黄河下游历史泥沙灾害的宏观特征及其与流域因素及人类活动的关系(Ⅰ)──历史气候及植被因素的影响

Historical sediment-related disasters in the lower Yellow River in relation with drainage basin factors (Ⅰ): influence of climate and vegetation

以历史上黄河下游的决溢频率为泥沙灾害的代用指标；研究了黄河下游历史泥沙灾害的宏观特征．研 究表明，气候因素对黄河下游决溢频率有深远的影响．隋唐以前，天然植被尚未遭到显著破坏，当湿润指标 增大时，有利于植被的生长，故黄河下游决溢频率减小．１０世纪以后，二者的关系与此相反，当湿润指标增 大时，决溢频率也增大，反之亦然．每世纪大旱年颁次与每世纪决溢频次之间呈明显正相关，说明目前受到 各方面广泛关注的黄河下游“小水大灾”现象，在历史上已经存在．干旱时期中，河槽萎缩，一旦大水来 临，很容易发生决溢．以华山松树木年轮指数为气温的代用指标，研究了气温变化与决溢频率变化的关系， 结果表明，在５０ａ的尺度上，当气温降低时，决溢频率增大，反之亦然．人类活动是影响黄河下游泥沙灾害 的重要因素．

The Yellow River is famous in the world for the extremely serious sediment-related disasters in history. The bank-breaching frequency of the lower Yellow River is adopted as a proxy index to study such disasters. It is related to various indices describing the natural and human factors of the Yellow River basin. Consequently, some correlations have been established. Climate has profound influences on the bank-breaching frequency of the lower Yellow River. Before the Sui and Tang Dynasties(681-907, AD), natural vegetation in the middle Yellow River basin was not yet destroyed by human significantly. With the increase in humid index, growth of vegetation became better, then the bank-breaching frequency of lower Yellow River declined. After the 10th century, however, the relation between bank-breaching frequency and humid index became inverse, i. e. with the increase in humid index, bank-breaching frequency also increased. This is because, to a great degree, the natural vegetation had been destroyed since the 10th century. The bank-breaching frequency can be positively correlated to the frequencies of both great flood and drought disasters. The positive correlation between bank-breaching frequency and frequency of great drought disasters is because the Yellow River channel became shrunk during dry periods so that when large floods came, bank-breachings were more likely to occur. Based on some tree-ring data, the relation between bank-breaching frequency of lower Yellow River and temperature has been studied. The results indicate that, at 50-year scales, when temperature becomes lower, bank-breaching frequency increases, and vice versa.