近一千年来贺兰山积雪和气候变化

通过对历史文献中关于贺兰山积雪变化记录的研究,以及其他反映贺兰山气候变化的环境信息的分析,确认贺兰山地区西夏、元明时期为冷凉气候,积雪特征反映的气候变化与中国西部气候变化相一致。通过贺兰山与天山、太白山、点苍山积雪变化的比较,发现其时间变化过程和演化规律具有一致性,进而对12世纪寒冷期永久积雪下限进行推测。根据对一千年来贺兰山年日最低气温≤0℃日数的计算,认为12世纪寒冷期年平均气温较现代约低1.5²℃,推算当时贺兰山永久积雪下限为海拔3400³500m;以17世纪中叶为代表的小冰期年平均气温较现代约低1¹.5℃,推算当时贺兰山永久积雪下限为海拔3500³600m。

Investigation on changes of snow cover and climate in Helanshan mountains for the past approximate millennium

For the past approximate millennium, the general changing trend in climate is warmer due to the snow fall in summer and winter and snow cover for the whole year in the Western Xia regime,the snow cover for the whole year in the Ming Dynasty,and snow cover without snow fall in the summer of the early Qing Dynasty according to the historic snow cover record of the Helanshan mountains.Also it is confirmed that the period from the Western Xia regime to the Yuan and Ming dynasties witnessed cold climate,and the characteristics of the snow cover reflected climate change agreed well with the characteristics of the climate change in western China.It is found that the time change process and the change regularity are of agreement,and the inference for the minimum limit of permanent snow cover of the cold stage in the 12^th century was given by comparing historic snow cover changes of Halanshan,Tianshan,Taibaishan and Diancangshan mountains. Helanshan recorded the climate change in a specific stage.In the warm stage of the Middle ages,Helanshan presented the characteristic cold and cool climate of the western China,and gave an evidence of the existence of the cold stage in the 12^th century by the snow cover and the other environmental record.It showed the characteristic of both cold and wet,and the decline of snow line.The Little Ice Age was also reflected in the record of the Helanshan mountains,i.e.,it was cold and dry with decreasing in snow line. According to the relationship between the number of the annual lowest temperature（≤0℃） days and the annual mean temperature of the Helanshan Observatory and taking into the consideration of the change in temperature in the specific stage,the inferences that annual mean temperature of the cold stage in Helenshan in the 12^th century was predicted to be 1.5²℃ lower than the present, and the lower limit of the permanent snow cover was estimated to be 3400 to 3500m;the annual mean temperature of the Little Ice Age in the 17^th century was 1¹.5℃ lower than that of the present and the lower limit of the permanent snow cover decreased to 3400 to 3500m were also given.