121年梅雨演变中的近期强年代际变化

Recent strong decadal change of Meiyu in 121 years

  • 摘要: 1885年以来长江中下游梅雨期在70年代末发生了一次强年代际突变:从1958-1978年的弱梅雨时段突变为1979-1999年的强梅雨时段.后21年梅雨量比前21年平均增加了66%,长江中下游夏涝年出现率显著增长.此两时段梅雨由弱转强和出梅/入夏期由偏早转为延迟呈密切联系,这在相当程度上反映中国东部夏季气候-水资源分布的突变.进一步分析,发现两时段内影响梅雨盈亏年际变化的前期因子也很不同.研究了两时段梅雨盛行趋势突变的成因,发现与显著增强的人类活动有关:20世纪70年代末,我国工业开始大发展,大气污染的增长导致地面太阳辐射减少,中国北方沙化土地面积又迅速扩大.同时温室效应的增长也表现在我国暖冬(尤其是2月).此外,长江中下游1月降水量增多;厄尔尼诺事件从20世纪70年代末开始也明显增多.由上述5因子组成的相关点聚图凸显出前后两时段处于截然不同的地-气环境位相.从2000年开始,长江中下游梅雨又进入新的偏少期,中国东部夏季水资源分布正面临新的变化.

     

    Abstract: A strong decadal change of the Meiyu periods in the mid-lower Yangtze basin occurred in late 1970s since 1885:a weak Meiyu stage in 1959-1978 abruptly transformed into the strong one during 1979-1999.The average Meiyu amounts of later 21 years increased by 66% compared with the former years,accompanied with a significant increase of the occurrence of the summer waterlogging in the mid-lower Yangtze basin.The change of Meiyu periods is closely related with the frequently postponed phenomena of their ending dates and the later onsets of high summers in the mid-lower Yangtze.In a considerable degree,it reflects an abrupt change of the summer climate in eastern China.Through analysis,it is found that the preceding factors effecting the inter-annual changes of Meiyu in above 2 stages are also very different from each other.The causes of such decadal change are associated with following strengthening anthropogenic activities:China's industrialization has greatly accelerated since 1970s,accompanied with the increase of the atmospheric pollution and the reduction of the solar radiation on the ground,the sand area of northern China also expands fastly by overgrazing,and the enhanced greenhouse effect is significantly manifested in winter warming(especially in February).Meanwhile,the January precipitation of the mid-lower Yangtze tends to increase,and the El-nino events have occurred more frequently since late 1970s.The correlation-scattered diagram formed by above 5 factors clearly shows that the 2 stages with opposite anomalies of Meiyu period are grouped with the 2 totally locations and very different environmental(land-atmosphere) conditions.Now we have very possibly faced again a new stage of lesser Meiyu starting in 2000.

     

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