过去2000年黄河中下游气候与土地覆被变化的若干特征

Changes of climate and land cover in the middle and lower reaches of the Yellow River over the past 2000 years

根据近40年在黄河中下游地区气候、灾害、植被与土地利用变化历史等方面的研究成果,综合分析了过去2000年黄河中下游地区温度、干湿、极端旱涝等的变化特征,以及历史农耕发展对土地覆被的改变和垦殖率变化的总体趋势;并从长期变化视角简要讨论了这些变化与黄河下游地区泥沙淤积、决口改道的宏观关系。主要结论有:过去2000年黄河中下游地区温度与干湿呈显著多尺度周期波动,且中游和下游地区的干湿变化并不完全同步;极端旱涝发生频率存在阶段性差异。至公元初前后,黄河中下游地区就已被开发为一个垦殖范围与今相近的农业区,其自然植被分布极为有限,且其后的农耕垦殖强度虽有大幅波动,但总体呈增加趋势。上述因素变化相互交织影响了黄河中、下游水沙输送平衡、河道淤积和河床稳定,是引发历史上黄河下游多次重现"筑堤—淤积—悬河—决口改道"循环过程的重要因素。这些认识可为进一步科学理解黄河中下游地区的环境变化规律及其与下游地区河流安澜的关系提供历史背景依据。

Based on the research on the changes of climate,disasters,vegetation,and land use in the past 40 years,this study made a comprehensive assessment of the characteristics of changes of temperature,dry/wet conditions,and extreme droughts and floods,and the general trend of land cover caused by the agricultural land use,in the middle and lower reaches of the Yellow River over the past two millennia.We also discussed the general relationships between the above changes and the sedimentation,breaches,and avulsions in the lower Yellow River from a historical perspective.The main conclusions are as follows.(1)During the past two millennia,multi-scale periodic fluctuations of temperature and dry/wet conditions were significant in the middle and lower reaches of the Yellow River,but the dry/wet changes in the middle and the lower reaches were not completely synchronized.Frequencies of extreme droughts and floods varied in different time periods.(2)As early as in the late Western Han Dynasty,the middle and lower reaches of the Yellow River had already been developed into an agricultural area with a spatial range similar to today’s,where,especially on relative flat terrains,only limited natural vegetation remained.Since then,the intensity of reclamation showed an increasing trend in general,although it fluctuated greatly over time.(3)The changes of climate and land cover had influenced the water-sediment balance,channel sedimentation,and riverbed stability in the middle and lower reaches of the Yellow River,and driven,as an important trigger,the repeated diking-sedimentation-suspended river-burst and avulsion cycle in the lower Yellow River during the historical period.These understandings can provide historical backgrounds for further revealing the characteristics of environmental change in the middle and lower reaches of the Yellow River and their impacts on the security of the lower Yellow River region.