the Huaihe River valley, thus, the interdecadal variation of droughts and floods was caused in China in the late 1970s. The analyzed results also indicate that the days and thickness of winter and spring snow cover in the Tibetan Plateau increased, and the difference between the ground surface temperature and surface air-temperature in spring in the arid and semi arid ar eas of Northwest China became large from the late 1970s. These are helpful to the increase of summer monsoon rainfall in the Yangtze River valley and the Huaihe River valley and the decrease of summer rainfall in North China.