乌兰布和沙漠风沙入黄影响因子变化特征

乌兰布和沙漠是黄河上游内蒙古河段风沙的主要来源区，风沙入黄影响因子的变化会直接改变入黄风沙量，并进而对黄河水沙输移以及河床演变产生一定影响。依据野外调查和遥感影像，对河道边界条件、土地利用状况、沙漠所在区域风力条件和沙尘暴特征等风沙入黄影响因子进行了研究，揭示了其变化特征和趋势。结果表明：乌兰布和沙漠沿黄边界已发生很大变化，沿黄区域已修建一定规模的大堤，重新界定了河道范围，流动沙丘临河段长度较20世纪80年代大大减少，半固定沙丘多分布在距河道较远的地方，中间已被农田、村庄和开发地阻隔；沙漠所在区域年均风速及年最大风速总体上呈下降趋势，其中年均风速自20世纪50年代至今降低了1~1.3 m·s^-1，年最大风速较20世纪90年代初期降低6~10 m·s^-1；风力条件的变化导致了沙尘暴发生频率的降低，进而使得入黄风沙量减少，其影响周期与气候变化的周期有关。

Variation of Impact Factors on the Aeolian Sand blown into the Yellow River in the Ulanbuh Desert Area

Ulanbuh Desert is the main source of aeolian sand blown into the Upper Yellow River. Previous studies on the aeolian sand focused on the amount entering into the Yellow River and rarely involved variation of the influence factors that determine the amount variation of aeolian sand. Channel bank boundary, land use along the desert, and wind conditions and sandstorm frequency since 1950s have been analyzed with the long-term variation characteristics. Results showed that:The left levee with 33.086 km long has been built since 1990s, which redefined the left scope of the river. There are a 4.05-km-long movable dune adjacent to the river that has decreased greatly in comparison to that in 1980s. The semi-fixed dunes have a long distance to the river, where villages, farmlands, and land developed between the river and semi-fixed dunes. Meanwhile, the mean annual wind speed in the desert region has reduced by 1.0-1.3 m·s^-1 since 1950s, and the maximum annual wind speed has also reduced by 6.0-10.0 m s^-1 since early 1990s. Change of land use and the construction of the embankment somewhat restrain the amount of aeolian sand blown into the Yellow River. Variation of the meteorological conditions leads to the decrease of the frequency of sandstorms so as to reduce the aeolian sand amount accordingly. Moreover, the period of the meteorological conditions influencing aeolian sand is closely related to the cycle of climate change.