陕北统万城地区历史自然景观及毛乌素沙漠迁移速率

Historical natural landscape of Tongwancheng area in northern Shaanxi Province and migration rate of Mau Us Desert

十六国时期夏国都城———统万城位于陕西省靖边县城北无定河北岸 ,今天的自然景观属于沙漠 ,仅存稀疏的次生灌丛和草本群落。但是 ,在约 16 0 0年以前 ,当地为温带干草原 ,在塬面或山丘上分布有侧柏林 ,沟谷、河岸边生长喜温湿的乔木 ,河流、湖泊、沼泽中水生植物繁盛 ,在丘间低洼处或盐碱土上分布有灌木和草本植物。当时该地区的年平均温度为 7 8℃～ 9 3℃ ,最热月平均温度 2 3 0℃～ 2 4 9℃ ,最冷月平均温度- 12℃～ - 5 6℃ ,年较差 2 8 5℃～ 38 2℃ ,年降雨量 4 0 3 4～ 5 5 0 0mm ,最大月降雨量 83 8～ 12 3 9mm ,最小月降雨量为 4 4～ 12 2mm。当时的年平均温度比现在高出 0 2℃～ 0 7℃ ,年降雨量也高出 6 0～ 10 0mm。如此的历史景观今天已经向南迁移 ,侧柏林或森林草原退缩至延安以南。在此近 16 0 0年的时间里 ,毛乌素沙漠分布范围不断扩大 ,其南部边缘推进了约 2 0 0km ,推测沙漠扩展的速率达到平均 12 5m/a。

Tongwancheng,the capital of the Great Xia Kingdom during the period of Five Hu and Sixteen Kingdoms in the Chinese history,was situated on the north bank of Wudinghe River in the north of Jingbian County,Shaanxi Province The recent Tongwancheng area has a desert landscape,with only sparse secondary shrub and grass community However,about 1600 years ago the Tongwancheng area was once a beautiful place of dry steppes with the landscape of sparse forest There was a temperate vegetation Forests of Platycladus orientalis were distributed on the hills and uplands Thermophilous trees grew along river banks and in gullies Abundant aquatic plants grew in rivers,lakes and swamps Salt loving shrubs and herbs covered the salinized soil At that time,the climate of the Tongwancheng area was as follows:the annual mean temperature was 7 8℃～9 3℃,the hottest monthly mean temperature was 23 0℃～24 9℃ and the coldest monthly mean temperature was -12 0℃～-5 6℃,the annual mean temperature difference was 28 5℃～38 2℃,the annual precipitation was 403 4～550 0 mm,the monthly maximum precipitation was 83 8～123 9 mm and the monthly minimum precipitation was 4 4～12 2 mm Compared with the present climate,the annual mean temperature and annual precipitation were respectively 0 2℃～0 7℃ and 60～100 mm higher It indicates that the climate in the Tongwancheng area about 1600 years ago was slightly warmer and wetter than the present time The similar vegetative landscape of dry steppes has moved southward The forests of Platycladus orientalis and forest steppe have moved to the southern part of Yan'an area It is estimated that the Mau Us Desert migrated southward at a mean rate of 125 meters per year during the past 1600 years