3500aBP我国北方农牧交错带降水突变的幅度与速率

考古信息与历史文献记载一样是环境演变研究中独具特色的信息源。文章以考古信息为依据对中国北方农牧交错带地区 35 0 0aBP前后降水突变的幅度与速率进行了推断。中国北方农牧交错带分布在年降水量 2 5 0～ 40 0mm的地区 ,降水变化对该地带的影响十分显著。在位于北方农牧交错带内的内蒙古中南部及陕北、晋西北地区 ,大量的考古遗存详细记录了 35 0 0aBP前后该地区内土地利用性质的时空变化过程 ,可以用来定量地估算 35 0 0aBP降水突变的幅度和速率。 42 0 0～34 0 0aBP期间 ,在内蒙古中南部及陕北、晋西北地区先后发育了朱开沟文化和李家崖文化。文化的演变过程可分为两个阶段 :从朱开沟一期到朱开沟二期为第一阶段 (cal.40 0 0～ 380 0aBP) ,在朱开沟文化区发生了从农业文化转变为农牧交错文化、进而变为畜牧业文化的过程 ,相当于从农业区的北界变为农牧交错区的北界 ;从朱开沟文化二期结束到李家崖文化为第二阶段 (cal.380 0～ 34 0 0aBP) ,期间农牧交错带的北界显著地向东南退缩。上述考古学文化的变化可以看作是人类对 35 0 0aBP前后降水突变的响应。 40 0 0aBP前后是从农业文化向半农半牧文化转变的临界点 ,其降水量大致与现代农牧交错带南界的降水量相当 ,为 35 0～ 40 0mm ;380 0aBP前后是从半

RANGE AND RATE OF ABRUPT CHANGE OF PRECIPITATION AROUND 3 500 a BP IN THE NORTH CHINA FARMING-GRAZING TRANSITIONAL ZONE

Proxy data from archeological records are as important as that from historical documents for reconstruction of past environment changes. In this paper, the archeological records are used to infer the range and rate of abrupt change of precipitation around 3500aBP in the north China farming-grazing transitional zone. The contemporary north China farming-grazing transitional zone locates in the region that the annual precipitation is between 250 mm to 400 mm. The region is sensitive to the precipitation change. In the region of Mid-south Inner Mongolia, Northern Shaanxi and Northwestern Shanxi, part of the modern north China farming-grazing transitional zone, there are abundant archeological records indicating the changes of the land use, which can be used as the evidence for inferring the abrupt change of precipitation around 3500aBP in the region.During cal. 4 200～3 400 a BP, the archeological cultures of Zhukaigou Culture and Lijiaya Culture were developed in the region of Mid-south Inner Mongolia, Northern Shaanxi and Northwestern Shanxi. The changes of the cultures can be divided into two stages. During the first stage, from the end of Phase Ⅰ (cal.4 200～4 000 a BP) to the end of Phase Ⅱ(cal.4 000～3 800 a BP) of the Zhukaigou Culture, the culture was changed from the primitive agriculture to the farming-grazing culture, then to the pasture culture, which is equivalent to such a change of the boundary of the farming-grazing transitional zone that the southern boundary became the northern boundary. During the second stage, from the end of Phase II of Zhukaigou Culture(cal.4 000～3 800 a BP) to the Lijiaya Culture, the northern boundary of the north China farming-grazing zone shifted southeastward sensitively.The change of the patterns of land use associated with the changes of the archeological cultures mentioned above could be regarded as the response of human being to the abrupt change of precipitation around 3500aBP. 4000aBP was the turning point of the land use from agriculture to half farming and half grazing, when the annual precipitation was about 350～400mm, the annual precipitation at the southern boundary of modern farming-grazing transitional zone. 3800aBP was the turning point of the land use from half farming and half grazing to pasture, when the annual precipitation was about 250～300mm, the annual precipitation at the northern boundary of modern farming-grazing transitional zone. So from 4000aBP to 3800aBP, the annual precipitation reduced 100mm within 200 years. From 3800aBP to 3400aBP, the northern boundary of farming-grazing transitional zone shifted southeastward from the position of 400mm isohyet to 450～500mm isohyet of modern precipitation. It is equal to the annual precipitation reduction of 50～100mm in 400 years. In sum, the annual precipitation had reduced 150～200mm in the 600 years from cal.4000aBP to cal.3400aBP. The average decline rate was 25～33mm/100a.